Stock Assessment of the Queen Conch Population of Belize

STOCK ASSESSMENT OF THE QUEEN CONCH (Strombus gigas) POPULATION OF

BELIZE

By:

Ramon Carcamo Jr.

Belize Fisheries Department Ministry of Agriculture and Fisheries

2006

________________________________________________________________________ Conch Stock Assessment 2006

2

ABSTRACT The Queen Conch, Strombus gigas, is one of the six species of the family Strombidae in the Western Atlantic region. Its geographic distribution extends from Florida throughout the Caribbean and into the northern coast of South America to Brazil. This Gastropod species has been Belize’s second largest marine export commodity for the past three decades. The exploitation of this species has contributed significantly to the well being of fishermen and the country’s economy. During the last decade the annual production of Queen Conch has ranged between 181.6t and 272.5t, which was exported to the United States of America. In 1992 the Convention on International Trade in Endangered Species of Wild Fauna and Flora’s (CITES) placed the Queen Conch in Appendix II. Underwater visual surveys were conducted from Northern part of Bacalar Chico and along the barrier reef complex up to Sapodilla Cayes. Divers were responsible to count and take some morphometric data from each conch found within the transect area. Microsoft Excel program and SPSS statistical package was used to run descriptive statistics. Legal size conch abundance was estimated to be approximately 9,508,049(95% C.I., 6,355,871--12,660,224) individuals, which translated into 3,565,518 lbs (95% C.I., 2,383,452--4,747,584) of conch. Schaefer Model resulted in MSY to be 1,086,815 lbs (95% C.I., 811,371—1,369,515). Fox Model resulted in MSY to be 935,446 lbs (95% C.I., 745,741—1,140,173). Key Words: Maximum Sustainable Yield, Stock assessment, CITES


3

INTRODUCTION The Queen Conch, Strombus gigas, Linnaeus, 1758, is a large marine gastropod mollusc

of the order Mesogastropoda. It is one of the six species of the family Strombidae in the

Western Atlantic region. Its geographic distribution extends from Florida throughout the

Caribbean and into the northern coast of South America to Brazil (Chakalall and

Cochrane, 1996; Wood, 1995; Tewfik, 1996). The Queen Conch has been one of the most

important fishery resources in the Caribbean region. Prior to the commercial exploitation,

the Queen Conch had been fished for subsistence and is still classified as an artisanal

fishery in Belize.

This Gastropod species has been Belize’s second largest marine export commodity for

the past three decades. The exploitation of this species has contributed significantly to the

well being of fishermen and the country’s economy. During the last decade the annual

production of Queen Conch has ranged between 181.6t and 272.5t, which was exported

to the United States of America. The United States imports approximately 80% of the

world’s trade, usually resulting in imports of more than 1,000 metric tons of conch meat a

year (NOAA, 2003).

In 1992 the Convention on International Trade in Endangered Species of Wild Fauna and

Flora’s (CITES) placed the Queen Conch in Appendix II. Appendix II lists species are

species that are not threaten presently with extinction, but may become so unless trade of

such species is subject to strict regulation to avoid utilization incompatible with their

survival. Trade in Appendix II listed species is allowed only under a permit and only if

such export will not threaten the survival of that species. In 2003 CITES placed embargo


4

on three conch exporting countries (Honduras, Haiti and the Dominican Republic) during

that same period CITES also gave an outline recommendations to several countries as

how to proceed in order to continue to export conch. Therefore, Belize was given a short

and long term actions to be taken, only to list a few were to establish a catch quota,

establish conversion standards and assess the conch population.

In 1996 a national conch survey was conducted. From the1996 survey it was determined

that the population of legal size conch in Belize was 2,259,000 (95% C.I. =1,570,000 -

3,760,000) at a mean weigh of 170 grams (6 oz) per individual. The Maximum

Sustainable Yield (MSY) was estimated to be approximately 190,000kg (420,000 lbs). It

was recommended that a conservative management approach be applied and that further

studies be undertaken. It was also determined that the population was dominated by

juveniles (approximately 70%) greater than 10 cm in length and that adults made up 20

percent of the population. The interpretation then could be that the population of Queen

Conch in Belize is overexploited and running the risk of stock collapse due to poor

spawning rates (Appeldoorn 1996).

In 2003 the Belize Fisheries Department conducted a national assessment of the Queen

Conch population in Belize. One of the conclusions was that the population of conch in

Belize had increased by three fold as compared to the results from the 1996 population

assessment. This increase in abundance was significant in the Northern and Central

fishing zones of Belize. It was also concluded that the no-take areas and deep water areas

consisted higher densities of conchs as compared to shallow fished areas. Another

important result of the assessment was that it was demonstrated how the marine reserves


5

were effective management tools, because it was determine how marine reserves

consisted of higher abundance of adult conchs as compare to fished areas. The Maximum

Sustainable Yield was calculated to be 712,601.1 lbs (range: 633,278 – 959,241 lbs)

(Appeldoorn, 2003).

Also in 2004 the Fisheries Department conducted another national assessment of the

conch population in Belize. It was estimated the legal conch densities were significantly

higher in no-take zones in the marine reserves. Furthermore, adults were on average,

larger in deep areas, indicating that adult populations arise primarily from direct larval

settlement and not from migration from shallow areas. So, it was found the marine

reserves contained a high proportion of very small adults of conchs (Appeldoorn, 2004).

The objective of the project was to conduct a stock assessment of the Queen Conch

population of Belize and estimate the Potential Yield of the resource.

MATERIALS AND METHODS Study area:


6

The Belize Barrier Reef Complex has been

classified as the second largest continuous reef

system in the Western Atlantic region

(Arrivillaga, 2004). The Belize Barrier Reef

exhibits the classic Barrier reef stratification

pattern as described by Rutzler and Macintyre

(1982). The reef complex includes an

emergent reef crest (within 20 cm of sea level)

along 57% of the total 257 km outer

continental shelf platform (Burke, 1982). The

reef complex has been described to have three

provinces, which the Northern Province

contains approximately 46 km of shallow-water from Rocky Point to Gallows Point. The

central province contains approximately 91 km of shallow- water reefs from Gallows

Point to Gladden Spit. While the southern province contains only 10 km of shallow-water

of barrier reef from Gladden Spit to the Sapodilla Cayes (Macintyre and Aronson, 1997).

Also Glover’s Reef and Lighthouse Reef Atoll have deep, well- circulated lagoons with

patch reefs. While Turneffe Atoll has shallow poorly circulated lagoon and fewer patch

reefs (Stoddart, 1962).


7

Traditional conch fishing grounds are normally situated at the shallow (5-15 ft) back reef

waters usually populated with sea grass, sand and algae. Conch habitat distribution has

been observed to be found from the northern back reef of Bacalar Chico Marine Reserve,

which parallels the Barrier Reef complex and is directed due south including sea grass

beds and patch reefs. Conch habitat distribution continues down towards the Sapodilla

Cayes Marine Reserve, furthermore at the three atolls conch habitat is normally observed

to be along the inner periphery of the atolls.

Sampling:

The method used to quantify abundance was to conduct underwater visual surveys

whereby a belt transect was placed perpendicular from the coral reef crest, while being at

the back reef and aligned due west towards mainland. Each belt transect was 500 meters

long, which was made from nylon rope and a 2 lbs lead weight was attached at each end.

Two divers would dive along the transect line while being 2 meters apart on either side of

the transect line. The surveys geographic position was recorded using a Garmin hand-

held Global Positioning System (GPS). The zones surveyed were Bacalar Chico Marine

Reserve, Caye Caulker Marine Reserve, Hol Chan Marine Reserve, Caye

Chapel/Gallow’s Point, South Water Marine Reserve, English Caye/Tobacco range, Port

Honduras Marine Reserve, Laughing Bird/Gladden Spit, Sapodilla Marine Reserve,

Lighthouse Reef atoll, Glover’s Reef atoll and Turneffe atoll. Each diver was responsible

to count and take some morphometric data from each conch found within the transect

area. Shell length (LTH) (tip of the spire to the siphonal canal) was measured to the

nearest millimeter using a measuring board. The shell lip thickness (LIP) (mid-lateral

region on the lip side of the shell approximately 40 mm in from the edge of the shell) was

measured to the nearest 0.1 mm also using sliding vernier calipers. Other data such as

depth, habitat description and other observation were also recorded. Furthermore,

samples of adult conchs were taken from each zone and other morphometric data were

gathered such as Total weight (g), Total length (mm), market clean weight (g) and fillet

weight (g).

Data analysis:

The data collected from each zone was reviewed and digitized in a Microsoft Excel

spreadsheet. Microsoft Excel program and SPSS statistical package was used to run

descriptive statistics. Also Global Information System (GIS) technology was in

ArcGIS(9.0) and a theme with shape-file layers of coral reef, marine habitat, marine

protected areas demarcation and Lansat of Belize to geographically plot the transects

(Annex 1). In addition it was used to estimate potential conch habitat areas along the

Barrier Reef complex (Annex 2). The length frequency data was sorted by size/age

classes as describe by Appledoorn (2003). The density of legal adult conch for each

transect was estimated as Density = ∑ x/a, where [x = number of individuals; a =

sampling unit area] and Mean density = [(∑ x/a) 1 + (∑ x/a)2+ …. + (∑ x/a)n]/n.

Furthermore, total abundance of legal adult conch was estimated as N = [(∑ x/a)1 + (∑

x/a)2+ ….+(∑ x/a)n]/n* A, where A = total conch habitat area. Potential yield was

estimated based on the Surplus Production models where the Schaefer and Fox models

were applied to estimate Maximum Sustainable Yield (MSY).

>1-(Y/MB)< MB= MSY(Y/B)-2M

BM = F-2M

BM = MSY

F

2 2

S

exp

Potential Yield =

Assumption M = 0.5 and Y = 633,070 lbs.


8

RESULTS


9

Shell length – Lip thickness Relationship:

kness Regression relationship

The Shell lengt oor correlation

Shell Length-Lip thickness Relationshipn =142

y = 0.0328x + 12.82R2 = 0.0525

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350

Shell Length(mm)

Lip

thic

knes

s(m

m)

Fig.1 Shell length-Lip thic

h- Lip thickness relationship resulted as having a p

coefficient and was expressed as y = 0.0328x + 12.82 (R2 = 0.0525). It was observed that

5.2% of the variation in shell length was due to variation in lip thickness (Figure 1).


10

otal Weight- Total Length Relationship:

Fig. 2 Total weight-Total length regression relationship

The lnTotal We oor correlation

Linear Regression

Regression (n = 146)

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6.50

7.00

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8.00

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lntw = 5.76 + 0.45 * lntlR-Square = 0.13

1.00 1.50 2.00 2.50 3.00

lntl

ight - lnTotal length relationship resulted as having a p

coefficient and was expressed as lnTotal weight = 5.76 + 0.45*lnTotal length (R2 = 0.13)

It was observed that 1.3% of the variation in Total weight was due to variation in Total

length (Figure 2).


11

arket clean- Total length relationship:

The ln Market clean - lnTotal length relationship resulted as having a poor cor

oefficient and was expressed as lnMarket clean = 3.29 + 0.47*lnTotal length (R2 = 0.11)

It was observed that 1.1% of the variation in Market clean weight was due to variation in

Total length (Figure 3).

Linear Regression

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4.00

4.50

5.00

5.50ln

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lnmclean = 3.29 + 0.47 * lnlength

R-Squar e = 0.11 1.00 1.50 2.00 2.50 3.00

lnlength

Fig. 3 Market clean- Total length regression relationship

relation

c


12

ender structure:

TABLE 1. The ratio between male and female conch

he prese

approximates a male to female ratio of 1:1 (Table 1 and Figure 5).

G

Fig. 4 F

SEX

SEX

MF

Perc

ent

60

50

40

30

20

10

0

ig. 5 SEX T nce of Male and female conchs were observed, which the male was identified

as having a verge and the females as having an egg groove (Figure 4). A total of 145

adult conch were scarified which resulted in 52.4% in males and 47.6% as females this

69 47.6 47.6 47.676 52.4 52.4 100.0

145 100.0 100.0

FMTotal

ValidFrequency Percent Valid Percent

CumulativePercent


13

The mean lip thickness of adult conchs was estimated as 4.8 mm (s.d. = 4.39; n =

145). Younger adults appear to be more abundant in shallow back reef areas (Fig. 6).

Lip thickness frequency distribution:

LP

25.022.5

20.017.5

15.012.5

10.07.5

5.02.5

0.0

LP

Freq

uenc

y

60

40

30

20

10

0

Std. Dev = 4.39 Mean = 4.8

N = 145.00

50

Fig 6. Shell lip thickness frequency distribution


14

otal length frequency distribution:

Fig. 7 Total shell length distribution A total of 5,545 conchs were observed in 153 transects, which resulted in 54% to be

considered sub-legal size .8 cm. Furthermore, 46%

T

LENGTH FREQUENCY OF QUEEN CONCHn = 5,545

-200

0

200

400

600

800

1000

15 30 45 60 75 90 105 120 135 150 165 180 195 210 225 240 255 270 285 300

LENGTH(mm)

or having a total length less than 17

were considered as legal size conchs, which were greater than 17.8 cm total length. A

histogram distribution plot resulted in the identification of three possible cohorts in the

present population (Figure 7).

FREQ

UEN

CY

2006

1+

2+ 3+

-legal=54% al = 46%

SubLeg

MEAN LENGTH OF CONCH FOUND AT THE 12 SITES

0

20

40

60

80

100

120

140

160

180

200

220

240

SouthWaterCaye MPA

Hol_Chan MPA

Sapodilla Cayes MPA

Turneffe Atoll

English Caye/Tobacco

Glover's Reef Atoll

Port Honduras MPA

Caye_Caulker MPA

LightHouse Reef_Atoll

Laughing_Bird/Gladden Spit

Bacalar_Chico MPA

Caye_Chapel/GallowsPt

SITE

MEA

N L

ENG

TH(m

m)

Mean Length

Fig. 9 Mean shell length of conchs found at the 12 sites surveyed

The mean shell length of conchs found at each site was estimated, which resulted in that


15

South Wate e Reserve,

r Caye Marine Reserve, HolChan Marine Reserve, Sapodilla Marin

Turneffe Atoll, English Caye/Tobacco Range, Glover’s Reef Atoll and Port Honduras

Marine Reserve to be 143.6 mm,144.8, 155.3 mm, 158 mm, 163.4 mm, 172.6 and 175.3

mm respectively. While, Caye Caulker Marine Reserve resulted with a mean length of

178.3 mm (7 inches), also it was estimated Lighthouse Reef atoll had a mean length of

179.9 mm. In addition at Laughing Bird/Gladden Spit the mean length was estimated to

be 189.8 mm, and then at Bacalar Chico Marine reserve the mean length was 198.7 mm.

Furthermore, Caye Chapel/Gallows Point mean length was 213.5 mm (Figure 9).

Observed abundance:

OBSERVED CONCH FROM 153 TRANSECTS

-

500

1,000

1,500

2,000

2,500

CONCH

FREQ

UEN

CY

Series1 1 567 1,096 961 800 2,085 1,073 1,873

J_1 J_2 J_3 J_4 Legal Size Conch w/ Lip"adult"

ADULT > 17.8 cm TotLegconch

Fig. 8 Observed conch numbers from the 153 transects Only one (1) juvenile conch that was less than 5 cm total length (TL) was recorded, while

567 juveniles that ranged from 5 – 10 cm (TL) were found. Furthermore, 1,096 juveniles


16

en 10 -15 cm (TL) were observed. Also it was observed that larger

veniles classified to range from 15-17.8 cm (TL) were recorded to amount to 961

individuals. However, during the survey it was observed that approximately 800 juvenile

conchs were found, which were considered legal to be fished. Nevertheless, it was also

observed that 2,085 adult conch with “flared shell lip” were encountered during the

survey. Though, of this value only 51.4% adult conchs could be considered legal to be

harvest. Therefore, it was estimated that approximately 1,873 legal size conch were

encountered during the entire survey (Figure 8).

with total length betwe

ju

ESTIMATED JUVENILE ABUNDANCE:

ABUNDANCE OF JUVENILE CONCH (J_1--J_4)

-

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

JUVENILE

AB

UN

DA

NC

E(N

o/he

ctar

es)

Abundance 3,509 2,436,927 5,220,291 4,788,822

J_1 J_2 J_3 J_4

Fig. 9 Estimated abundance of Juveniles conchs

The abundance of juvenile conchs in the different size ranges was estimated, which

resulted in J_1 (>5 cm) to be approximately 3,509 individuals. Furthermore, J_2 (10-15


17

cm) was estimated t was estimated that o amount to 2,436,927 individuals. In addition it

5,220,291 individuals of J_3 presently exists in the stock. Plus, J_4 conchs were

estimated to amount to 4,788,822 individuals (Figure 9).


18

ENSITY DISTRIBUTION:

Fig. 10 Distribution of densities of adult conch at the sites

ensity was estimated for each site surveyed, which resulted in Hol Chan Marine

eserve to have the highest density with 483 conchs per hectare. This was second by

Northern Turne hs per hectare.

D

D

R

ffe atoll and was estimated to have a density of 183 conc

The other area of interest was known to be between Laughing Bird Caye and Gladden

Spit, and the estimated density was 156 conchs per hectare. Also Lighthouse Reef Atoll

resulted with 103 conchs per hectare. The density of Bacalar Chico, Caye Caulker Marine

Reserve, Caye Chapel/Gallows’ Point, South Water Caye Marine Reserve, Port Honduras

Marine Reserve, English Caye/Tobacco range, Glover’s Reef Atoll, and Sapodilla Caye

Marine Reserve resulted with 72.66,72.78, 18.44, 53.33, 31.11, 81.4,72.1 and 17.63

conchs per hectare respectively.

DENSITIES OF ADULT QUEEN CONCHn = 12 sites

-

100.00

200.00

300.00

400.00

500.00

SAMPLING SITES

DEN

SITY

600.00

No/

hact

ares

)(

Density(No./ha) 72.66 72.78 18.44 483.00 53.33 31.11 81.40 103.46 72.10 156.36 17.36 183.33

Bacalar Chico Caye CaulkerCaye

Chape/Gallow's Pt

Hol Chan MPA SWCMR

PortHonduras MPA

EnglishCaye/Tobaco

Half Moon Caye

Glover's Reef atoll

Laughing Bird/Gladden

spit

Sapodilla Cayes

Turneffe Atoll

SHALLOW WATER CONCH DENSITY

200

250

0

25

50

75

100

125

150

175

225

SITE

DE

NSI

TY

(NO

./hec

tare

s)

1996 6.64 2.97 15.03 14.3

2003 27.54 0 0 38.89

2004 214.34 0 0 43.95

2006 183.33 103 72.09 109.6

Turneffe Atoll LightHouse Atoll Glovers Reef Barrier Reef


19

conch along the Barrier r onchs/hectare. While, in

Fig. 11 Shallow water conch density

It was observed that conch densities have generally increased from three atolls (Turneffe,

Glover’s Reef and Lighthouse Reef atolls). In addition it was observed that the density of

eef in 1996 was estimated at 14.3 c

2003 the density increased to 38.89 conchs/hectare. Furthermore, it continued to increase

in 2004 to 43.95 conchs/hectare. However, in 2006 it was further observed that conch

density increased to 109.6 conchs/hectares (Figure 11). The density of conch found along

the barrier reef in 1996 increased by seven (7) fold in 2006(Figure 11).


20

OTENTIAL YIELD:

he estimated population of legal-sized conch in Belize was 9,508,049 (95% C.I. =

,355,871 – 12,660,224) individuals. At a mean value of 170 g (6 oz) per individual, the

itable biomass was approximately 1,620,690 kg (3,565,518 lb).

P

T

6

estimated average explo

Therefore, the Maximum Sustainable Yield (MSY) using the Schaefer Model resulted in

492,643 kg (1,083,815 lbs) (95% C.I. = 811,371 lbs – 1,369,515 lbs). The Maximum

Economic Yield (MEY) was estimated to be 722, 543 lbs. While, the Fox model resulted

with an MSY of 425,202 kg (935,446 lbs) (95% C.I. = 745,741 lbs – 1,140,173 lbs). The

MEY was estimated to be 623,631 lbs.


21

ISCUSSION

o significant correlation was established between total length and lip thickness. Possibly

is because, conch grows in length in a spiral pattern in the juvenile stage, getting longer

at maturation they put out the flared lip. So, further shell growth occurs

D

N

it

as they age; but

only as thickening of the shell lip (Appeldoorn, 1997). Linear regression between market

clean meat and total length resulted in a weak correlation. Also applying linear regression

between total weight and total length resulted in a weak correlation. Possibly contributing

to the concept that meat weight increases clearly during juvenile growth. So, within about

a year of maturation meat weight ceases to increase. It is suspected that meat weight

declines in very old conch, as the decreased volume within the shell can no longer

accommodate a large amount of tissue. This type of growth pattern has been described as

deterministic growth (Appeldoorn, 1997). The spatial variations in growth and

morphology of conch have been also correlated to environmental habitat conditions

(Alcolado, 1976). So, the application of size limits to conch is not so simple and can

greatly affect the distribution of fishing effort in the different zones. On the other hand,

one of the oldest management measures taken in fisheries management is the application

of size limits or minimum size. The reason is to prevent the capture of fish considered

small, therefore allowing the fish to spawn at least once. This is to assist in maximizing

yield or maintaining spawning stock. Presently there is a size limit of 7 inches (17.8 cm)

conch shell length in Belize. The application of the concept to this species could be

adopted, because the common fishing method is by free diving and conchs is taken by

hand. This allows the fishers to be selective in capturing the conchs and also the

probabilities of surviving are greater when sub-legal conchs are returned in water.


22

conch

ed when conch are

high densities. It was found mating does not occur with conch densities below 56

Nevertheless, the implementation of minimum size limit would cause spatial

heterogeneity in the capture of conch. Due to the deterministic growth behavior, conch

that matures at a size smaller than the legal size will never be legal to capture; also

that mature at a greater size than the legal size will be captured as juveniles (Appeldoorn,

1997). Caye Caulker Marine Reserve resulted with a mean length of 178.3 mm (7

inches), also it was estimated Lighthouse Reef Atoll had a mean length of 179.9 mm. In

addition at Laughing Bird/Gladden Spit site the mean length was estimated to be 189.8

mm, and then at Bacalar Chico Marine reserve the mean length was 198.7 mm.

Furthermore, Caye Chapel/Gallows Point site mean length was 213.5 mm. However, the

mean shell lengths at the other sites were considered below legal size.

The ratio between male and female conch was approximately 1:1; possible an indication

of the stock having good probabilities of reproducing and it is accelerat

in

ind/ha and spawning failed where densities were below 48 ind/ha, which attributed to the

“Allee effect”, where negative rates of per capita population growth occur below critical

population levels (Stoner and Ray-Culp, 2000). The densities at Bacalar Chico Marine

Reserve, Caye Caulker Marine Reserve, Hol Chan Marine Reserve, English

Caye/Tobacco range, Lighthouse Reef Atoll, Glover’s Reef Atoll, Laughing

Bird/Gladden Spit and Turneffe Atoll were greater than 56 ind/ha, possibly indicating

mating and spawning has been taking place there. However, densities were below 48

ind/ha at Caye Chapel/Gallos’ Point, Port Honduras Marine Reserve and Sapodilla Cayes

Marine Reserve. Therefore, there would be little probabilities mating and spawning has


23

5mm). Further length

equency analysis of total shell length resulted in the identification of 3 possible cohorts

.I.,

,383,452--4,747,584) of conch. Schaefer Model resulted in MSY to be 1,086,815 lbs

been taking place there. Estimates of densities resulted that Hol Chan MPA had the

highest density, which was followed by Turneffe atoll and an area from Laughing Bird to

Gladden Spit. Also it was observed that the density along the Barrier Reef complex

increased significantly as compared from density recorded in 1996.

Mean Lip thickness was estimated as 4.8 mm suggesting that the conch population is

comprised of sub-adult; but also getting close to adulthood (Adult~

fr

as described by Alcolado, 1976; Berg, 1976; Brownell, 1977; Appeldoorn, 1990.

Therefore, there could be two possible cohorts of approximately 9.9 million individuals

that would be entering the fishery within the next 3 years to replenish the adult stock.

Legal size conch abundance was estimated to be approximately 9,508,049(95% C.I.,

6,355,871--12,660,224) individuals, which translated into 3,565,518 lbs (95% C

2

(95% C.I., 811,371—1,369,515). Fox Model resulted in MSY to be 935,446 lbs (95%

C.I., 745,741—1,140,173). The present MSY is more than the one estimated in 1996 and

2003 and carefully consideration must be expressed in the interpretation of these

reference points as guide when making decision to accomplish the harvesting goals of the

fishery. It must be recognized that application of the Surplus Production was guided with

assumptions and many uncertainties; therefore a precautionary approach is emphasized

when using the MSY values. It is recommended that MSY should be used as limits rather

than target points and should be reviewed every 2 years. It is also important to create a


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ed to use the lip thickness of 5 mm as the legal size to exploit conch

Belize. This would ensure that only adult conchs are harvested, while the juvenile

buffer or a precautionary reference point to reduce the probabilities of over-fishing of the

stock. Therefore, the implementation of a catch quota or Total Allowable Catch (TAC) as

an intergraded management measure to control exploitation and optimize economic

performance is strongly recommended. Furthermore, an emphasis on the precautionary

approach is also recommended that the quota should be set at 75% of the estimated MSY

according to the uncertainties of the assessment. On the other hand, it is also

recommended that an economic assessment of the fishery should follow the introduction

of the quota management system to determine the impacts on the individual operator’s

financial situation.

Another recommendation is that the present size limit of the conch should be reviewed

and should be adjust

in

stock would remain protected contributing to the sustainability of the stock. Nonetheless,

the present management tools such as marine protected areas, temporal and spatial

closure should remain and used jointly as it has proved in previous assessment to have

contributed significantly in the stock management.


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CKNOWLDEGMENTS:

hanks are extended to the management of each marine reserve who contributed and

athered the necessary data. The collaborators of each marine reserve are as follows:

o, Shane Pech, Jason Edwards, Dwayne Garcia, Hector

A

T

g

Kirah Forman, Edgar Badill

Cunningham, Elvis Williams, Nidia Ramirez, Hampton Gamboa, Joel Cho, Alicia Eck,

Godwin Humes, Jason Guy, Sherwin Perera, Miguel Alamilla, and Grimaldo Acosta. A

special thanks is extended to members from the Capture Fisheries Unit, who are as

follows: Jaime Villanueva, Kenneth Esquivel, Marsha Vargas and Mauro Gongora. The

Capture Fisheries Unit was the major executing arm of the project and without their

contribution the project could not have been a success.


26

EFERENCES:

Alcolado, P.M.1976. Growth, morphological variations of the shell and some biological data of the conch Strombus gigas. L.( Mollusca, Mesogastropoda).

1990). Growth of juveniles Queen Conch Strombus gigas Linnaeus

1758 off La Parguera, Puerto Rico. Shellfish Res.

BELIZE.

ch Strom ze.

DA A Arrivillaga, A. and M. Angel Garcia. 2004.Status of Coral Reefs of the Meso-American

the practicality of its mariculture. Mar. Biol.

gilis in los Roques, Venezuela. Bull.Mar. Sci.

n- gement. In. Posad JM and Garcia-

Moliner(eds): Proceedings of the First International Queen conch Conference, San

arcia, S., P. Sparre and J. Csirke. (1980) Estimating Surplus Production and Maximum

x at Carrie Bow Caye, Belize. Pg. 9-45 in Rutzlerk and

Macintyre I.M.(Eds) The Atlantic Barrier Reef Ecosystem at Carrie Bow Caye,

toddart.1962. Three Caribbean Atolls: Turneffe Islands, Lighthouse Reef, and Glover’s Reef, British Honduras. Atoll Res. Bull.87

R

Appeldoorn, R.S. (

Appeldoorn1 R. and Wolfgang Rolke2 . 1996. STOCK ABUNDANCE AND

POTENTIAL YIELD OF THE QUEEN CONCH RESOURCE IN

Appledoorn R.2003. Report of the analysis of data collected during the queen con( bus gigas) visual surveys of November 2003 in Beli Appledoorn R. 2004. ANALYSIS OF THE 2004 BELIZE CONCH SURVEY T

Barrier Reef System Project Region, and Reefs of El Salvador, Nicaragua and the Pacific Coasts of Meso-America. Berg, C.J. Jr. (1976). Growth of the Queen Conch Strombus gigas with a discussion of Brownell, W.N.(1977). Reproduction, laboratory culture and growth of Strombus gigas, Strombus costatus and Strombus pu Chakalall B. and Cochrane KL (1996). The Queen Conch fisheries in the Caribbea An approach to responsible fisheries mana Juan, Puerto Rico, 29-31 July 1996. Caribbean Fisheries Management Council. P (60-76). GSustainable Yield from Biomass data when catch and effort time series are not available. Fisheries Research, 8, p13-23. Macintyre and Aronson.1997. Field Guide book to the reefs of Belize. Proc. 8th Int. Coral Reef Sym. Rutzler, K. and Macintyre. I.G. 1982. The habitat distribution and community structure of the Barrier Reef comple Belize: Structure and Communities. Smithsonian Institution, Washington D.C. S


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e

ewfik A. (1996). An assessment of the Biological Characteristics, Abundance, and

ersity, Canada.

Stoner, A.W. and Ray-Culp, M.(2000) Distribution for Allee in an over-harvested marin gastropod:density-dependent mating and egg production. T Potential Yield of the Queen conch (Strombus gigas L.) Fishery on the Pedro Bank Off Jamaica. MS Thesis. Acadia Univ Wood EM. (1995). Study of the Fishery for Queen conch in Haiti. Marine Conservation Society. Ross-on Wye, Uk. 57 pp.


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nnex 1:

A


29________________________________________________________________________ Conch Stock Assessment 2006

29

Annex 2:

Stock Assessment of the Queen Conch Population of Belize

Documents

Transcript of Stock Assessment of the Queen Conch Population of Belize