BIOLOGY, STOCK ASSESSMENT AND FISHERY

MANAGEMENT OF THE SANTER SEABREAM CHEIMERIUS

NUFAR (VAL. 1830) FROM THE ARABIAN SEA OFF OMAN

Dissertation Submitted By

Abdulaziz Said Mohamed Al-Marzuqi

In partial fulfilment of the requirements for the degree of

Doctor of Natural Sciences (Dr. rer. nat.)

Leibniz Center for Tropical Marine Ecology

Faculty of Biology / Chemistry

University of Bremen

February 2011

I

Zusammenfassung

Im Mittelpunkt der Dissertation steht die Biologie und die fischereibezogene

Einschätzung von Santer seabream, Cheimerius nufar (Valenciennes, 1830), entlang der

Küste des Arabischen Meeres des Sultanates Oman in den Jahren 2005-2008. Zusätzlich

wurden die saisonbedingte Verteilung bestimmter Umweltparameter im Arabischen Meer

und ihr Einfluss auf den Bestand von C. nufar untersucht. Diese Untersuchungen basieren

auf Einschätzungen der Grundfischerei durch das Forschungsschiff AL Mustaqila 1 in

dem Zeitraum September 2007 – September 2008. Vier Untersuchungsgebiete wurden

erfasst.

Wichtige Ergebnisse der Studie bezüglich C. nufar werden weiter unten

zusammengefasst.

� Die Oberflächentemperaturen lagen zwischen 25°C und 28°C in der Herbst-

Zwischenmonsunperiode (Sep – Dez), fielen dann nach der NE-Monsunperiode

(Feb) auf 22°C – 24°C und stiegen dann erneut in der Frühjahrs-

Zwischenmonsunperiode (Apr. – Jun.) auf 25°C – 28°C an. Die

Oberflächentemperatur war generell gering (18°C – 24°C) unmittelbar nach dem

SW-Monsun. In Küstennähe (20-50 m Schicht) war die Bodentemperatur mit 25°C

am höchsten während der Herbst-Zwischenmonsunperiode (Sep-Okt) im Jahre

2007 und am geringsten (17°C) unmittelbar nach dem SW-Monsun im Jahre 2008.

� Der Seeoberflächensalzgehalt schwankte wenig während der Untersuchungen und

lag im Bereich zwischen 36 und 37 ppt. Einen geringeren Salzgehalt (34ppt)

wiesen im Jahre 2008 lediglich die Gewässer südlich der Insel Masirah unmittelbar

nach der SW-Monsunperiode auf. Kleine Taschen mit einem höheren Salzgehalt

wurden im Gebiet 3 des Schelfs beobachtet. Der Bodensalzgehalt zeigte ein Bild

ähnlich dem Oberflächensalzgehalt.

� Der Gehalt an O2 im Oberflächenwasser war in allen Gebieten während der

Untersuchungen hoch (4-6 ml l-1). Die Sauerstoffminimumzonen (OMZs) waren

die pelagischen Zonen mit geringem Sauerstoffgehalt die sich nach unten

erstreckten direkt von der Mischschicht bis zu einer Tiefe von mehr als 1000 m in

II

einigen Gebieten. Der Bodensauerstoffgehalt war gering in den meisten der

Untersuchungsgebiete während der Frühjahrs-Zwischenmonsunperiode (Apr-Jun).

� Es gab Unterschiede im Vorkommen von C. nufar während der Untersuchungen

die in der Periode nach dem Südwestmonsun 2007 und 2008 durchgeführt wurden.

Der Fisch trat auf bei Temperaturen zwischen 20°C und 24°C während des NE-

Monsuns und bei Temperaturen zwischen 26°C-28°C während des Frühjahrs-

Zwischenmonsuns. Während des Post-Südwest-Monsuns wurde der Fisch bei

Temperaturen zwischen 17°C und 21°C angetroffen. Der Fisch C. nufar scheint

an ein geringes Sauerstoffniveau während der verschiedenen

Untersuchungsperioden angepasst zu sein.

� Der geschätzte Fang an C. nufar während der Jahre 2005-2006 bzw. 2006-2007

betrug 2075t bzw. 2018t.

� Die Größe der kommerziellen Anlandungen an C. nufar erstreckt sich von 16 cm

TL bis 64 cm TL.

� Etwa 67.5% des Fanges bestand aus Fisch mit einer Länge unter 32 cm TL.

� Da die Längen-Gewichts-Beziehung von männlichen und weiblichen Exemplaren

sich nicht signifikant unterscheidet, kann die übliche Gleichung W=0.019L2.897 für

diese Fischart benutzt werden.

� Diese Fischart ist ein Fischfresser, der sich gelegentlich von cephalopoden,

crustacaens und polychaetes ernährt.

� Leere Mägen waren üblich in all den Monaten und Reifestadien des Fisches.

III

� Es wurden Inkonsistenzen bezüglich der Intensität der Nahrungsaufnahme des

Fisches in den verschiedenen Stadien der Reife bei beiden Geschlechtern

festgestellt.

� Die mittlere Erstlaichlänge der weiblichen Fische (31.9 cm TL) war geringer als

die der männlichen (33.7 cm TL).

� Die Laichreife tritt bei beiden Geschlechtern zu Beginn des dritten Jahres ein.

� Die Population von C. nufar laicht während der Monate Mai – Oktober. Einzelne

Fische scheinen zweimal im Jahr zu laichen.

� Die Fertilität erstreckt sich von 11406 – 473277 Eier.

� Es wurde keine Dominanz einer der Geschlechter in der Population beobachtet.

Ein Test des monatlichen und jährlichen Geschlechterverhältnisses mittels Chi-

Square-Test ergab keinen signifikanten Unterschied.

� Folgende VBG-Parameter wurden für C. nufar ermittelt: basierend auf

Längenfrequenzanalysen L∞ = 69,9 cm, K = 0.29 y-1 und t0 = -0,32 y und

basierend auf Otholithenanalysen für männliche Fische L∞ =66,47 cm, K = 0,1937

y-1 und t0 = -0,36055 y und für weibliche Fische L∞ = 69,77 cm K = 0,182 y-1

und t0 = -0,24886 y. Das maximale Alter basierend auf Längenfrequenzen wurde

mit etwa 11 Jahren geschätzt; der Otholith gibt jedoch eine Lebensdauer von etwa

13 Jahren an. Der Wachtumsindex (�) von C. nufar erreichte in diesen

Untersuchungen basierend auf Längendaten einen Wert von 3,14 und basierend

auf Othlithenanalysen einen Wert von 2,95. Hieraus folgt, dass diese Fischart

vergleichsweise in den Gewässern Omans schnell wächst.

� Die ermittelte Fanglänge (Lc) betrug 31,4 cm. 67,4% der kommerziell

angelandeten Fische wies eine Länge <34 cm auf.

IV

� Die ermittelten Koeffizienten totale Sterblichkeit (Z), natürliche Sterblichkeit (M)

und Fischereisterblichkeit (F) wiesen die Werte 1,3, 0,62 und 0,68 auf.

� Das ermittelte M/K – Verhältnis weist den Wert 2,13 auf.

� Die Ausbeutungsrate (E) für die Untersuchungsperiode ist gleich 0,52.

� Der geschätzte MSY für den Bestand an C. nufar betrug bei Anwendung der

Formel von Cadima 1953 t und bei Anwendung des Thompson und Bell Models

1946 t.

� Das durchschnittliche beständige Aufkommen wurde auf 3010 t geschätzt.

� Der mittlere totale Bestand (Y/U) wird auf 5387 t geschätzt.

� Die vorhergesagte totale Biomasse von 16052 t verringert sich auf 12713 t bei

einem Wert F=0,1, auf 6167 t bei einem Wert von F=0,5 und auf 5235 t bei einem

Wert von F=0,6. Bei einem Wert von F=2,0 betragen der Ertrag und die Biomasse

18 t bzw. 57 t.

� Bei dem gegenwärtigen Wert von F (=0,68) erreichen die Beziehungen Yw/R,

TB/R, SSB/R und FB/R die Werte 111 g, 260 g, 191 g und 163 g.

� Die vorliege Studie zeigt das der Bestand an C. nufar an der Küste Omans des

Arabischen Meeres geringfügig überausgebeutet ist. Die mittlere Größe des zu

fangenden Fisches sollte auf 36 cm TL begrenzt werden. Weiterhin ist es zur

Erreichung eines nachhaltigen dauerhaften Ertrages zu empfehlen das derzeitige

Aufwandsniveau um 17% zu senken.

V

Summary

This thesis focuses on the biology and fishery assessment of the santer seabream,

Cheimerius nufar (Valenciennes, 1830) along the Arabian Sea coast of the Sultanate of

Oman during 2005–2008. In addition the seasonal distribution of certain environmental

parameters in the Arabian Sea and their influence on the stock of C. nufar were studied

based on the demersal fishery resources survey conducted by the R.V. Al Mustaqila 1

during Sept 2007 – Sept 2008 covering four survey areas.

The Important findings of the study on C. nufar are summarized below.

� Sea surface temperature tended to be warmest that ranged between 25 ºC and 28 ºC

during the autumn intermonsoon period (Sept–Dec), cooled after the NE

monsoon period (Feb) to 22 ºC – 24 ºC, warmed again to 25 ºC – 28 ºC during

the spring intermonsoon period (Apr–Jun), and was generally very cool (18 ºC -

24 ºC) immediately after the SW monsoon. Nearshore (20–50 m strata) bottom

temperatures w ere highest 25 ºC during the autumn intermonsoon period (Sept-

Oct) in 2007 and were coolest (17 ºC) immediately after the SW monsoon in

2008.

� Sea surface salinity varied little throughout the surveys that ranged between 36

and 37 ppt except for immediately after the SW monsoon period in 2008 when

waters south of Masirah Island were less saline (34 ppt), although small pockets

of higher saline waters were seen in area 3 on the shelf. Bottom salinity showed

a pattern similar to surface salinity.

� Dissolved O2 in the surface water was high (4–6 ml l-1) in all areas dur ing

al l thesurveys. The OMZs were the midwater zones of low oxygen that extend

from just below the mixed layer to more than 1000 m in some areas. Bottom

oxygen was low in most of the survey areas during the spring intermonsoon

period (April–June).

VI

� There was difference in the distribution pattern of C. nufar between the surveys

done in the post southwest monsoon periods of 2007 and 2008. The fish

occurred at temperatures between 20ºC and 24ºC during NE

monsoon and spring inter-monsoon and at 26ºC-28ºC during

autumn inter-monsoon. During post -southwest monsoon of 2008

the fish was found at temperatures between 17ºC and 21ºC. The

fish C. nufar appeared to adapt to low oxygen level during

different periods of survey.

� The catches of C. nufar were estimated at 2,075 t and 2018 t during 2005-2006

and 2006-2007 respectively.

� The size of C. nufar in the commercial landings ranged from 16 cm TL to 64 cm

TL.

� About 67.5% of the catch composed of fish measuring less than 32 cm TL.

� As the length-weight relationships of males and females did not differ significantly,

the common equation W = 0.019L2.897 can be used for the species.

� The species is a piscivore feeding occasionally on cephalopods, crustaceans and

polychaetes.

� Empty stomachs were common in all the months and maturity stages of fish.

� There was inconsistency in feeding intensity of fish in different stages of maturity

in both the sexes

� The average length at first maturity in female (31.9 cm TL) was lower than in

male (33.7 cm TL).

� The maturity in both males and females appeared to attain at the beginning of

third year.

� The population of C. nufar spawned during May – October and individual fish

appeared to spawn twice a year.

VII

� Fecundity of ranged from 11,406 - 473,277 of eggs.

� There was no dominance of either sex in the population and the monthly and

annual sex-ratios tested by chi-square test did not differ significantly.

� The calculated VBG parameters of C. nufar based on length frequency analysis

were: L∞ = 69.9 cm, K = 0.29 y-1 and t0 = -0.32 y. and based on otolith study

were : for the male, L∞ = 66.47 cm, K = 0.1939 y-1 and t0 = -0.36055 y and for

female, L∞ = 69.77 cm, K = 0.182 y-1 and t0 = -0.24886 y. The estimated

maximum age based on length frequency would be around 11 years; however,

otolith indicated the longevity of about 13 years. The growth performance index

(Ø’) of C. nufar in the present study was estimated at 3.14 based on length data

and 2.95 based on otolith analyses suggested the species is comparatively growing

fast in the Omani waters.

� The calculated length at capture (Lc) was 31.4 cm and about 67.4% of the fish in

the commercial catches measured < 34 cm.

� The estimated total mortality (Z), natural mortality (M) and fishing mortality (F)

coefficients were 1.3, 0.62 and 0.68 respectively.

� The M/K ratio estimated for the species was 2.13.

� The exploitation rate (E) for the period of study stood at 0.52.

� The estimated MSY for the stock of C. nufar by Cadima’s formula was 1,953 t

and by Thompson and Bell model was 1,946 t.

� The average standing stock was estimated as 3,010 t.

� The estimated average total stock (Y/U) stood at 5,387 t.

� The predicted total biomass of 16,052 t decreased to 12,713 t at F=0.1, to 6,167 t

at F= 0.5 and to 5,235 t at F= 0.6. At F= 2.0, the yield and biomass stood at 18 t

and 57 t respectively

VIII

� At the current F (= 0.68), the values of Yw/R, TB/R, SSB/R and FB/R were found

to be 111 g, 260 g, 191 g and 163 g respectively.

� The present study indicates the stock of C. nufar in the Arabian Sea off Oman is

marginally overexploited. The average size of the fish to be caught may be

restricted to 36 cm TL. Further, a reduction of 17% of effort from the present

level of effort is recommended for obtaining sustainable yield.

IX

Acknowledgements

First of all my thanks to the God, who created me, helps me and has given me the health

and ability to reach this stage. I would like to express my thorough respect and

appreciation to my supervisor, Prof. Dr. Ulrich Saint-Paul, who freely discussed my ideas

for this study, for his helpful guidance, advice and valuable comments. I extend my

thanks to my co-supervisor Dr.Werner Ekau for his incessant support throughout my

study period. Special thanks go to my local supervisor Prof. Dr. Nachiappan Jayabalan

for his valuable advice and comments. I appreciated his quality and friendly supervision.

I would like to thanks my Government, Sultanate of Oman, represented by Ministry of

Fisheries Wealth for offering me this scholarship.

I would like to thanks my colleagues in the Marine Science and Fisheries centre for their

support and the invaluable assistance they provide in getting the needed information for

this study.

Finally, I would like to record my sincere appreciation of the love, sacrifices and

unlimited help and support of my family who encouraged me to study and overcome all

obstacles and who always pray and worship God for my success.

X

Table of Contents

Summary………………………………………………………………………………….I

Acknowledgement……………………………………………………………………....IX

Table of Contents………………………………………………………………………..X

List of Figures………………………………………………………………………....XII

List of Tables…………………………………………………………………………XVI

1. INTRODUCTION…………………………………………………………………....1

1.1. Literature review…………………………………………………………………..1

1.2. The Study Area……………………………………………………………………4

1.3. Aims of the study………………………………………………………………….7

2. MATERIALS AND METHODS..........................................................................…...8

2.1. Sampling procedure of the Arabian Sea Survey ………………………………….8

2.1.1. Resource Assessment Survey of the Arabian Sea Coast of Oman…………..8

2.1.2. Survey area, design, stratification and station allocation…………………….8

2.1.3. Survey procedure and data collection………………………………………10

2.2. Collection and analysis of C. nufar samples from landing sites………………...12

2.2.1. Age and growth estimation…………………………………………………12

2.2.2. Maturation and spawning…………………………………………………...15

2.2.3. Food composition and feeding intensity……………………………………18

2.2.4. Population dynamics and stock assessment………………………………...19

3. RESULTS……………………………………………………………………………22

3.1. Seasonal distribution of physico-chemical characteristics of the water of the

Arabian Sea………………………………………………………………………22

3.2. Study of C. nufar………………………………………………………………...37

3.2.1 Age and growth estimation……………………………………………………..39

3.2.2. Maturation and spawning………………………………………………………54

3.2.3. Food composition and feeding intensity……………………………………….72

3.2.4. Population dynamics and stock assessment……………………………………79

XI

3.3. Distribution of C.nufar in relation to oceanography parameters…………………82

4. DISCUSSION……….………………………………………………………………..87

5. REFERENCES……………………………………………………………………….97

XII

List of Figures

Fig. 1. Sultanate of Oman geographical location……………………………………5

Fig. 2. Survey area and stations in the Arabian Sea…………………………………10

Fig. 3. Post- SW monsoon 2007: Sea surface temperature…………………………..22

Fig. 4. Autumn inter- monsoon 2007: Sea surface temperature……………………..23

Fig. 5. NE monsoon 2008: Sea surface temperature…………………………………23

Fig. 6. Spring Inter- monsoon 2008: Sea surface temperature……………………….24

Fig. 7. Post- SW monsoon 2008: Sea surface temperature…………………………..24

Fig. 8. Post- SW monsoon 2007: Bottom temperature………………………………25

Fig. 9. Autumn Inter-monsoon 2007: Bottom temperature………………………….26

Fig. 10. NE monsoon 2008: Bottom temperature……………………………………26

Fig. 11. Spring Inter-monsoon 2008: Bottom temperature…………………………..27

Fig. 12. Post- SW monsoon 2008: Bottom temperature……………………………..27

Fig. 13. Post- SW monsoon 2007: Surface salinity………………………………….28

Fig. 14. Autumn monsoon 2007: Surface salinity…………………………………...29

Fig. 15. NE monsoon 2008: Surface salinity………………………………………...29

Fig. 16. Spring Inter-monsoon 2008: Surface salinity…………………………….…30

Fig. 17. Post- SW monsoon 2008: Surface salinity…………………………………30

Fig. 18. Post- SW monsoon 2007: Bottom salinity………………………………….31

Fig. 19. Autumn monsoon 2007: Bottom salinity…………………………………...32

Fig. 20. NE monsoon 2008: Bottom salinity………………………………………...32

Fig. 21. Spring Inter-monsoon 2008: Bottom salinity……………………………….33

XIII

Fig. 22. Post- SW monsoon 2008: Bottom salinity………………………………..….33

Fig. 23. Post- SW monsoon 2007: Bottom dissolved oxygen………………..……….34

Fig. 24. NE monsoon 2008: Bottom dissolved oxygen…………………………....….35

Fig. 25. Spring inter-monsoon 2008: Bottom dissolved oxygen……………………...36

Fig. 26. Post- SW monsoon 2008: Bottom dissolved oxygen………………………...36

Fig. 27. C. nufar distribution from all trawl survey stations……………………….…38

Fig. 28. Biomass of C. nufar in different depth zones in the Arabian Sea survey ………...…38

Fig. 29. Length frequency distribution of C. nufar in the commercial catches during

2005-06………………………………………………………………………39

Fig. 30. Length frequency distribution of C. nufar in the commercial catches during

2006-2007……………………………………………………………………40

Fig. 31. Pooled length frequency distribution of C. nufar in the commercial catches

during 2005-2007............................................................................................ .40

Fig. 32. Total length-fork length relationship in C. nufar …………………………....41

Fig. 33. Length-weight relationship in C. nufar……………………………………....42

Fig. 34. VBGF curve of C. nufar by SLCA technique………………………………..42

Fig. 35. VBGF curve of C. nufar by PROJMAT technique………………………..…43

Fig. 36. VBGF curve of C. nufar by ELEFAN 1 technique…………………………..43

Fig. 37. Age distribution of C. nufar in the commercial catches during 2005-2007….45

Fig. 38. Growth curves derived from length frequency analyses in C. nufar…………46

Fig. 39. Length at first capture of C. nufar…………………………………………...46

Fig. 40. Photomicrograph of a transverse section through the sagittal otolith………..47

XIV

Fig. 41. Monthly percentage of otoliths with hyaline and opaque edge………………48

Fig. 42. VBGF curves for C. nufar, Female (n =159) and Male (n =99)……………..49

Fig. 43 A. Development of ova to maturity stage I in C. nufar……………………….55

Fig. 43 B. Development of ova to maturity stage II in C. nufar………………………55

Fig. 43 C. Development of ova to maturity stage III in C. nufar……………………..56

Fig. 43 D. Development of ova to maturity stage IV in C. nufar……………………..56

Fig. 43 F. Development of ova to maturity stage V in C. nufar………………………56

Fig. 44. Distribution of different maturity stages of gonads of C. nufar during2005-06………………………………………………………………………………..58

Fig. 45. Distribution of different stages of gonads of C. nufar during 2006-07………59

Fig. 46 - A. Fish with running ripe maturity stage during post SW monsoon 2007…..60

Fig. 46 - B. Fish with running ripe maturity stage during post SW monsoon 2008…..60

Fig. 47. Monthly gonado-somatic indices in C. nufar 2005 – 2007…………………..61

Fig. 48. Monthly hepato-somatic indices in C. nufar 2005 -2007………………….....62

Fig. 49. Monthly Kn in C. nufar 2005-2007…………………………………………..63

Fig. 50.Juveniles distribution -Post SW monsoon 2007……………………………....63

Fig. 51 Juveniles distribution: Autumn monsoon 2007……………………………….64

Fig. 52 Juveniles distribution –NE monsoon 2008…………………………………....64

Fig. 53 Juveniles distribution Spring Inter-monsoon 2008……………………………65

Fig. 54 Juveniles distribution -Post SW monsoon 2008……………………………....65

Fig. 55 Length at first maturity in C. nufar…………………………………………...66

Fig. 56 A. Fecundity in relation to total length (cm)………………………………….67

Fig. 56 B. Fecundity in relation to body weight(g)…………………………………...68

XV

Fig. 56 C. Fecundity in relation to ovary weight(g) of C. nufar……………………..68

Fig. 57. Sex ratio of C. nufar during the period April 2005 - March 2007……….......69

Fig. 58. General food composition of C. nufar during 2005-06………………………72

Fig. 59. General food composition of C. nufar during 2006-07………………………73

Fig. 60. Monthly percentage of composition of food items of C. nufar during2005-06 …………………………………………………………………....................74

Fig. 61. Monthly composition of food items of C. nufar during 2006-07…………….74

Fig. 62. Food items found in the gut of various size groups of C. nufar during2005-2007 (pooled)………………………………………………………....75

Fig. 63. Feeding intensity in C. nufar relation to months……………………………..76

Fig. 64. Feeding intensity in different maturity stages of C. nufar……………………77

Fig. 65. Feeding intensity in different size groups of C. nufar………………………..78

Fig. 66. Predicted yield for C. nufar for different F…………………………………..80

Fig. 67. Equilibrium yield-per-recruit and biomasses-per-recruit in C. nufar

against F………………………………………………………………….......81

Fig.68. Catch of C. nufar at different t ime of monsoon……………….82

Fig. 69 Distribution of C. nufar: Post SW monsoon 2007…………………………....83

Fig. 70 Distribution of C. nufar : Autumn monsoon 2007……………………………83

Fig. 71 Distribution of C. nufar: NE monsoon 2008………………………………….84

Fig. 72 Distribution of C. nufar: Spring Inter-monsoon 2008………………………...84

Fig. 73 Distribution of C. nufar: Post SW monsoon 2008…………………………...85

Fig.74 Catch rate of C. nufar by stratum during monsoon periods…………………...86

Fig.75. Occurrence of C. nufar at different level of bottom dissolved oxygen……......86

XVI

List of Tables

Table 1. Details of survey period, demersal fish survey and CTD stations …………..9

Table 2 Estimated biomass (t) and coefficients of variation for C. nufar……………....37

Table 3. Length – weight relationship parameters ……………………………………..41

Table 4. VBGF parameters of C. nufar estimated by different methods ………………44

Table 5. Growth parameters of male and female C. nufar using otolith reading……….49

Table 6 A. Age - length key for Male of C. nufar - sectioned otolith. …………………50

Table 6 B. Age - length key for female of C. nufar - with sectioned otolith. ………….51

Table 6 C. Age structure of C. nufar population in the Arabian Sea…………………...52

Table 6 D. Age structure of C. nufar population in the Arabian Sea…………………...53

Table 7A Sex-ratio in C. nufar during 2005-06………….………………………………70

Table 7B Sex-ratio in C. nufar during 2006 -07…………………………………………71

Table 8. Comparison of growth parameters of C. nufar from different studies………....90

1

1. Introduction

This thesis focuses on the fishery assessment of the santer seabream, Cheimerius

nufar along the Arabian Sea coast of the Sultanate of Oman during 2005–2008

taking into consideration of the influence of the environmental parameters. T h e

s tu d y w a s co nd u c t ed i n t wo p ha s es . While the phase-1 study was related

to the biology and stock assessment of C. nufar based on samples collected from the

commercial fish catches, phase-2 investigation was concerned with the distribution

of certain environmental parameters in the Arabian Sea and their influence on the

distribution of C. nufar based on the fishery resource survey conducted by the R.V.

Al Mustaqila 1. The work is situated in the context of an ongoing requirement for

the fisheries sector o f t h e c o u n t r y to manage the resource sustainably.

1.1 Literature review

The fisheries sector has always been important to Oman as a significant source of

a n i m a l p r o t e i n and employment. Prior to the discovery of oil and i t s

subsequent exploitation in the late 1960s, the fishing industry supported about

80% of the population, and even today, around 50% of Omanis rely upon fishing

as the source of income retaining its prominence within the limits of renewable

economic resources (MoI, 2 0 0 8 ).

Though, there is general increase in the total annual catch of fish in recent years, the

landings of quality fish have declined due to overexploitation (MAF, 2006). As in

most developing countries, Oman’s coastal fisheries are supported by multispecies,

more than 150 species of fishes and crustaceans (Al-Abdessalaam, 1995) and

harvested by multigear. The number of fishermen and the gears employed increase

from year to year and at present about 34,757 fishermen are engaged in fishing using

13,862 boats (GOSO, 2009). As the consequence, there is concomitant reduction in

the prosperity of coastal fisherfolk who depend upon fishing for their livelihood. The

reason for carrying out this study was due to the serious concerns repeatedly

raised o n the sustainability of demersal stocks and the welfare of the traditional

fishers despite long coastline and frequent reports of large number of foreign

vessels trawling in the closed areas of the Omani waters.

2

Prior to 1990s, a decline in total catch and reduction in the a v e r a g e size of

the individuals caught were recorded from the Omani waters; however, no specific

reason for the decline could be attributed (Siddeek, 1999). Besides, there has

been a shift from pelagic to demersal fishing in Oman as some of the higher value

pelagic species like the kingfish Scomberomorus commerson were depleted (Siddeek

et al., 1998).

The sparid C. nufar is locally known as ‘kofwar’ or ‘frenka’ inhabits inshore waters

up to the depth of 60-100 m and forms an important component of the demersal

fishery of Oman targeted by both the traditional fishers using handlines and gillnets

and by industrial trawlers (Abdessalaam, 1995). Due to its high demand in the

market, increased fishing pressure has lead to overexploitation of the stock

(Abdessalaam, 1995). The estimated biomass and potential yield from the stocks of

all the sparids of Oman were reported to be around 40,000 t and 6,000 t respectively

(Abdessalaam, 1995). The estimated catches of C. nufar from the Arabian Sea coast

of Oman for the years 2005-06 and 2006-07 were 2,075 t and 2,018 t respectively

(GOSO, 2005; 2006; 2007). While the contribution of all sparids to the annual total

catch of Oman was about 4.2% with a value of about US$ 11.95 million during

2007; the catches of C. nufar represented about 45% of the sparid catches from

Arabian Sea with an estimated value of about US$ 5.38 million (GOSO, 2007).

Fishes of the family Sparidae are represented by nineteen species in the Omani

waters (Fouda et al., 1997) and many of them contribute to the traditional and

industrial fisheries of the country (GOSO, 2007). The santer seabream, C. nufar is a

moderate sized fish and is distributed in the western Indian Ocean including the Red

Sea, coasts of Oman, Arabian Gulf, eastern African coast, Madagascar and the

Mascarene Islands (Bauchot and Smith, 1984; Smith and Smith, 1986; Randall,

1995; Connell et al., 1999). Individuals of C. nufar may attain a total length of 75 cm

and weigh about 6 kg; however, most of the fish caught are in the weight range of 1

to 3kg (Connell et al., 1999). Detailed studies on the biology and population

structure on C. nufar are available from the Gulf of Aden (Druzhinin, 1975; Edwards

et al., 1985.), South African coasts (Coetzee and Baird, 1981; Coetzee, 1983,

3

Garratt, 1985, 1985a, 1991; Smale, 1986; Buxton and Garratt, 1990) and

Mozambique (Timochin, 1992).

Though, C. nufar is a priority species and intensively fished in Oman, except the

report on its spawning and reproductive pattern (McIlwain et al., 2006), no other

study on fishery biological characteristics of the species is available. Presently, an

attempt has been made to study the biological and population parameters of C. nufar

from the Arabian Sea harvested by artisanal gears for two years from April 2005 to

March 2007. Subsequently, the distribution pattern of the environmental parameters

in the Arabian Sea exclusive economic zone (EEZ) of Oman and their influence on

the distribution and abundance of C. nufar as well as spawning time of the species

were investigated to determine if there were consistent patterns that could be related

to the physico-chemical parameter variability of water through the survey cruises

conducted by the R.V. Mustaqila 1 during September 2007 – September 2008.

Many events take place in the reproductive life of fishes with clear periodicity,

including within-year, within-spawning season, within-lunar cycle, and within-day

patterns. The timing of events at each of these scales di f fers from species to

species and from location to location. For e x a m p l e , many species of reef

fishes congregate at reef passes to spawn during high tide (Shibuno, et al., 1993;

Hensley, et al., 1994; Domeier and Colin, 1997). It is a strategy of the fish to direct

spawning to a time when eggs and larvae a re ca r r i ed rapidly away from the

reef and its dependent high density plankton feed in g f i s h (Shibuno, et al.,

1993; Hensley, et al., 1994; Danilowicz, 1995). Ecological factors such as

predation, competition or food availability can influence the timing of spawning

(Johannes, 1 9 7 8 ; Norcross and Shaw, 1984). Alternatively, spawning time may

be dictated by physiology for synchronization in the population (Qasim, 1973).

During particular time of the year, t h e best conditions l i k e temperature and

salinity trigger the adults to build up body reserves that can be used

subsequently to elaborate mature gonads. Spawning in fish coincides with

environmental conditions suitable for survival and growth of eggs and larvae or

juveniles (Bye, 1984; Norcross and Shaw, 1984). Hence, even minor increase in the

4

water temperature due to global warming might impose constraints on the fish

spawning time. It is hoped that all the present study will help to understand the status

of the stock of C. nufar along the Omani coast to plan for sustainable harvest.

1.2 The study Area: Arabian Sea and Oman coast

The Sultanate of Oman is located in the North West Indian Ocean and is surrounded

by three seas, the Arabian Gulf and the Oman Sea in the north, and the Arabian Sea

in the south (Fig.1). Fisheries productivity is heavily influenced by the

oceanographic dynamics in the area. The region is dominated by the seasonal

monsoon winds, particularly the southwest monsoon, which generates upwelling of

nutrient rich bot tom waters to the surface that enhance productivity, particularly in

the northern part of the area. The other major feature likely to strongly influence

fish productivity and distribution is the seasonal development of oxygen

deficient layers in depths between 50 and 1000 m in which most fish species

cannot live(Wishner et al., 1998).

The area for this study was located in t h e Arabian Sea between the lat i tude

16º 33' N and 22º 21' N and longitude between 53º 09' and 59º 55' E. This

area is unique tropical basin in the world which has a semi-annual cycle (Bohm et

al., 1999; Kumar et al., 2001a; Weller et al., 2002) and the strongest annual

variability in water circulation (Esenkov et al., 2003).

5

Fig. 1. Sultanate of Oman geographical location

The Arabian Sea is one of the most complex marine regions of the world

(Richardson et al., 2006) and is influenced by seasonal variations in

conditions (Savidge et al., 1990).There are two different water masses in the

study area, which are characterized by strong upwelling during the SW monsoon

(May to September) accompanied by cloud cover. These conditions have been

confirmed by various investigations (Schott, 1983; Quraishee, 1984; Kindle, 2001;

Prasad, 2004). During upwelling w h i c h is more intense in July, sea water

temperature is reduced (Rao et al., 2005). The SW monsoon later reverses to the

6

north-easterly direction with moderate winds and clear skies from November to

February (Flagg and Kim, 1998).

During the SW monsoon strong currents and upwelling bring colder, less saline

and nutrient rich bottom water from about 500 m depth to the surface mixed

layer to compensate the loss of water in the upper 500 m layer (Shi et al.,

1999). These features are also capable of transporting nutrient rich cold water to

hundreds of kilometers offshore (Brink et. al., 1998). The effect of the monsoon on

the water temperature is well documented (Wishner et al. 1998; Lee et al., 2000,

Weller et al., 2002). Warm sea surface temperatures are typically seen offshore

during the SW monsoon period, with cooler, more recently upwelled water present

near-to-shore.

The oxygen minimum zone (OMZ) is a midwater zone of low oxygen that extends

from just below the mixed layer to more than 1000 m, in some areas with oxygen

concentration less than 0.1 ml l-1

(Morrison et al., 1999). Species survival might be

significantly influenced by the fluctuations of dissolved oxygen. That impacts the

species composition in the ecosystem followed by trophic pathways and productivity

changes (Ekau et al., 2010).

Occurrence of the OMZs in the study area is common (Morrison et al., 1995). The

reasons for the existence of the OMZs may be due to large scale local ox ygen

consumption rates from high productivity in surface waters, very slow movement

of decaying organic matter within the layer consuming most oxygen present, low

oxygen concentration in the waters entering the layer from the southern ocean

(Olson et al., 1993), or the lack of an opening to seas to the north (Morrison et

al., 1999).

While, small organisms are physiologically limited by dissolved oxygen levels less

than 0.1 ml l-1

(Morrison et al.1999), larger organisms, such as fish, are limited by

sl ightly higher levels around 0.3 ml l-1

(Ashjian et al., 2002). However, demersal

fish and crustaceans (motile organisms) were rarely found where oxygen

7

concentration was below 1.5 ml l-1

in “The Dead Zone” in the Gulf of Mexico

(Rabalais et al., 2002).

Fluctuations in the extent of the OMZs can lead to redistribution of populations

of species (John, 2004), reduced distribution (less habitat available) (Arntz et al.,

1988), reduced catch (Banse, 1984), shifting of demersal fishes into the pelagic

zone, direct mortality, forced migration, increased susceptibility to predation,

changes in food resources and disruption of life cycles (Rabalais et al., 2002). The

OMZs also serve as biogeographic barriers by limiting cross- slope movements of

populations (Rogers, 2000).

1.3.Aims of the study

o To understand the seasonal variation of the marine environmental

parameters in the Arabian Sea and their influence on the distribution

of C. nufar.

o To study the biological and population characteristics of C. nufar in

the Arabian Sea

o To find out whether there is any consistent spatial difference in the

timing of spawning of C. nufar in relation to environmental factors

o To support the assessment and management of the stock(s) of C.

nufar targeted commercially in the Arabian Sea.

8

2. Material and Methods

2.1 Sampling procedures for the Arabian Sea Survey

2.1.1. Resource Assessment Survey of the Arabian Sea Coast of Oman

During 2007 – 2008 the Ministry of Fisheries Wealth (MFW) Sultanate of Oman

conducted a survey to provide estimates of the fishable biomass of principal

demersal, small pelagic and mesopelagic fish resources off the Arabian Sea coast

of Oman for ongoing stock assessment of Omani fisheries, to guide

development and investment decisions. Five seasonal surveys with an average

duration of 47 days were completed in the project period using the RV Al

Mustaqila 1. The surveys were timed to ensure coverage of the main seasons,

with an overlap of one season, between August 2007 and September 2008

(Table 1). The specific timing of the surveys was designed to achieve a

reasonable seasonal coverage but to avoid the limitations on survey activity that

were likely, based on normal weather patterns, during the June-July part of the

SW monsoon period. As the period of one cruise overlapped with two subsequent

season, for presentation of oceanographic data, the seasons broadly clasiified as

shown in Table -1 were followed.

2.1.2. Survey area, design, stratification and station allocation

The defined area for the survey was the continental shelf in the 20–250 m depth

range from Ra’s al Hadd to the Yemen border southwest of Salalah (Fig.2).

The region of survey was divided into 4 major areas, the boundaries of which

were based on features where the shelf edge is at its narrowest. A two phase

stratified random survey design was adopted in order to achieve greatest precision

in surveys for mixed demersal species; fisheries resources (Francis 1981,1984). The

major 4 survey areas were further divided by depth to make 15 strata. As the

surveys progressed, the survey area was recalculated including areas of strata. Initial

stratum boundaries were defined from electronic copies of British Admiralty charts.

9

The depth contours considered from these charts were 20–50, 50–100, and, in

some areas, the 100–150 m depth ranges.

Phase 1 of each seasonal survey consisted of 100 random trawl stations allocated

to strata based on an average station density of about 1 station per 190 km2 of

trawlable area, or 1 station per 317 square km of the total area. A minimum of three

stations per stratum was sampled in phase 1 of each survey. Up to 20 phase 2 stations

were then directed to the strata with the most variable catch rates. Station

positions were selected randomly before each voyage with a minimum distance

between stations of 2 nautical miles (Fig. 2).

Trawl survey tows were carried out during daylight hours only. Care was taken to

ensure that trawls started after dawn and were completed by dusk to minimize

variations in catchability which might result from day/night variation in fish

reaction to the trawl. The target numbers of demersal trawl stations per survey

are given (Table 1).

Table 1. Details of survey period, demersal fish survey and CTD stations

Voyage

No.

Voyage period Season demersal

stations

CTD

station

1 17 Sep 2007 - 15 OctPost SW

monsoon101

215

2 1 Nov - 17 Dec 2007Autumn Intermonsoon

104253

3 29 Jan 2008 - 18 Mar NE monsoon 120 348

4 19 Apr - 10 Jun Spring Intermonsoon 123 319

51 Aug - 23 Sep 2008

Post SW monsoon122 256

Total 570 1391

10

Fig. 2. Survey area and stations in the Arabian Sea

2.1.3. Survey procedures and data collection

The R . V . Al Mustaqila 1 is 46 m length overall, has a beam of 12.5 m,

horsepower of 3602 and a displacement of 1745 tonnes. The trawl gear was rigged

and deployed in the same manner for all the demersal tows across the 5 surveys.

The 40 m cod-end selected for the demersal trawl survey was constructed of 4 mm

knotted nylon braid. The nominal inside mesh measurement was 40 mm. A series

of 3 x 20 meshes were measured using callipers at the beginning of the first survey,

when the cod-end was dry (i.e., had not been used). The cod-end was marked and

repeat measurements were made during the second survey to evaluate any

variation in mesh sizes. At each station, the trawl target distance was 2 nautical

11

miles at a speed over the ground of 3.5 knots. Towing speed and gear configuration

were maintained as constant as possible during all seasonal surveys. The trawl

doors were of Thyboron Type 7 capable of being used in midwater or on the

seafloor. The door weight and size were 1968 kg and 9.37 m2 respectively.

Measurements of door spread, headline height, and vessel speed were recorded

every 5 min during each tow.

Beside the fishery resources, data on physio-chemical parameters of the water in the

Arabian Sea were collected during the survey. Temperature, salinity, dissolved

oxygen and depth were recorded by CTD deployment after every trawl operation.

The maximum amount of line deployed on the CTD casts was 500 m. To measure

100% dissolved oxygen (DO) saturation, the CTD was deployed just below the

water surface on each cast for at least 1 minute or held in a holding tank with

constant surface water flow for at least 5 minutes at each station. Two different

modules of CTDs were used during the survey, XR-620 and XR-420. The first

module replaced the X R - 4 2 0 on t h e f i r s t cruise, when it was found t h a t

the XR-420 titanium casing caused temperature lag. The XR-420 was used after

station 142 on t h e t h i r d c r u i s e because the XR-620 failed.

A biological data collection program on C. nufar was undertaken during

the survey based on special request for the purpose of this study. These

data include fish weight recorded to the nearest 0.1 g, sex, fish total length

measured to the nearest 0.1 cm. The stages of gonadal maturity identified are given

in Annex 1.

12

2.2. Collection and analysis of C. nufar samples from landing sites

Random samples of C. nufar were collected from commercial catches landed by

different types of artisanal gears such as gillnets, handlines, traps and commercial

trawl nets on monthly basis between April 2005 and March 2007.

2.2.1. Age and growth

A total of 4132 fish were measured for their total length (TL) and fork-length (FL) to

the nearest 1 mm using a fish measuring board and rounded off to the nearest cm to

calculate the monthly size frequency distribution in the catches. The relationship

between the TL and FL was estimated by regression analysis.

For the estimation of length-weight relationships of C. nufar, the TL and total weight

(TW) of the fresh fish were used. While, the TL was measured to the nearest 1 mm,

the TW was recorded to the nearest 1 g using a top pan balance. The general

equation,

=

where, TW and TL are the total weight and total length respectively, and 'a' and 'b'

are the constants to be determined were fitted separately for males and females.

Analysis of covariance (ANCOVA) (Snedecor and Cochran, 1967) technique was

employed to test the significant difference if any, in the relationships between males

and females at 5% level.

2.2.1.1. Estimation of growth parameters using length – frequency data

A total of 4132 fish measured for their TL and the lengths were grouped into 2 cm

class intervals. The size range of the fish varied from 16 cm to 64 cm TL. To

estimate the von Bertalanffy growth function (VBGF) parameters (L∞, K and t0) the

equation,

13

= ∗ 1 − ∗( °)

was fitted using the LFDA version 5.0 of FMSP- Fish Stock Assessment Software

(Hoggarth et al., 2006). Three alternative fitting techniques such as Shepherd's

Length Composition Analysis (SLCA), Projection Matrix (PROJMAT) and

ELEFAN 1 with non-seasonal version were used to calculate VBGF parameters.

Also, the routine Powell-Wetherall technique available with the FMSP-software was

used to estimate L∞ and Z/K. Since the suitability of ELEFAN 1 technique is

suggested for tropical fish (Pitcher, 2000), the growth parameters estimated by

ELEFAN 1 technique were considered for further analysis of stock assessment.

Length at age was estimated from the plots of SLCA, PROJMAT and ELEFAN 1,

and by the empirical method of Froese and Binohlan (2000). Length at first capture

was estimated by plotting cumulative percentages of length against length classes.

2.2.1.2. Estimation of growth parameters using otolith

A total of 258 fish (159 females and 99 males) ranging in size from 16 to 66cm (TL)

was used for otolith based ageing. To estimate the mass of the otoliths, one of the

sagittae from each fish was weighed to the nearest 0.01g. To determine the fish age,

the internal structure of the otolith, including the primordium (core) was examined in

resin-embedded sections.

One otolith from each fish was embedded in small moulds (< 2cm) containing epoxy

resin (Brothers et al., 1983). Thin sections (300μm) of otoliths were made through

the nucleus along a transverse, dorsoventral plane with a Buehler Isomet low-speed

saw containing a diamond wafering blade. In order to have a polished face for

viewing, excess resin on the sectioned face of the otolith was removed using a

grinding wheel fitted with silicon carbide paper of different grit sizes (400 to 1200

grit) and flushed with water.

Each section of the otolith was mounted on a microscopic slide and observed at 10x

X 4x magnification using a compound microscope with transmitted light. All the

sectioned otoliths (n=258) displayed clear increments and rings were used to

determine the age of the fish. The term “opaque zone” refers to the area that

14

appeared milky under reflected light or dark under transmitted light in unstained

samples. In our study, terminology was based on that recommended by Morales-Nin

(1991).

The age of each fish was determined by counting the number of rings; i.e. pairs of

alternating opaque and translucent rings from the sectioned otoliths. Rings were

counted, without reference to fish length or date of capture, in the ventral lobe of the

sagittal otolith from the primordium to the otolith margin close to the ventral margin

of the Sulcus acusticus. All counts were made in the same way and repeated at least

three times, with a two-week interval between readings, to ensure consistency. For

each fish the third count was used to estimate age, since by this time considerable

experience had been gained in the interpretation of the rings and otolith structure.

The relationship between size and age was determined using the von Bertalanffy

Growth Function (VBGF) (von Bertalanffy, 1934). The outer edge of the otoliths

was examined on a monthly basis for the presence of either an opaque or hyaline

zone to establish whether these zones were deposited annually. The growth

parameters estimated were compared with earlier studies. Since, growth is not linear,

comparison of growth in two fish populations using L∞ and K may be misleading.

Hence, the overall growth performance index (Munro’s phi prime index, Ø’) for C.

nufar was calculated empirically (Munro and Pauly, 1983) using the formula,

(∅′) = log + 2 log ∞

where, K is expressed on annual basis and L∞ in cm.

15

2.2.2. Maturation and Spawning

For studying the maturation and spawning in C. nufar, a total of 1,329 specimens

collected during 2005-07 were used.

State of maturity of gonads was recognized by modifying the stages defined by the

International Council for Exploration of the Sea (Lovern and Wood, 1937) to six

stages of maturity key (I-Immature; II-Maturing 1; III-Maturing 2; IV-Mature; V-

Ripe/Running and VI-Spent) to suite the present study. The stages were recognized

both in females and males by examining the ovaries macroscopically and also by the

microscopic structure of the intraovarian eggs; whereas, in males macroscopic

structure of testes alone was considered (Annex 1). The fixed ovarian stages were

counter checked with the histological sections (Annex 1B).

To study the development of ova from immature to mature stage, 36 ovaries in

maturity stages I to VI were used. Samples of ova from anterior, middle and

posterior regions of both the lobes were examined. As there was no difference in the

size of ova from different parts of the ovary, ova were sampled from the middle

region of the ovary for ova diameter measurements. About 200 ova from each ovary

were measured for the diameters. The method of measurement of ova diameters was

similar to that of Clark (1934); Prabhu (1956) and Jayabalan (1986). Ova diameters

were measured using an ocular micrometer fitted to the eye piece of the microscope

and each ocular micrometer division (o.m.d) was equal to 14μ (1000 μ=1mm). As

the ova measuring up to 6 o.m.d. were present in large numbers in all the stages of

ovary indicating the general stock of eggs, they were not measured from stage II

onwards. Ova diameter data from ovaries of same stage of maturity were pooled and

were grouped into 3 o.m.d for plotting percentage frequency curves.

The spawning season was determined based on commercial catch and samples

collected during the R . V . Al Mustaqila 1 demersal trawl survey. For spawning

season based on commercial catch, monthly percentage occurrence of different

maturity stages of gonads, gonado-somatic index (GSI), hepato-somatic index (HSI)

and relative condition factor (Kn) were calculated and plotted. A comparison of

16

spawning of C. nufar was also made using the data on maturity stages of gonads

during various surveys.

The monthly gonado-somatic index (GSI) was calculated separately for males and

females adopting the formula,

= × 100

where, GW denotes the gonad weight (g) and GuW denotes gutted weight (g).

For the nutritional state of the fish, the monthly hepato-somatic index was calculated

as suggested by Busacker et al., (1990) using the formula,

= / × 100

where HW = the liver weight (g) and TW = the total weight (g) of fish.

The monthly relative condition factor, Kn was estimated to understand the condition

of the fish following Le Cren (1951) as,

= /

where TW = observed weight, aLb = calculated weight obtained from the length-

weight relationship.

For estimating length at first maturity (Lm), fish were grouped into 1 cm class

interval and gonads from stage-III onwards were considered as mature for

calculating the fraction of mature fish at different lengths. A logistic function was

fitted to the fraction of mature fish against length interval as suggested by King

(1995).

The logistic equation used was:

= 1/ 1 + − ( − )

where P = proportion mature fish in length class L,

r = the width of the maturity curve and

17

Lm = length at 50% maturity

Based on the batches of intraovarian eggs that formed modes in the advanced stages

of ovaries (mature, ripe and spent ovaries), the spawning frequency in individual fish

was determined (Zacharia and Jayabalan, 2007). Fecundity of females were

estimated gravimetrically from 27 ovaries of stage IV. The minimum and maximum

sizes of the fish used for estimation of fecundity ranged between 28 cm TL and 63.4

cm TL and the body weight ranged from 280 g to 3,730 g. The weight of the ovaries

used varied from 3.5 g to 185.91 g respectively. From the known weight of the ovary

preserved in 5% neutral formalin, a small portion of the ovary was removed and

weighed to the nearest 0.001g in an electronic microbalance and then kept in

'modified Gilson's fluid' (Simpson, 1951) for 4 days. The piece of the ovary was

taken to a counting chamber and all the mature eggs in the piece of the ovary were

counted under a binocular microscope. From the number of mature ova in the piece

of the ovary, the total number of mature ova was estimated using the formula,

Fecundity =Total weight of the ovary / Weight of the sample * Number of mature

ova in the sample

The relationship between the fecundity and variables like total length, body weight

and ovary weight was found out by the least square method,

=

where, F=fecundity, a = constant, X = variable (fish length, fish weight or ovary

weight) and b = correlation coefficient.

The sex-ratio was estimated as male to female ratio. To test the monthly and annual

sex-ratios for the expected ratio of 1:1, the technique of chi-square (X2) analysis was

used. =∑( )2

Where, O = observed number of males and females in each month

E = expected number of males and females in each month

18

2.2.3. Food composition and feeding intensity

For analysis of quantitative and qualitative estimation of food of fish, samples were

collected at random from the commercial catch. The gut content from 775 specimen

during 2005-06 and 550 fish during 2006-07 were analysed. However, some bias

might have been introduced while sampling the fish for food and feeding habits as

the fish are targeted by handlines and trap fishery using baits, besides gillnets and

trawl nets.

For the general food items found in the gut, they were identified up to group level.

When the food item was in advanced state of digestion, it was recorded as

‘semidigested matter’. For the seasonal variation of the quantity of food items, points

(volumetric) method (Hynes, 1950) was used.

Feeding intensity in C. nufar was studied from September 2005 to March 2007. A

total of 990 fish were analyzed for the fullness of the stomachs and were grouped

into actively fed (full and 3/4 full stomachs), moderately fed (1/2 full stomachs),

poorly fed (1/4 full stomachs) and empty. The feeding intensity in relation to months,

maturity stages and size of the fish was estimated.

19

2.2.4. Population dynamics and stock assessment

The instantaneous total mortality rate (Z) of C. nufar was estimated by the length-

converted catch curve method (Pauly, 1983) and Beverton-Holt method (Beverton

and Holt, 1956) using the routines provided in the LFDA version 5.0 of FMSP

software. Adopting the Powell-Wetherall technique, L∞ and Z/K of C. nufar were

also calculated.

Natural mortality coefficient (M) of C. nufar was estimated by three different

empirical methods (Rikhter and Efanov 1976; Pauly, 1980; Alagaraja 1984) and the

average M was taken for further analyses.

In the empirical method of Pauly (1980), the following equation was adopted.

ln = −0.0152 −0.279 ∗ ln ∞ + 0.6543 log∗ + 0.4634 ∗ ln

where ‘T’ indicates the annual mean temperature (oC) of the surrounding water in

which the fish lives. In the present study, the T value was taken as 24°C as this value

represented the mean bottom water temperature in the Arabian Sea off Oman

(Thangaraja, 1995).

In Rikhter and Efanov's method (1976), the following formula was adopted

= 1.521/ 0.72 − 0.155

where, tm = the age at which 50% of the population matures.

Alagaraja's (1984) method assumes that 99% of a cohort had died, if it had been

exposed to natural mortality only. The formula used was:

1% = − ln(0.01)/

Where Tm indicates longevity and M1% indicates natural mortality corresponding to

1% survival.

20

Fishing mortality coefficient (F) was obtained by subtracting natural mortality (M)

from total mortality (Z) as,

= −

The term standing stock refers to the concentration of fish population for a given

area at a given time. This can be estimated in terms of numbers or weight. In this

study, the standing stock was estimated by weight using the formula,

= /

where Y is the yield and F, the fishing mortality

The total stock or biomass in weight was estimated using the relation between yield

and exploitation ratio as

= /

where Y is the annual yield and U is the exploitation ratio.

The maximum sustainable yield (MSY) was calculated by the equation suggested by

Cadima (in Traodec, 1977). Cadima's estimator used was,

= 0.5( + )

where Y is the total catch in a year, is the average biomass in the same year and M

the natural mortality. The MSY was also estimated using the ‘Yield’ software

(Hoggarth et al., 2006).

The exploitation rate (E) of C. nufar was estimated as suggested by Sparre and

Venema (1992) using the formula,

= / , where, E= the exploitation rate; F= the fishing mortality and Z=

total mortality. The exploitation ratio was calculated by the equation given by Ricker

(1975) as,

= / (1 − ) ,

21

where, U= the exploitation ratio; F= the fishing mortality and Z= total

mortality

Per-recruit analyses were made using routine available with the 'Yield' package

incorporated in the FMSP Software (Hoggarth et al., 2006). Estimations of

equilibrium yield-per-recruit (Yw/R), total biomass-per-recruit (TB/R) and stock

spawning biomass-per-recruit (SSB/R) were made for a range of F-values of C.

nufar. All the input parameters used for “Yield” software were obtained from the

present study.

The optimum length of exploitation was estimated empirically from the equation

(Froese and Binohlan, 2000) as,

= 3 ∗ ∞/3 + /

Where Lopt denotes the optimum length of exploitation, L�, the asymptotic length,

M, the natural mortality and K, the growth coefficient.

22

3. Result

3.1. Seasonal distribution of physico-chemical characteristics of waters of the

Arabian Sea

Temperature

Generally the sea surface water temperature was found to be warm that ranged

between 25 and 28 ºC during the autumn inter-monsoon period (Sept– Dec) that cooled

after the NE monsoon period (Feb) to 22 ºC – 24 ºC and warmed again to 25 ºC – 28

ºC during the spring inter-monsoon period (Apr–Jun). The water became very cool

(18-24 ºC) immediately after the SW monsoon (Figs. 3-7). In the Gulf of Masirah

area, the surface sea water was comparatively cooler by several degrees (up to 5˚C)

than in the waters in the southwest after the SW monsoon period (Sept) in 2007 (Fig.

3). However, during the autumn inter-monsoon period (Nov–Dec), the sea surface

water temperature did not fluctuate very much in the entire Arabian Sea area (Fig. 4).

Sea surface water temperatures within Salalah area were comparatively warmer than

in other areas during spring inter-monsoon 2008 (Fig. 6).

Fig. 3. Post- SW monsoon 2007: Sea surface temperature

23

Fig. 4. Autumn inter- monsoon 2007: Sea surface temperature

Fig. 5. NE monsoon 2008: Sea surface temperature

24

Fig. 6. Spring Inter- monsoon 2008: Sea surface temperature

Fig. 7. Post- SW monsoon 2008: Sea surface temperature

25

The nearshore (20–50 m strata) bottom temperatures were highest during the autumn

inter-monsoon period 25 ºC that subsequently reduced gradually as the surveys

progressed (Figs. 8–14). Bottom water temperatures in the entire area surveyed in the

Arabian Sea area were at their lowest 17 ºC immediately after the SW monsoon (Fig.

12). During 2008, the survey in the post-SW monsoon period was conducted nearly

two months earlier than in 2007. This may be the reason for the higher water

temperatures recorded during the post-SW monsoon period in 2007 (Fig. 8). Along the

shelf edge in the entire survey area, the bottom water temperatures were consistently

low.

Fig. 8. Post- SW monsoon 2007: Bottom temperature

26

Fig. 9. Autumn Inter-monsoon 2007: Bottom temperature

Fig. 10. NE monsoon 2008: Bottom temperature

27

Fig. 11. Spring Inter-monsoon 2008: Bottom temperature

Fig. 12. Post- SW monsoon 2008: Bottom temperature

28

Salinity

The sea surface water salinity did not vary much throughout the surveys (Figs. 13–16)

that ranged between 36 and 37 ppt. However, immediately after the SW monsoon

period in 2008 drastic changes occurred, 34 ppt, (Fig. 17). The salinity values of the

waters south of Masirah Island immediately after the SW monsoon in 2008 were low

(34-35 ppt); although, in certain areas on the shelf more saline waters occurred. The

reason for variability in sea surface salinity after the SW monsoon in 2008 might be the

effect of upwelling that brought colder, less saline waters upon to the shelf. The sea

surface water salinity in the area south of Masirah Bay had reverted back to the average

salinity of approximately 36 ppt during post SW monsoon 2007 (Fig. 13).

Fig. 13. Post- SW monsoon 2007: Surface salinity

29

Fig. 14. Autumn monsoon 2007: Surface salinity

Fig. 15. NE monsoon 2008: Surface salinity

30

Fig. 16. Spring Inter-monsoon 2008: Surface salinity

Fig. 17. Post- SW monsoon 2008: Surface salinity

31

The bottom water salinity showed similar pattern to surface salinity (Figs. 18–22). The

occurrence of less saline water, (33–35 ppt), was evident immediately after the SW

monsoon period in entire shelf south of Masirah Island (Fig. 22). During SW monsoon,

the bottom waters in the southern stratum (Areas 3 and 4) became more saline, 36 ppt,

(Fig. 18). The bottom water salinity was almost uniform throughout the survey area by

autumn monsoon 2007 (Fig.19).

Fig. 18. Post- SW monsoon 2007: Bottom salinity

32

Fig. 19. Autumn monsoon 2007: Bottom salinity

Fig. 20. NE monsoon 2008: Bottom salinity

33

Fig. 21. Spring Inter-monsoon 2008: Bottom salinity

Fig. 22. Post- SW monsoon 2008: Bottom salinity

34

Dissolved oxygen

Generally, the dissolved oxygen was high (4–6 ml l-1

) throughout the survey area.

Though, the oxygen minimum zone (OMZ) was recorded in the nearshore waters in

much of the survey area during the post SW monsoon period 2007; layers of well-

oxygenated waters were present in certain pockets located in Sawqirah Bay at depths

of 20–100m (Fig. 23). During this period as the oxygen sensor failed, measurements of

dissolved oxygen could not be carried out for the southern half of the survey area.

After the NE monsoon period (Jan–Mar), the extent of the OMZ got altered (Fig. 24).

The OMZ was not present in shallower waters, but was shifted to near the shelf edge

and close to the Oman– Yemen border. The OMZ was present much deeper, at depths

of 150-200 m.

Fig. 23. Post SW monsoon 2007: Bottom dissolved oxygen

35

Fig. 24. NE monsoon 2008: Bottom dissolved oxygen

During the spring inter-monsoon period (April–June), the concentration of dissolved

oxygen was low in the bottom waters, 0.1 – 1 ml l-1

almost in the entire survey area

(Fig. 25). In certain areas close to the shore and in south of Masirah Island, high

oxygenated bottom waters existed. Though, the well oxygenated nearshore bottom

waters occurred south of Masirah Island soon after the SW monsoon period, in certain

pockets of shallow areas (40-50 m) on the shelf, oxygen poor waters (up to 0.3 ml l-1

)

were present (Fig. 26).

36

Fig. 25. Spring inter-monsoon 2008: Bottom dissolved oxygen

Fig. 26. Post- SW monsoon 2008: Bottom dissolved oxygen

37

3.2. Study of C. nufar

Biomass and distribution of C. nufar in the Arabian Sea

Cheimerius nufar occurred throughout the survey area, but more commonly to the

south of Masirah Island, and predominantly in waters shallower than 100 m depth (Fig.

27). Total survey biomass (tonnes) of C. nufar and coefficients of variation (CVs) are

given Table 2. Estimates range from 1321 t in voyage 5 to 4598 t in voyage 3.

Lakbi bay had the highest estimates of biomass during voyages 1, 2, 3 and 4; while,

Salalah area estimates were highest on voyage 2 and 3. The 20–50 m depth range

held the highest biomass for all voyages; and the 100 - 150 m depth range produced

lowest biomass during voyages 1, 2 and 5 (Fig. 28).

Table. 2 Estimated biomass (t) and coefficients of variation (%, below in parentheses) for C

.nufar.

Voyage 1 Voyage 2 Voyage 3 Voyage 4 Voyage 5 Average

1513 3022 4598 2251 1321 2,541 t

(33) (31) (35) (17) (27)

38

Fig. 27. C. nufar distribution from all trawl survey stations

Fig. 28. Biomass of C. nufar in different depth zones in the Arabian Sea survey

0

250

500

750

1000

1250

1500

1750

2000

Voyage 1 Voyage 2 Voyage 3 Voyage 4 Voyage 5

Biom

ass

( t)

20 – 50 m

50 – 100 m

100 – 150 m

150 – 250 m

39

3.2.1. Age and growth estimation

In the present study, the estimations of age and growth of C. nufar were made using

two different techniques, the length frequency analysis and the interpretation of

growth marks on otoliths

Length frequency distribution

The size frequency distribution of C. nufar in the commercial catches ranged from

16 cm to 64 cm of TL during 2005-06 and during 2006-07, the size was ranged

between 18 cm and 64 cm of TL. During 2005-06, fish measuring up to 26 cm

formed about 32% of the catches. However, individuals in the size range of 28 cm -

30 cm formed about 33% of the catches and the rest of the higher sized fishes

collectively formed about 35% of the catches (Fig. 29). This trend changed to 26%,

23% and 51% respectively during 2006-07 (Fig. 30). The size frequency of the

pooled data for both the years is given in Fig. 31.

Fig. 29. Length frequency distribution of C. nufar in the commercialcatches during 2005-06

0

2

4

6

8

10

12

14

14 18 22 26 30 34 38 42 46 50 54 58 62

%

TL(cm)

N=1996

40

Fig. 30. Length frequency distribution of C. nufar in the commercial catchesduring 2006-2007

Fig. 31. Pooled length frequency distribution of C. nufar in the commercial catches

during 2005-2007

0

2

4

6

8

10

12

14

14 18 22 26 30 34 38 42 46 50 54 58 62

%

TL(cm)

N=2136

0

2

4

6

8

10

12

14

14 18 22 26 30 34 38 42 46 50 54 58 62

%

TL(cm)

N=4132

41

Total length-Fork length relationship

The relationship established between the total length and the fork length of the fish

can be expressed as, FL = 0.892TL-0.151 (R2=0.991) (Fig. 32)

Fig. 32. Total length-fork length relationship in C. nufar

Length-weight relationship

The estimated length-weight relationships of males, females and sexes pooled data of

C. nufar are shown in Table 3.

Table 3. Length – weight relationship parameters

Sex LW Confidence interval Sa Sb

MaleW = 0.018*L 2.907

(R2 = 0.986)

a: -0.033 – 0.071

b: 2.872 – 2.940

0.02650 0.01736

Female W = 0.020*L2.890

(R2 = 0.985)

a: - 0.028 – 0.068

b: 2.859 – 2.921

0.02439 0.01595

PooledW = 0.019*L2.897

(R2 = 0.985)

a: -0.016 – 0.055

b: 2.874- 2.920

0.01795 0.01174

FL = 0.892TL - 0.151R² = 0.991

10

20

30

40

50

60

15 25 35 45 55 65 75

FL (c

m)

TL (cm)

N= 1,300

42

The ANCOVA test for length-weight relationships of males and females showed

both the slopes and means were not significantly different (P>0.05) and hence, the

common equation for the species would fit well (Fig. 33). The coefficient of

determination (R2) in males, females and sexes pooled could be highly correlated.

Fig. 33. Length-weight relationship in C. nufar.

Estimation of growth parameters using length frequency data

Figures 34 – 36 show the VBGF parameters of C. nufar estimated using the monthly

length frequency data for the period 2005-2007 by SLCA (Fig. 34), PROJMAT (Fig.

35) and ELEFAN (Fig. 36) techniques.

Fig. 34. VBGF curve of C. nufar by SLCA technique

W = 0.019L2.897

R² = 0.985

0

1000

2000

3000

4000

10 20 30 40 50 60 70

Tota

l wei

ght (

g)

Total length (cm)

0 0 . 5 1 . 0 1 . 5 2 . 0 2 . 50

1 0

2 0

3 0

4 0

5 0

6 0

7 0

S a m p l e Ti m i n g

Le

ng

th C

las

s

G r o w th C u r v e = N o n S e a s o n a l . L i n f = 7 0 . 3 5 . K = 0 . 3 1 . Tz e r o = -0 . 2 3 .

43

Fig. 35. VBGF curve of C. nufar by PROJMAT technique

Fig. 36. VBGF curve of C. nufar by ELEFAN 1 technique

0 0.5 1.0 1.5 2.0 2.50

10

20

30

40

50

60

70

Sample Timing

Leng

th C

lass

Growth Curve = Non Seasonal. Linf = 68.26. K = 0.25. Tzero = -0.55.

0 0.5 1.0 1.5 2.0 2.50

10

20

30

40

50

60

70

Sample Timing

Leng

th C

lass

Growth Curve = Non Seasonal. Linf = 70.97. K = 0.30. Tzero = -0.18.

44

The L∞ of C. nufar estimated by Powell-Wetherall technique was 65.27 cm. Though

there were variations in VBGF parameter values between different techniques (Table

4), the values obtained by ELEFAN 1 technique were used for subsequent stock

assessment.

Table.4. VBGF parameters of C. nufar estimated by different methods

Method L∞ (cm) K (y-1) t0 (y)

SLCA 70.35 0.31 -0.229

PROJMAT 68.26 0.25 -0.55

ELEFAN 1 70.97 0.298 -0.180

Powell-Wetherall 65.27 - -

Age distribution in commercial catches

The age distribution of C. nufar in the commercial catches (Fig. 37) indicated that

individuals belonging to the age groups 0-4 years supported the fishery.

45

Fig. 37. Age distribution of C. nufar in the commercial catches during 2005-

2007

Length at age

The lengths of C. nufar were converted into age using growth estimations by the

SLCA, PROJMAT and ELEFAN 1 techniques (Fig. 38). The SLCA indicated higher

lengths for all the ages followed by the ELEFAN 1 and PROJMAT techniques. The

lengths converted into age showed that the life span of C. nufar would be about 11

years in the Omani waters. The life span estimated by the equation 3/K (Pauly,

1983a) indicated that the fish may live up to 10.5 years.

0 0.5 1.0 1.5 2.0 2.50

2

4

6

8

Sample Timing

Nom

inal

Age

Age Slice

46

Fig. 38. Growth curves derived from length frequency analyses in C. nufar

Length at capture and recruitment

In the commercial catches, the smallest fish encountered measured 16 cm of TL and

the largest fish measured 64 cm TL. The length at 50% of fish caught (Lc) was

calculated to be 31.4 cm (Fig. 39). The maturity in both males and females appeared

to attain at the beginning of third year.

Fig. 39. Length at first capture of C. nufar

15

25

35

45

55

65

75

1 2 3 4 5 6 7 8 9 10 11

Tot

al le

ngth

(cm

)

Age (y)

SLCAPROJMATELEFANAverage

0102030405060708090

100

15 20 25 30 35 40 45 50 55 60 65 70

Prob

ablit

y of

cap

ture

TL(cm)

Lc=31.4 cm

47

Estimation of growth parameters using otoliths

Periodicity of ring formation

A section through the otolith of a 13 year old C nufar is shown in Fig. 40. The

distance between the growth rings can be seen to narrow with increasing age.

Fig. 40. Photomicrograph of a transverse section through the sagittal otolith.

A total number of 258 sectioned otoliths were read. The rings were clearly visible

and the age of the fish could be determined in most of them. A definite seasonal

variation in the formation of opaque and hyaline zones is evident on the otolith edge

(Fig.41). Hyaline zone formation takes place from March – June and the opaque

zones are laid down from July – January. It can therefore be concluded that one

opaque zone and one hyaline zone are formed annually.

48

Fig. 41. Monthly percentage of otoliths with hyaline and opaque edge.

Size at age and growth

The VBGF curves were fitted to lengths-at-age for C. nufar (Table 5, Fig. 42). The

age estimation indicates the life span is 13 years. The VBGF suggests that the male

fish had a higher growth rate when younger and attained a smaller theoretical

maximum size than females. In the age – length key, a wide range of lengths (24 –

64 cm) within most age groups was found (Table 6 A, B, C & D).

0

10

20

30

40

50

60

70

80

90

100

J F M A M J J A S O N D

%

Months

Opaque

Hyaline

49

Table 5. Growth parameters of male and female C. nufar using otolith reading.

Sex L∞ K to r2

Male 66.47 0.1939 -0.36055 0.89652

Female 69.77 0.182 -0.24886 0.92528

Fig. 42. VBGF curves for C. nufar, Female (n =159) and Male (n =99).

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14

Size

(cm

)

Age(y)

Male - Data

Female - Data

M - VBG

F-VBG

50

Table 6 A. Age - length key for Male of C. nufar - sectioned otolith.

TL(cm)Age (y)

Total1 2 3 4 5 6 7 8 9 10 11 12 13

16 2 2

18 6 6

20 4 4 8

22 7 7

24 1 2 3

26 3 3

28 5 5

30 4 4

32 2 1 3

34 1 1

36 4 4

38 3 3

40 5 5

42 3 5 1 9

44 1 3 4

46 1 3 1 5

48 1 1 1 3

50 1 1 1 1 1 5

52 2 1 1 4

54 1 1 1 3

56 1 1

58 1 1

60 1 1

62 2 3 1 6

64 1 1 2

66 1 1

Total 12 12 16 18 13 6 3 5 4 2 2 4 2 99

51

Table 6 B. Age - length key for female of C. nufar - with sectioned otolith.

TL(cm)Age (y)

Total1 2 3 4 5 6 7 8 9 10 11 12 13

18 5 5

20 2 10 12

22 6 6

24 1 1 2

26 3 3

28 2 1 1 4

30 3 1 4

32 1 1 2

34 4 4

36 7 3 10

38 13 13

40 5 5

42 1 1 2

44 1 1 2

46 1 1 2

48 1 1 1 1 4

50 1 1 1 1 2 6

52 9 1 2 2 14

54 2 1 3 1 7

56 3 2 5

58 3 3

60 4 3 4 4 15

62 3 3 4 10

64 5 5 8 18

66 1 1

Total 7 17 10 33 8 13 6 8 11 8 11 14 13 159

52

Table 6 C. Age structure of C. nufar population in the Arabian Sea.

TL(cm) Age (y) Male Total

1 2 3 4 5 6 7 8 9 10 11 12 13

16 9 9

20 10 43 53

24 59 267 325

28 362 52 26 440

32 139 277 46 462

36 283 32 315

40 105 45 8 158

44 12 31 18 12 6 80

48 8 8 8 8 2 5 8 45

52 1 9 2 2 1 2 2 21

56 3 2 4 1 9

60 3 6 2 2 3 3 19

64 1 5 5 4 14

Total 19 102 767 730 189 35 30 20 12 11 15 14 8 1951

53

Table 6 D. Age structure of C. nufar population in the Arabian Sea

Growth performance index (phi-prime index)

While the growth performance index (Ø’) based on length frequency data was

estimated at 3.14, the otolith based estimates of K and L∞ gave a value of 2.945.

TL(cm) Age (y) Female Total

1 2 3 4 5 6 7 8 9 10 11 12 13

16 11 11

20 11 49 60

24 66 298 365

28 405 58 29 492

32 155 310 52 517

36 318 35 353

40 118 50 8 176

44 14 35 21 14 7 90

48 8 8 8 8 3 5 8 50

52 2 11 3 3 1 3 3 24

56 3 2 4 1 11

60 3 7 2 3 3 3 21

64 1 5 5 4 16

Total 22 115 859 817 211 40 33 22 14 12 16 15 8 2185

54

3.2.2. Maturation and Spawning

The maturity key for the identification of different stage of gonads in males and

females of C. nufar is given in Annex 1A. The results of the histological assessment

of the stages of ovarian development in female C. nufar are shown in Annex 1B,

which show the various stages present during the spawning season, (i.e. immature,

maturing, mature and ripe stages).

Development of ova to maturity

Diameters of intraovarian eggs from stages I to VI ovaries studied to understand the

process of development of ova from immature to ripe for spawning are given in (Fig.

43 A-F & Annex 1). In stage-I, ova measuring 0.014-0.042 mm formed the mode

and several ova measured up to 0.098-0.126 mm. These ova may be considered as

the general egg stock. In stage-II, a batch of ova forming mode at 0.224-0.252 mm

got separated from the general egg stock for further development. Few larger ova

measured up to 0.308-0.336 mm. In stage-III, ova with two modes close to each

other (0.226-0.229 mm and 0.350-0.378 mm) were present and the maximum size of

ova measured up to 0.462 mm. Both the batches of eggs were in maturing condition.

In stage- IV, the mode formed by ova of 0.266-0.294 mm in stage-III was stationary

and an additional advanced mode at 0.434-0.462 mm was evident and this mode

represented the mature group of eggs. However, in this stage few ova were larger

and measured up to 0.546 mm. In stage V, the mature group of ova forming mode at

0.434-0.462 mm. In stage IV further developed and formed the mode at 0.770-0.798

mm. This mode represented the ripe eggs. In stage-VI, ripe ova (mode at 0.770-0.798

mm in stage V) were absent indicating that the ripe ova were shed during spawning.

The maturing group of ova forming mode at 0.266-0.294 mm was present and few

larger disintegrating eggs were also seen. The batch of ripe ova (0.770-0.798 mm)

present in stage V ovary was absent in spent ovary and few larger ova were in the

state of resorption (Fig. 43). This shows that the ripe eggs had released during

spawning. The intermediate stage of maturing group of ova (mode at 0.266-0.294

mm) present in spent ovary would take probably half the time than the immature ova

55

to attain ripe stage for spawning. Hence, it appears that individual fish would spawn

more than once during the spawning season in Arabian Sea.

Fig. 43 A. Development of ova to maturity stage I in C. nufar

Fig. 43 B. Development of ova to maturity stage II in C. nufar

0

25

50

75

1000.

014-

0.04

20.

056-

0.08

40.

098-

0.12

60.

140-

0.16

80.

182-

0.21

00.

224-

0.25

20.

266-

0.29

40.

308-

0.33

60.

350-

0.37

80.

392-

0.42

00.

434-

0.46

20.

476-

0.50

40.

518-

0.54

60.

560-

0.58

80.

602-

0.63

00.

644-

0.67

20.

686-

0.71

40.

728-

0.75

60.

770-

0.79

8

%

Ova diameter (mm)

A I

0

20

40

60

0.01

4-0.

042

0.05

6-0.

084

0.09

8-0.

126

0.14

0-0.

168

0.18

2-0.

210

0.22

4-0.

252

0.26

6-0.

294

0.30

8-0.

336

0.35

0-0.

378

0.39

2-0.

420

0.43

4-0.

462

0.47

6-0.

504

0.51

8-0.

546

0.56

0-0.

588

0.60

2-0.

630

0.64

4-0.

672

0.68

6-0.

714

0.72

8-0.

756

0.77

0-0.

798

%

Ova diameter (mm)

B II

56

Fig. 43 C. Development of ova to maturity stage III in C. nufar

Fig. 43 D. Development of ova to maturity stage IV in C. nufar

Fig. 43 F. Development of ova to maturity stage V in C. nufar

0

10

20

30

0.01

4-0.

042

0.05

6-0.

084

0.09

8-0.

126

0.14

0-0.

168

0.18

2-0.

210

0.22

4-0.

252

0.26

6-0.

294

0.30

8-0.

336

0.35

0-0.

378

0.39

2-0.

420

0.43

4-0.

462

0.47

6-0.

504

0.51

8-0.

546

0.56

0-0.

588

0.60

2-0.

630

0.64

4-0.

672

0.68

6-0.

714

0.72

8-0.

756

0.77

0-0.

798

%

Ova diamater (mm)

C III

0

5

10

15

20

0.01

4-0.

042

0.05

6-0.

084

0.09

8-0.

126

0.14

0-0.

168

0.18

2-0.

210

0.22

4-0.

252

0.26

6-0.

294

0.30

8-0.

336

0.35

0-0.

378

0.39

2-0.

420

0.43

4-0.

462

0.47

6-0.

504

0.51

8-0.

546

0.56

0-0.

588

0.60

2-0.

630

0.64

4-0.

672

0.68

6-0.

714

0.72

8-0.

756

0.77

0-0.

798

%

Ovadiameter (mm)

D IV

0

5

10

15

0.01

4-0.

042

0.05

6-0.

084

0.09

8-0.

126

0.14

0-0.

168

0.18

2-0.

210

0.22

4-0.

252

0.26

6-0.

294

0.30

8-0.

336

0.35

0-0.

378

0.39

2-0.

420

0.43

4-0.

462

0.47

6-0.

504

0.51

8-0.

546

0.56

0-0.

588

0.60

2-0.

630

0.64

4-0.

672

0.68

6-0.

714

0.72

8-0.

756

0.77

0-0.

798

0.81

2-0.

840

%

Ova diameter (mm)

F V

57

Spawning Season

Spawning Season based on commercial catch Data

The monthly percentage occurrence of different stages of maturity of ovaries and

testes for 2005-06 and 2006-07 (Figs. 44, 45) showed the ripe gonads (stage V) to

occur from April to September during 2005-06 and 2006-07. However, the spent

gonads were recorded only for three months (June, September and October) during

2005-06 and four months (June, August-October) during 2006-07. Occurrence of

spent individuals in June may contain few fish that spawned during the later part of

May and occurred during June in the catches. Similarly, spent fish recorded in

October 2005 and 2006 might be due to the spawning in some fish during later part

of September and recorded in October. The presence of spent fish in the commercial

catches during June to October shows that C. nufar may spawn for about 6 months

(May-October) and peak spawning may be between June and September in Omani

waters.

Spawning Season based on Survey Data

Spawning observation

The period of spawning of C. nufar is likely to occur during the SW monsoon as the

gonads in running ripe stage occurred almost exclusively in the post sw monsoon

2007/2008 in Area2, Area 3 and Area 4, which coincided with lower value of water

temperatures, 18 Cº – 23 Cº, in the entire area of the Arabian Sea that took place

immediately during the SW monsoon (Fig. 3, Fig. 7, Fig. 46 A & B).

58

Fig. 44. Distribution of different maturity stages of gonads of C. nufar

during 2005-06

0

25

50

75

I II III IV V VI

Perc

enta

ge M (n=19)F (n=24)

Apr 05

0

25

50

I II III IV V VI

Perc

enta

ge

M (n=29)F (n=16)

May

0

25

50

I II III IV V VI

Perc

enta

ge M (n=35)F (n=46)

June

0204060

I II III IV V VI

Perc

enta

ge M (n=35)F (n=48)

July

020406080

I II III IV V VI

Perc

enta

ge M (n=33)F (n=42)

August

0

20

40

I II III IV V VI

Perc

enta

ge

Maturity stages

M (n=38)F (n=34) September

0

20

40

60

I II III IV V VI

Perc

enta

ge M (n=17)F (n=24)

October

020406080

I II III IV V VI

Perc

enta

ge

M (n=32)F (n=47)

November

0

50

100

I II III IV V VI

Perc

enta

ge M (n=31)F (n=40)

December

0

50

100

I II III IV V VI

Perc

enta

ge

M (n=31)F (n=40)

Jan 06

0

20

40

60

I II III IV V VI

Perc

enta

ge

M (n=22)F (n=24)

February

0

50

100

I II III IV V VI

Perc

enta

ge

Maturity stages

M (n=25)F (n=25)

March

59

Fig. 45. Distribution of different stages of gonads of C. nufar during 2006-07

0255075

100

I II III IV V VI

Perc

enta

ge M (n=24)F (n=16)

April 06

0

20

40

60

I II III IV V VI

Perc

enta

ge

M (n=20)F (n=20)

May

0

20

40

60

I II III IV V VI

Perc

enta

ge

M (n=55)F (n=65)

June

0

20

40

60

I II III IV V VI

Perc

enta

ge

M (n=16)F (n=24) July

0

20

40

60

I II III IV V VI

Perc

enta

ge

M (n=20)F (n=33)

August

0

20

40

60

I II III IV V VI

Perc

enta

ge

Maturity stages

M (n=20)F (n=22) September

0

20

40

60

I II III IV V VI

Perc

enta

ge M (n=30)F (n=21)

October

0204060

I II III IV V VIPe

rcen

tage

M (n=19)F (n=22)

November

020406080

I II III IV V VI

Perc

enta

geM (n=19)F (n=21)

December

0

50

100

I II III IV V VI

Perc

enta

ge M (n=12)F (n=28)

Jan 07

0

50

100

I II III IV V VI

Perc

enta

ge

M (n=26)F (n=12)

February

0

50

100

I II III IV V VI

Perc

enta

ge

Maturity stages

M (n=19)F (n=19)

March

60

Fig. 46 - A. Fish with running ripe maturity stage during post SW monsoon

2007

Fig. 46 - B. Fish with running ripe maturity stage during post SW monsoon

2008

61

The sex-wise monthly gonado-somatic indices of C. nufar for 2005-2007 (Figs. 47)

clearly indicated that females always recorded higher GSI than males. The GSI

values were higher in females than the weighted average (0.65) during July and

August. For males, the GSI values were higher during May, July, August, September

and October than the weighted annual average (0.281). The higher GSI values during

June-September coincided with sw monsoon season which was the peak spawning

season of C. nufar. The peak spawning activity of fish occurred when the water

temperature declined to 23 -25 ºC during the above months (Fig. 47).

Fig. 47. Monthly gonado-somatic indices in C. nufar 2005 – 2007

The calculated monthly hepato-somatic indices of female fish registered generally

higher values than the males except February and March during 2005-2007 (Fig.48).

The peak value for both males and females were during September which started

declining progressively up to February. The declining trend of HSI values from

September to February was almost identical to the declining trend of GSI values.

22

23

24

25

26

27

28

29

30

0

0.5

1

1.5

2

2.5

A M J J A S O N D J F M

GSI

Months

Female

Male

Temp

62

Fig. 48. Monthly hepato-somatic indices in C. nufar 2005 -2007

During 2005-07, while the monthly relative condition factor (Kn) values (Fig. 49) for

males ranged from 0.98 (August) and 1.27 (February), the values for females

fluctuated between 0.96 (June) and 1.19 (February). The weighted average for males

was 1.079 and for females was 1.023. In males higher Kn were recorded than the

weighted average during September, October, December and February. While for

females the weighted average was 1.023 and values were higher than the average

during September, October, December and February.

In general, males registered better condition values than the females during various

months. The average monthly Kn for 2005-2007 indicated rise and fall in the values

and hence, could not be related to spawning.

0.6

0.8

1

1.2

1.4

1.6

1.8

April

May

June July

Augu

st

Sept

embe

r

Oct

ober

Nov

embe

r

Dece

mbe

r

Janu

ary

Febr

uary

Mar

ch

HSI

Female

Male

63

Fig. 49. Monthly Kn in C. nufar 2005-2007

Occurrence of juveniles in survey areas

Juveniles of the species were found throughout the survey area, although most

commonly in the three southern Zones (Fig.50-54).

Fig. 50.Juveniles distribution -Post SW monsoon 2007

0.9

0.95

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

A M J J A S O N D J F M

Kn

Months

FemaleMale

64

Fig. 51 Juveniles distribution: Autumn monsoon 2007

Fig. 52 Juveniles distribution –NE monsoon 2008

65

Fig. 53 Juveniles distribution Spring Inter-monsoon 2008

Fig. 54 Juveniles distribution -Post SW monsoon 2008

66

Length at first maturity

Males measuring less than 21 cm TL and females measuring less than 23 cm

were all immature. The percentage of mature individuals of both the sexes increased

with increase in length of the fish. The length at 50% of maturity in males and

females were estimated at 33.7 cm and 31.9 cm of TL respectively (Fig.55). This

indicates that the females mature at an earlier length than males.

Fig. 55 Length at first maturity in C. nufar

Fecundity

In C. nufar, the batch fecundity varied between 11,406 and 473,277 (Annex 2).

There was general increase in fecundity as the length, body weight and gonad weight

of the fish increased. The relationship between the fecundity (F) and total length of

fish (TL) (Fig. 56 A) was found to be,

F = 4.3232+0.0061 TL (R2 = 0.898)

0

0.2

0.4

0.6

0.8

1

10 15 20 25 30 35 40 45 50 55 60 65

Prop

ortio

n m

atur

e

Total length (cm)

MaleMaleFemaleFemale

Male: Lm = 33.7 cmFemale: Lm = 31.9 cm

67

The relationship between fecundity (F) and body weight (W) (Fig. 56 B) could be

expressed as,

F = 1.3938 + 4.3082 w (R2 = 0.9085)

The relationship between fecundity (F) and ovary weight (OW) (Fig. 56 C) was

estimated as,

F =0.9857 + 3074.1 OW (R2 = 0.9921)

Fecundity in C. nufar could be well correlated to the weight of the ovary than the

body weight and length of the fish as R2 =0.992.

Fig. 56 A. Fecundity in relation to total length (cm) of C. nufar.

y = 0.0061x4.3232

R² = 0.8977

0

50

100

150

200

250

300

350

400

450

500

20 30 40 50 60 70

Fecu

dity

('00

0)

Total length(cm)

A

68

Fig. 56 B. Fecundity in relation to body weight(g) of C. nufar .

Fig. 56 C. Fecundity in relation to ovary weight (g) of C. nufar

y = 4.3082x1.3938

R² = 0.9085

0

50

100

150

200

250

300

350

400

450

500

0 500 1000 1500 2000 2500 3000 3500 4000

Fecn

dity

('00

0)

Total Weight(g)

B

y = 3074.1x0.9857

R² = 0.9921

0

100

200

300

400

500

600

0 50 100 150 200

Fecu

ndity

('00

0)

Ovary Weight (g)

C

69

Sex- ratio

The percentage composition of male and female of C. nufar for different months is

shown in Fig. 57. As the sexes of the fish could not be identified externally, the fish

were dissected to recognize the sex. The monthly sex-ratio for the period April

2005–March 2006 (Table. 7A) and April 2006-February 2007 (Table. 7B) indicated

the overall dominance of females over males. However, the sex-ratios did not differ

significantly during both the years. The monthly sex-ratios during 2005-06 were not

significant at 5% level. During 2006-’07, among the monthly sex ratios, significant

difference was found only during January (x2=6.4) and February 2007 (x2=5.1578).

Fig. 57. Sex ratio of C. nufar during the period April 2005 - March 2007

0

10

20

30

40

50

60

70

80

Apr-

05M

ayJu

ne July

Aug

Sep

Oct

Nov De

cJa

n-06 Fe

bM

ar Apr

May

June July

Aug

Sep

Oct

Nov De

cJa

n-07 Fe

bM

ar

%

Months

Male

Female

70

Table. 7A Sex-ratio in C. nufar during 2005-06

M h

Total No.

f fi h

No. of

lNo. of females Male: Female Chi-square value

Apr 05 43 19 24 1:1.3 0.5814

May 45 29 16 1:0.6 3.7556

June 81 35 46 1:1.3 1.4938

July 83 35 48 1:1.4 2.0362

Aug 75 33 42 1:1.3 1.08

Sept 72 38 34 1:0.9 0.2222

Oct 41 17 24 1:1.4 1.1952

Nov 79 32 47 1:1.5 2.8482

Dec 71 31 40 1:1.3 1.1408

Jan 06 60 36 24 1:0.7 2.4

Feb 46 22 24 1:1.1 0.087

March 50 25 25 1:1 0

Total 746 352 394 1:1.1 2.3646

*Significant at 5% level

71

Table. 7B Sex-ratio in C. nufar during 2006 -07

*Significant at 5% level

Month Total No.

f fi h

No. of

lNo. of females Male: Female Chi-square value

Apr 06 40 24 16 1:0.7 1.6

May 40 20 20 1:1 0

June 120 55 65 1:1.2 0.8334

July 40 16 24 1:1.6 1.6

Aug 53 20 33 1:1.7 3.1886

Sept 42 20 22 1:1.1 0.0952

Oct 51 30 21 1:0.7 1.5882

Nov 41 19 22 1:1.2 0.2196

Dec 40 19 21 1:1.1 0.1

Jan 07 40 12 28 1:2.3 6.4*

Feb 38 26 12 1:0.5 5.1578*

March 38 19 19 1:1 0

Total 583 280 303 1:1.1 0.9074

72

3.2.3. Food composition and feeding intensity

Of the 775 specimens analyzed during 2005-06 and 550 fish studied during 2006-07

for food and feeding habits of C. nufar, 523 and 324 fish had empty stomachs during

the first year and second year of observation respectively.

The common food items found in the gut of C. nufar largely belonged to fishes

(sardine, anchovy, Therapon), crustaceans (crab, shrimp) cephalopods (cuttlefish,

squid, octopus) and polychaetes. Fish as food items of C. nufar contribute 50% and

57.96% during 2005-06 and 2006-07, followed by semidigested matter 42.9% and

39.4% respectively (Figs. 58 & 59). Rest of the food items were of minor importance

and polychaetes were recorded only during 2005-06.

Fig. 58. General food composition of C. nufar during 2005-06

50

2.382.781.98

42.86

Fish

Crustaceans

Cephalopods

Polychaete worms

Semidigested matter

73

Fig. 59. General food composition of C. nufar during 2006-07

Food Composition during different months

During 2005-06, the volume of fish as food items of C. nufar varied from 0%

(February) to 65.95% July (Fig. 60). While, the indices of semidigested matter

ranged between 23.4% (July) and 100% (January), the other food items such as

crustaceans (0% - 11.1%) and cephalopods (0% -10.5%) occurred for few months.

Polychaetes (6.9%) were recorded only during August.

During 2006-2007, semidigested matter was the dominant item in the gut of fish

during most of the months and the composition ranged between 10% (December)

and 88.9% (April) (Fig. 61). The contribution of fish as food item of C. nufar varied

from 11.1% (July) to 83.79% (October).

57.96

1.331.33

39.39

Fish

Crustaceans

Cephalopods

Semidigested matter

74

Fig. 60. Monthly percentage of composition of food items of C. nufar

during 2005-06

Fig. 61. Monthly composition of food items of C. nufar during 2006-07

60

25

42.11

65.9563.01

40

52.94

26.67

55.56

16.67 20

4.26 5.8811.11

6.6710.53 6.38 6.67 5.56

40

75

47.37

23.430.14

53.33

41.18

73.33

27.78

83.33

100

73.33

0

20

40

60

80

100

Apr 0

5

May

June July

Augu

st

Sept

embe

r

Oct

ober

Nov

embe

r

Dece

mbe

r

Jan

06

Febr

uary

Mar

ch

% c

ompo

sitio

n

Months

N=775FishCrustaceansCephalopodsPolychaete wormsSemidigested matter

11.11

36.8445

55.5556.75

73.0883.79

55.55

90

33.33

63.64

33.34

8.11 7.69 9.09

88.89

63.16 55

44.4435.14

19.23 16.22

44.44

10

66.67

27.27

66.67

0

20

40

60

80

100

Apr 0

6

May

June July

Augu

st

Sept

embe

r

Oct

ober

Nov

embe

r

Dece

mbe

r

Jan

07

Febr

uary

Mar

ch

% C

ompo

sitio

n

Months

N=550FishCrustaceansCephalopodsSemidigested matter

75

Food composition in different size of fish

For the food items found in the fish of different sizes, the data were pooled for 2005-

06 and 2006-07. The contributions of fish items and semidigested matter were

dominant in all the size groups (Fig. 62). However, the crustaceans were preferred in

minor quantities by size groups of 16-30 cm. Cephalopods and polychaetes were

preferred by small and medium sized fish.

Fig. 62. Food items found in the gut of various size groups of C. nufar

during 2005-2007 (pooled)

53.8559.46

48.8456.06

60.8765.86

71.43

50

75

50

15.39

2.7 2.3305.41 4.65 0.76 1.45

6.25

30.77 32.43

43.41 41.6736.23

31.71 28.57

43.75

25

50

0

20

40

60

80

100

16-2

0

21-2

5

26-3

0

31-3

5

36-4

0

41-4

5

46-5

0

51-5

5

56-6

0

61-6

5

% C

ompo

sitio

n

Size groups (TL-cm)

N=1325FishCrustaceansCephalopodsPolychaetesSemidigested matter

76

Feeding intensity in relation to month, maturity stage and size of fish

Of the 990 fish analyzed 668 had empty stomachs. The empty stomachs were

dominant during all the months excepting July, August and October 2006 (Fig. 63).

Active feeding (full and 3/4full stomachs) was found to range from 0% (February

2006) to 58.8% (October 2006) of individuals. Moderate feeding (1/2full stomach)

was observed from 0% (December 2005, January-February 2006) to 14.6%

(December 2006) of fish. Poor feeding intensity (1/4full stomach) was to vary from

0% to 24.4% and the highest percentage was recorded during January 2007.

Fig. 63. Feeding intensity in C. nufar relation to months

75

43

80

81

61

48

52

41

40

80

40

53

42

5141

41

41

40

40

0

20

40

60

80

100

Sept

05

Oct

Nov De

cJa

n 06 Fe

bM

arch Ap

rM

ay Jun Jul

Aug

Sept Oct

Nov De

cJa

n 07 Fe

bM

arch

Feed

ing

inte

nsity

(%)

Months

Empty1/4 full1/2 full3/4 fullFull

N=990

77

There was no consistency in the occurrence of active, moderate and poor feeding in

various stages of maturity of males and females (Fig. 64). However, empty stomachs

were dominant in all the maturity stages that ranged from 50% (stage IV) to 76%

(stage I) in males and 47.2% (stage VI) to 77.57% (stage I) in females.

Fig. 64. Feeding intensity in different maturity stages of C. nufar

7.23 9.3517.65 16.85 22.22 16.91 22.22 17.39

30.564.01 0.93

7.35 2.8114.29

5.155.56

4.3524.24

14.28

2.78

12.04 10.28

11.03 9.55

11.11

10.29

22.2217.39

25

24.2428.57

13.89

0

20

40

60

80

100

MI

F MII

F MIII

F MIV

F MV

F MVI

F

Feed

ing

inte

nsity

(%)

Maturity stages

Empty1/4 full1/2 full3/4 fullFull

M= male(n=477)

F= female(n=513)

78

Feeding intensity in relation to different sizes of C. nufar showed inconsistency of

feeding among fish (Fig. 65). The percentage of empty stomachs ranged from 55.6%

(51-55 mm size group) to 75% (41-45 mm size group). Active feeding was

observed in fish of sizes 61-65 mm (66.7%) and 71-75 mm (100%).

Fig. 65. Feeding intensity in different size groups of C. nufar

18.42 12.03 11.62 13.3623.47

13.8925 22.22

12.5

66.67

2.633.01 2.14

1.02 2.27

100

2.63

3.01 5.5 8.91

1.02

2.78

2.27 11.11

12.5

33.33

10.53

11.28 13.46 13.36

10.2

8.33

4.55 11.1112.5

100

65.79

70.68

67.28

64.37

64.29

75

65.91

55.56

62.5

0

20

40

60

80

100

16-2

0

21-2

5

26-3

0

31-3

5

36-4

0

41-4

5

46-5

0

51-5

5

56-6

0

61-6

5

66-7

0

71-7

5

Feed

ing

inte

nsity

(%)

Length class (cm)

Empty1/4 full1/2 full3/4 fullFull

N=990

79

3.2.4. Population dynamics and stock assessment

Mortality

The total mortality (Z) of C. nufar estimated by the length converted catch curve

method was found to be 1.24 (SE=0.04). The Beverton-Holt estimation provided the

Z value as 1.36 (SE=0.18) which was comparable to the value estimated by the

length converted catch curve technique. The Powell-Wetherall method gave the

mean Z/K as 3.56 (SE=0.15). The average Z calculated by both length converted

catch curve and Beverton and Holt methods which stood at 1.30.

For C. nufar, the natural mortality coefficient (M) calculated by the empirical

methods of Pauly (1980), Alagaraja (1984) and Rikhter and Efanov (1976) stood at

0.61, 0.44 and 0.80 respectively. The average of the above three values (0.62) was

close to the estimate obtained by Pauly’s techniques (M=0.61). Hence, for further

analysis, the M value was taken as 0.61. The calculated fishing mortality (F) of C.

nufar was: total mortality minus natural mortality (F = Z – M) was 0.68.

Exploitation rate (E) and Exploitation Ratio (U)

The exploitation rate (E) for the pooled data of 2005-’06 and 2006-’07 was 0.52. The

value of U estimated for the combined data of both the years was 0.38.

Yield, Standing stock, Total stock or Biomass and MSY

The catches of C. nufar for the year 2005-2006 estimated 2,075 t and for 2006-2007

2,018 t were considered as the yield of respective years. From the average annual

yield for both the years (2,047 t), the estimated annual average standing stock was

3,010 t and the annual average total stock was 5,387 t. The MSY estimated by

Cadima’s formula was 1,953 t. The Thompson and Bell analysis also showed a close

MSY of 1,946 t (Fig.66). The current yield and MSY estimates indicate that the

stock of C. nufar is marginally overfished.

80

The predicted yield and biomass decreased with the increase of F. The predicted total

biomass of 16,052 t decreased to 12,713 t at F=0.1, to 6,167 t at F= 0.5 and to 5,235 t

at F= 0.6 and at F= 2.0, the yield and biomass stood at 18 t and 57 t respectively

(Fig. 66).

Fig. 66. Predicted yield for C. nufar for different F

Yield-per-recruit and Biomass-per-recruit

In the stock of C. nufar, the yield-per-recruit (Yw/R), total biomass-per-recruit

(TB/R) and stock spawning biomass-per-recruit (SSB/R) were estimated for the F-

values ranging from 0-2 (Fig.67). It was evident that the MSY/R was 115.4 g at the F

of 1.48. However, the current estimated F was 0.68. When F was zero, the estimated

TB/R and SSB/R were 759 g and 553 g respectively (Fig. 67). These values

decreased with the increase in F. At the current F equal to 0.68, the values of Yw/R,

TB/R and SSB/R were 111 g, 260 g and 191 g respectively.

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0

500

1000

1500

2000

2500

0 1 2 3 4

Biomass (t)Yi

eld

(t)

F-factor

Yield (t)Biomass (t)

MSY

81

Fig. 67. Equilibrium yield-per-recruit and biomasses-per-recruit in C. nufar

against F (Yw/R, yield-per-recruit; SSB/R, stock spawning biomass-per-

recruit; TB/R, total biomass-per-recruit)

Optimum length of capture (Lopt)

From the empirical equation (Froese and Binohlan, 2000), the optimum length of

exploitation was calculated at 40.6 cm. The Lopt/L∞ for C. nufar was calculated at

0.58.

0

100

200

300

400

500

600

700

800

0 0.4 0.8 1.2 1.6 2 2.4

Yiel

d (g

)

Fishing mortality

YW/R (g)

SSB/R (g)

TB/R (g)

82

3.3. Distribution of C. nufar in relation to oceanography parameters

The fish C. nufar occurred throughout the survey area but more commonly in the

south to Masirah Island in waters shallower than 100 m depth (Fig. 27). Abundance

of fish was highest from January to June. During this period, the depth

range of occurrence of the species appeared greatest. There was difference in the

distribution pattern of C. nufar between the surveys done in post southwest

monsoon of 2007 and 2008. While the fish occurred in areas 1, 2 and 3 during post

southwest monsoon period of 2007 period, during southwest monsoon period of 2008

the fish occurred in areas 2,3 and 4.(Fig. 69,73). It has been noted that the

C. nufar prefer to occur at temperature between 20 and 24ºC during

NE monsoon and Spring Inter monsoon while in autumn inter

monsoon i t occur at 26–28ºC. During Post southwest monsoon 2008

the fish was found at temperature between 17ºC and 21ºC (Fig. 68).

Fig.68. Catch of C. nufar at di fferent t ime of monsoon.

0

20

40

60

80

100

120

140

15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Catc

h (k

g)

Temperature ºC

Post SW 2007

Autumn monsoon 2007

Northeast Monsoon 2008

Spring monsoon 2008

Post SW 2008

83

Fig. 69 Distribution of C. nufar: Post SW monsoon 2007

Fig. 70 Distribution of C. nufar : Autumn monsoon 2007

84

Fig. 71 Distribution of C. nufar: NE monsoon 2008

Fig. 72 Distribution of C. nufar: Spring Inter-monsoon 2008

85

Fig. 73 Distribution of C. nufar: Post SW monsoon 2008

Response C. nufar to OMZ

When the OMZs were widely prevalent, C. nufar was found closer to the coast

mainly within Masirah and Sawqirah bays during the post south west monsoon in

2007 (Sept-Oct) and post south west monsoon in 2008 (Aug-Sept) (Figs. 26,69,73 ).

By NE monsoon in 2008 (Jan-Mar), when most of the shelf waters were well

oxygenated, C. nufar was widely distributed throughout the survey area (Fig. 24, 71).

During the spring inter-monsoon period (Apr-Jun), waters were largely

deoxygenated and C. nufar were found in a narrow band nearer to shore (Fig. 25,

72). It appears that C. nufar is adapted to low oxygen level (Fig. 75). These

conditions were clearly reflected on the catch rates during different voyages. The

highest catch rate was recorded in stratum between 20 and 50 m during post SW

monsoon 2007 and 2008 while it was widely distributed during NE monsoon 2008

between 20 – 150 m depth (Fig.74).

86

Fig.74 Catch rate of C. nufar by stratum during monsoon periods

Fig.75. Occurrence of C. nufar at different level of bottom dissolved oxygen.

0200400600800

1000120014001600180020002200

Post

SW

200

7

Autu

mm

onso

on20

07

NE

mon

soon

2008 Sp

rinm

onso

on20

08

Post

SW

200

8

Kg. k

g-2

20-50 m

50 - 100 m

100 - 150 m

150 - 250 m

0

20

40

60

80

100

120

140

0 1 2 3 4 5

Catc

h(Kg

)

Dissolved O2 ml l-1

Post SW 2007

Autumn monsoon 2007

Northeast Monsoon2008Spring monsoon 2008

87

4. Discussion

Climatic variability and increasing pressure from exploitation of marine resources

and other human activities would influence and potentially modify the state and

functioning of marine ecosystems. The interaction of both climate and exploitation

are probably substantially involved in most cases for decline in fish populations and

the associated ecosystem changes as climate may cause failure in a fishery

management system, fishery exploitation may disrupt the ability of the population to

resist or adjust to climate changes

The two unique features of the Arabian Sea that significantly influence

productivity in the region are the seasonal monsoons and the occurrence of

extensive oxygen minimum zones (Wishner et al., 1998). The NE monsoon occurs

from November to mid February and the SW monsoon, with sustained strong

winds, typically occurs from June to mid September (Weller et al., 1998).

However, upwelling favorable winds along the Oman coast can begin as early as

April (Kindle and Arnone 2001).

The productivity in the region has a strong seasonal signal associated with the SW

Monsoon (Wishner et al., 1998). Filaments and jets are created by the SW

monsoon, which are capable of exporting cool, nutrient rich waters hundred of

kilometres offshore (Brink et al., 1998). Mid-open ocean upwelling occurs

offshore during the SW monsoon (Smith and Bottero1977). Features along the

Oman coast produced by the SW monsoon tend to persist into the autumn

intermonsoon period (Kindle and Arnone 2001).

The effect of the monsoon periods on water temperatures is well documented

(Wishner et al., 1998; Lee et al., 2000, Weller et al., 2002). Warm sea surface

temperatures are typically seen offshore during the SW monsoon period, with

cooler, more recently upwelled water present near-to-shore. Sea surface

temperatures are coolest after the NE monsoon (Wishner et al., 1998). CTD

88

casts during 2007–08 showed a similar pattern; nearshore temperatures were

warmest immediately before the SW monsoon, upwelling was evident immediately

after the SW monsoon, and sea surface temperatures were coolest immediately after

the NE monsoon period. T h e c ooler waters after the NE monsoon are the

result of cross-basin variations in windstress and convective overturning bringing

cool waters to the surface (Lee et al., 2000).

Cold, less saline water was noted at mid-depths, particularly to the NE of

Masirah Island and Salalah region after the NE monsoon period. Salinity

minima in midwater have been noted in other studies (Shetye et al., 1992, Weller

et al., 2002) and are thought to be the result of fresh coastal water sinking

offshore or seasonal effects of evaporation and capping of the thermocline.

Although low salinity intrusions were noted at this time, salinity in surface and

deep waters was typically high. Elevated surface salinities during and after the NE

monsoon may be the result of southward advection of highly saline surface waters

from the S e a of Oman (Warren et al., 1966) or strong evapotranspiration

association with the monsoon (Lee et al., 2000)

The OMZs is a midwater zone of low oxygen that extends from just below the

mixed layer to more than 1000 m in some areas. The core of this layer is defined as

the region where oxygen is less than 0.1 ml l-1

. .There is some debate as to how this

layer forms – large local consumption rates from high productivity in surface

waters; very slow movement within the layer, which allows decaying organic

matter to consume all oxygen present; low oxygen concentration in the waters

entering the layer from the southern ocean (Olson et al., 1993); or the lack of an

opening to seas to the north (Morrison et al., 1999).

In 2007–08, the OMZ was found at depths as shallow as 40–50 m immediately after

the SW monsoon. After the NE monsoon, waters were well oxygenated and the

OMZ was typically found at depths of 150–200 m, if observed at all. This depth

pattern was noted in several other studies (Weller et al., 1998, Wishner et al.,

89

1998), although Morrison et al. (1999) found that the OMZ had a maximum depth

of approximately 150 m. Morrison et al. (1999) found dissolved oxygen was

typically higher to the south, similar to observations described here. Naqvi et al.

(1992) found dissolved oxygen was at minimum after the NE monsoon,

increased throughout the spring inter monsoon, and reached a maximum during

the SW monsoon period. Dissolved oxygen levels less than 0.1 ml l-1 have

physiological l imi tat ions on small organisms (Morrison et al., 1999).

However , larger organisms, such as fish, are limited by slightly higher levels of

dissolved oxygen of about 0.3 ml l-1 (Ashjian et al., 2002). The present study

indicates that C. nufar can thrive even in areas where oxygen levels were low.

The distribution of C. nufar was not similar for the surveys conducted in post

southwest monsoon periods during 2007 and 2008. The f i sh occurred in areas 1,

2 and 3 during post southwest monsoon period of 2007; however, it was captured in

areas 2, 3 and 4 during post southwest monsoon period of 2008. The differences in

biomass estimates between post southwest monsoon surveys may be due to the

after-effects of the cyclone (Gonu) that hit Omani coast during June 2007 and/or

the slight difference in timing between the two surveys (the 2007 survey started 1.5

months later than in 2008).

The commercial catches of C. nufar consisted of fish with crucial lengths. The

estimated length at first capture was 31.4 cm, and the females matured at the average

length of 31.9 cm, and males matured at the average length of 33.7 cm. During July

1999 - July 2000, the catches of C. nufar from the trawl landings of Oman consisted

of about 40% of immature fish (McIlwain et al., 2006). However, in the present

study, the fish measuring up to 29 cm of TL contributed to 49% during 2005-06, 36

% during 2006-07 and 42 % for the pooled data. This clearly indicates that besides

immature individuals, sizeable portions of mature fish are also caught prior to

spawning causing recruitment overfishing. The current situation is a matter of

management concern and warrants for suggesting the legal size for capture.

90

The value of exponent b in length-weight relationship of C. nufar from South Africa

was found to be 2.7831 (Coetzee and Baird, 1981) which fell within in the range

generally found for fish (Ricker, 1971). It is interesting to note that while there was

significant difference between the slopes of the fork length-weight regressions of

males and females in an earlier study from the Arabian Sea off Oman (McIlwain et

al., 2006), in the present study, no such significant difference between the total

length-weight relationships could be established. However, the b values of males and

females in the length-weight relationships in both the studies are comparable i.e. the

males and females registered the b values of 2.872 and 2.849 respectively in the

former study, and 2.906 and 2.890 respectively in the present study.

The VBGF parameters estimated from different regions of the Indian Ocean

indicated variations in the parameter values (Table 8). However, the maximum size

of the fish in the commercial catch was reported to range between 60cm and 75 cm

(Van der Elst, 1981; Bauchot and Smith, 1984; Garratt, 1985).

Table 8. Comparison of growth parameters of C. nufar from different studies

Country L∞ (TL; cm) K y-1 t0 (y) Reference

Gulf of Aden 100 0.067 -2.96 Pauly (1978), based

on Druzhinin (1975)

Gulf of Aden 65 0.18 - Edwards et al., (1985)

Mozambique 70 0.17 - Timochin (1992)

South Africa 95.4 0.654 -2.62 Coetzee and Baird

(1981)

Oman 69.9 0.286 -0.180 Present study

91

In the present study, for the largest sized C. nufar recorded in the commercial catch

(Lmax= 64 cm), the estimated age based on length frequency would be around 11

years; however, otolith indicated an age of about 13 years (Table 6 A&B). The

Pauly’s equation (3/K) also indicated the longevity of the fish would be around 10.5

years (Pauly, 1983a). From the South African waters, based on otolith, the life span

of the fish measuring 76.3 cm was estimated to be around 22 years (Coetzee and

Baird, 1981). As per the otolith based length at age estimates provided (Coetzee and

Baird, 1981), the age of the fish measuring 64 cm in the South African waters would

be between 14 and 15 years. The difference in the age may be due to the differences

in the environmental parameters.

The growth performance index (Ø’) of C. nufar in the present study was estimated at

3.14 based on length data and 2.95 based on otolith analysis. It suggests that the

species is comparatively growing faster in the Omani waters than in Gulf of Aden

where the Ø’ was equal to 2.83 (Druzhinin, 1975) and 2.88 (Edwards et al., 1985)

and to 2.92 in Mozambique (Timochin, 1992). The sagittal otoliths in C. nufar

showed the formation of one opaque and one translucent ring each year. The high

percentage of otoliths with opaque edge was observed during July – January and

hyaline edge observed during March - June could be related to low and high values

of sea temperature respectively. The species C. nufar has a long life span in the

Arabian Sea off Oman; the maximum age estimated was 13 years for the fish 64 cm

of total length.

During the SW monsoon season due to the drop in temperature in the surface water

and higher primary productivity, few species of sparids including C. nufar spawn

along the Arabian Sea coast of Oman (McIlwain et al., 2006). However, the period

of spawning of C. nufar reported from May to August (4 months) (McIlwain et al.,

2006) was found to extend from May to October (6 months) in the present study

(Figs. 44 & 45). It is interesting to note that C. nufar spawned during winter (June -

October) along the coast of South Africa (Garratt, 1985; 1991) which may be due to

92

the optimum seawater temperature. The optimum temperature for spawning in C.

nufar lies between 18oC and 20.3oC (Garratt, 1985).

Until recently, community level spawning patterns in tropical demersal fish have

often been correlated with gross seasonal patterns in environmental condition that

might affect food supply, growth and dispersal of larvae (Robertson, 1991). One of

the main predictions of this gross environmental seasonality hypothesis is that

because the mechanisms are supposedly simple, they should affect communities in

the same way, such that the two variables, spawning and environmental conditions,

match each other (Robertson, 1991). In this study, C. nufar spawning pattern

appeared to match with one gross environmental condition, i.e. the SW monsoon,

when larval survivorship is probably maximized due to an increase in primary

productivity. During the SW monsoon, regular upwelling events occur when

seawater temperatures can decline to 16–18 ºC, but generally average to 20ºC

(Sheppard et al., 2000; Wilson et al., 2002). The pelagic productivity during the

summer upwelling months may be two orders of magnitude than that during winter

(Sheppard et al., 2000), possibly optimizing larval survival and growth. For many

species of fish, water temperature can have a pronounced effect on spawning,

particularly the rate of gonad development, with sudden increases in temperature

triggering maturation and ovulation (Bye, 1990). The exception was noticed in this

study where our results suggest that C. nufar spawned mostly during the monsoon

period when the water temperature declined to 22–25 ºC. This concurs with the

findings of Sadovy (1996), who suggested that many species of sparids spawn during

colder periods, compared with co-occurring reef fishes.

Sea water temperature can influence spawning of fish (de Vlaming, 1972; Mischke

and Morris, 1997) and in some sparids there was relationship between SST and the

timing of spawning (Dubovitsky, 1977; Buxton, 1990).

Species that could not withstand global warming-induced increase in water

temperature would be left with two alternatives, either they would shift their

geographic ranges to remain in waters of suitable temperature or the adults would

93

tolerate increased water temperatures; but, could adopt the tactics of spawning in

cooler months as in some sparids (Gucinski, et al., 1990)

Spawning and subsequent larval production often appear to be timed to match with

periods when appropriate food is likely to be abundant (Robertson et al., 1988).

Shifting of spawning season to cooler months in tropical species would possibly

reduce the duration of spawning and hence, there could be far reaching consequences

in the structure of fish faunas and fisheries. The change in timing of spawning and

subsequent recruitment in reefs or estuaries depended on seasonal hydrographic

patterns for larval supply would harm recruitment of desired species and may lead to

recruitment of different species (Gucinski, et al., 1990). Further, the eggs and larvae

depending on seasonal hydrographic patterns for transport to nursery and feeding

grounds could be transported to inappropriate areas (Norcross and Shaw, 1984).

Such alterations in recruitment patterns will lead to major species shifts in fish

community structure and biodiversity in an area.

Depending on the spawning habits of teleostean fishes (Hickling and Ruternberg,

1936; James, 1967), C. nufar falls under the group III fishes that spawn more than

once a year similar to several other fish species in the Indian Ocean region (Prabhu,

1956; Jayabalan, 1986; Reuben et al., 1992). Estimating size at sexual maturation in

relation to capture size is essential to minimize the catch of immature individuals and

to determine the size at which individuals enter the reproductive population

(Sadovy,1996). In the present study, females matured at an earlier length than males

as observed earlier (McIlwain et al., 2006). In some demersal fish species of Oman,

female attains maturity earlier than male (McIlwain et al., 2006). In the South

African waters, 50% of maturity in female C. nufar was obtained at 25 cm FL

(Garratt, 1985) which was lower than the observed Lm in female in the present study

(31.9 cm TL or 28.3 cm FL) and in the earlier study (29.2 cm FL) from Oman

(McIlwain et al., 2006). While, the male to female ratios of C. nufar tested by chi-

square test did not differ significantly in the Omani waters (McIlwain et al., 2006) as

observed in the present study, in South Africa, the male to female ratio was found to

be 1: 2.5 (Garratt, 1985a) and 1: 2.0 (Buxton and Garratt, 1990). Sex change, where

94

individuals function as both sexes either sequentially or simultaneously, is a common

reproductive strategy in tropical reef fishes, occurring in nearly 50% of families

(Hourigan and Kelly, 1985; Sadovy,1996). Protogyny and protandry have been

found in 10 families and the family sparidae is one of them. Establishing whether a

species undergoes sex change is critical to fisheries management. Protogynous

species, for example, are particularly vulnerable to overfishing as gear selectivity

reduces the reproductive capacity of these species by removing the female fish in the

older year classes, thereby decreasing the probability that eggs are successfully

fertilized (Huntsman and Schaaf, 1994; Sadovy,1996). Determining the mode of

reproduction for a hermaphroditic species is essential as managing such a fishery can

be considerably complicated if there is a bias in the sex-ratio that goes undetected

(Ferreira, 1993). To establish sexual functionality for C. nufar definitive

classification must come from a study of gonadal histology or through experimental

manipulation (Sadovy and Shapiro, 1987). If the former is to be performed, it should

involve a large sample size that is representative of all size classes and taken

monthly from one location (Sadovy and Shapiro, 1987).

In the present study, the fecundity of C. nufar generally increased with the size, body

weight and ovary weight of fish and the minimum and maximum fecundity ranged

from 11,406 to 473,277 eggs in fish measuring 29 cm and 63.4 cm respectively

(Annex 2). However, slightly higher values of fecundity that ranged from 13,050 to

560,566 eggs were reported in the fish of the sizes 21.1 cm to 62 cm from the South

African waters (Garratt, 1985).

The food analyses of the gut clearly indicated the fish as the most preferred food of

C. nufar that also on cephalopods, crustaceans and polychaete worms (Figs. 58, 59).

While, the crustaceans were preferred in minor quantities by size groups of 16-30

cm, cephalopods and polychaetes were preferred by small and medium sized fish.

Feeding on nektonic and benthic forms by C. nufar especially on fish as primary

food item and occasional feeding on cephalopods crustaceans and polychaetes has

been observed from the Gulf of Aden (Druzhinin, 1975) and South African waters

(Coetzee and Baird, 1981; Smale, 1986).

95

Occurrence of empty stomachs in several species of fishes from the Arabian Sea is

common (Sreenivasan, 1974; Naik et al., 1990; Kalita and Jayabalan, 2000). About

54.9% of C. nufar occurred with empty stomachs from South Africa (Coetzee and

Baird, 1981). However, in the present study from Oman, the empty stomachs in C.

nufar accounted for about 67.5% (Figs.63, 64, 65). Though, the spent fish feed

actively (James, 1967; Jayabalan and Ramamoorthi, 1985; Jayabalan, 1988) to

balance the lost energy during spawning, active, moderate and poor feeding in C.

nufar occurred in all the maturity stages of males and females indicating

inconsistency in feeding intensity (Fig. 64). The incidence of empty stomachs in fish

may be related to the regurgitation (Job, 1940); high calorific value of the diet

consumed (Longhurst, 1957; Sreenivasan, 1974) and faster rate of digestion (Qasim,

1972).

No information is available on the mortality parameters of C. nufar from previous

studies. In the present study, the total mortality (Z), natural mortality (M) and

fishing mortality (F) were estimated at 1.3, 0.62 and 0.68 respectively. The Z/K was

found to be 3.56 (SE=0.15). In fishes, the growth coefficient K is closely related to

natural mortality and high K indicates high natural mortality (Vivekanandan, 2005).

The M/K ratio is almost constant among closely related species and similar

taxonomic groups (Beverton and Holt, 1959; Banerji, 1973) that varies from 1 to 2.5

(Beverton and Holt, 1959). In the present study, the M/K ratio estimated for C. nufar

was 2.13.

The optimum exploitation rate (E) is assumed to be close to close to 0.5 and the

sustainable yield is optimized when F≈M (Gulland, 1971). In the present study, the

estimated E was equal to 0.52 which is marginally higher than the optimal rate of

exploitation. As the MSY estimated by the Cadima’s estimator (1,953 t) and

Thomson and Bell technique (1,946 t) was slightly higher than the yield (2,047 t)

obtained during the period of study. The current yield and MSY estimates indicate

that the stock of C. nufar is marginally overfished. To harvest the fish at the

estimated MSY level, a reduction of 17% of effort from the present level (F= 1) is

96

needed. The MSY per recruit estimated as 115.4 g at 1.48 F appears not realistic as at

the current F = 0.68, the stock is subjected to overexploitation.

The effects of fishing of larger individuals, besides, having substantial direct

consequence on the population, can influence the capacity of population to withstand

climate variability through other pathways such as effects on migration and parental

care. Hence, in an ecosystem, elimination of species that might occur due to fishing

may be destabilizing with reduced resilience to perturbations. Indiscriminate

exploitation of marine resources might promote increased turnover rates in marine

ecosystems, which would worsen the effects of environmental changes. Overall

reduction in marine diversity at the individual, population and ecosystem levels

would lead to a reduction in the resilience and an increase in the response of

populations and ecosystems to future climate variability and change. Hence, future

management plans need to consider the structure and functioning of populations and

ecosystems in a broader sense to help maximise the ability of marine fauna to adapt

to future climates.

97

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110

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111

Annex 1B. Developmental stages of C. nufar ovary based on histological examination

Immature

Ovary is small, tightly packed and dominated by

previtelogenic, primary growth stage oocytes. The

gonad wall is thin with no evidence of prior

spawning in the form of post ovulatory follicles,

atretic cortical alveolus (yolk vesicle) or

vitelogenic (yolk gobule and migratory nucleolus

stage) oocytes, brown bodies or scaring (stromal

tissue) in the gonad

Maturing, Mature

Yolk vesicle stage is the most advanced oocyte

present. The ovary is dominated by

previtellogenic, primary growth ooctyes

(chromatin nucleolar and perinucleolar stages)

RipeOvary is in active vitellogenesis. Oocytes in all

stages of development are present: yolk vesicle,

yolk globule and mingrstory stages oocytes

dominate. Yolk globule or migratory-nucleolus

stages are the most advanced oocyte(s) present.

112

Annex.2. Fecundity in C. nufar

S. No. Total length (cm) Total wt (g) Gonad wt. (g) Fecundity

1 28 280 9.79 30,574

2 28.8 310 3.77 12,897

3 29 312 3.5 11,406

4 30.6 382 4.72 14,759

5 31.7 420 4.22 12,592

6 32.2 420 5.91 13,132

7 32.6 448 9.19 27,202

8 32.7 470 7.32 18,922

9 34 486 8.17 23,423

10 34.5 516 5.99 17,718

11 34.5 546 11.42 32,843

12 35 552 10.29 31,919

13 36.2 692 12.16 36,188

14 36.3 636 6.94 20,105

15 38 680 10.51 35,996

16 38.3 800 25.65 77,232

17 38.8 546 10.19 31,772

18 43.7 1032 21 65,583

19 47 1314 30.45 79,809

20 47.2 1326 53.91 168,522

21 50.2 1788 63.69 204,699

22 51.6 1986 63.05 200,940

23 51.8 1805 39.71 109,281

24 52.5 2063 46.82 139,008

25 56.4 2414 77.91 195,632

26 61.5 3178 103.08 326,248

27 63.4 3730 185.91 473,277