American Fisheries Society Symposium 50:141–151, 2007© Copyright by the American Fisheries Society 2007

141

Shark Nursery Grounds in Sapelo Island National EstuarineResearch Reserve, Georgia

CHRISTOPHER W. D. GURSHIN*

Normandeau Associates, Inc., 25 Nashua Road, Bedford, New Hampshire 03110-5500, USA

Abstract.—Data are lacking for shark nursery grounds along Georgia’s coast that would be usefulin development of species-specific fishery management plans. The purpose of this survey was todescribe the use of Sapelo Island National Estuarine Research Reserve, Georgia as nursery groundsfor sharks. Relative abundance, length–frequency distribution, spatial and temporal occurrence, andfeeding habits were determined for Atlantic sharpnose sharks Rhizoprionodon terraenovae (N =305), blacktip sharks Carcharhinus limbatus (N = 65), finetooth sharks C. isodon (N = 38), andbonnetheads Sphyrna tiburo (N = 16) from 35 trammel net collections during June–August 1997.Catch per unit effort (CPUE) of Atlantic sharpnose sharks (26.4 sharks/h) was significantly higherthan CPUE of blacktip sharks (5.6 sharks/h), finetooth sharks (3.3 sharks/h), and bonnetheads (1.4sharks/h) for the entire study. Atlantic sharpnose sharks were significantly more abundant in earlyJuly (81.8 sharks/h) than in other periods in the summer season. In general, the trend of relativeabundance (CPUE) for each species was higher in July than other months. All species occurredthroughout most of the sampling area except in upper Duplin River for blacktip and finetooth sharksand middle Duplin River for finetooth sharks. Mean CPUE of Atlantic sharpnose sharks was signifi-cantly higher than CPUE of all other species in Doboy Sound and CPUE of finetooth sharks andbonnetheads in lower Duplin River. Blacktip sharks (7.6 sharks/h) were significantly more abundantthan bonnetheads (0.3 sharks/h) in Doboy Sound. Water temperature and salinity during capturewere 25–32°C and 22–31 parts per thousand (ppt) for Atlantic sharpnose sharks, 22–31°C and 22–26 ppt for blacktip sharks, 25–30°C and 22–26 ppt for finetooth sharks, and 23–30°C and 23–26 pptfor bonnetheads. Atlantic sharpnose, blacktip, and finetooth sharks were mostly represented byyoung-of-the-year (YOY) individuals. A qualitative analysis of stomach contents suggested thatteleosts formed the majority of the diet for blacktip and finetooth sharks, a variety of prey items,including teleosts, penaeids, stomatopods, cephalopods, and brachyurans for Atlantic sharpnosesharks, and exclusively crustaceans, particularly blue crabs Callinectes sapidus, for bonnetheads.The length–frequency distribution and occurrence of YOY- and juvenile-sized individuals feedingon a variety of prey common to the estuary indicates the use of this estuarine system as primary andsecondary nursery grounds for Atlantic sharpnose, blacktip, and finetooth sharks and as a secondarynursery ground for bonnetheads during the summer of 1997.

* E-mail: cgurshin@normandeau.com

Introduction

More research to gain biological and ecologicalinformation on shark pupping and nurserygrounds will help provide managers with the dataneeded to develop species-specific fishery man-agement plans (National Marine Fisheries Service1993, 1999). Some sharks migrate and give birthin nursery areas, typically where food is abun-dant and protection from predators is assured(Springer 1967). Habitats such as marsh, sea grass,and mangrove ecosystems offer shark neonatesprotection from cannibalistic or large predatoryadult sharks and an abundance of prey (Branstetter1990; Castro 1993a). Simpfendorfer and Milward

(1993) showed that Cleveland Bay, Australia wasused as a nursery habitat with abundant prey forat least eight shark species that were seasonallydistributed. Parsons (1983) suggested that thebarrier island systems of the northern Gulf ofMexico serve as nursery grounds for Atlanticsharpnose sharks Rhizoprionodon terraenovaeafter collection of neonates in the shallow watersand observing a seasonal inshore–offshore migra-tion of adult female Atlantic sharpnose sharks.

Identification and description of shark nurs-ery grounds in the estuarine and coastal waters ofGeorgia is limited. Dahlberg and Heard (1969)collected nine species of shark from Georgiasound waters, including Sapelo Island waters. Inthe neighboring state of South Carolina, Castro(1993a, 1996) reported that Bulls Bay, an exten-

142 GURSHIN

sive estuarine system characterized by saltmarshes, barrier islands, and a labyrinth of tidalcreeks, serves as a nursery area for blacknosesharks Carcharhinus acronotus, spinner sharksC. brevipinna, finetooth sharks C. isodon,blacktip sharks C. limbatus, sandbar sharks C.plumbeus, dusky sharks C. obscurus, and Atlan-tic sharpnose sharks.

The study of food habits in sharks is impor-tant in determining their role in the trophic dy-namics of a marine system. Differences in feedingecology of sharks among different seasons, habi-tats, and life stages are important to evaluatecompetition and predation. Dietary needs changeamong young of the year, juveniles, and adults asshown in the sandbar shark (Stillwell and Kohler1993). Diet overlap of species-life stage combi-nations of Atlantic sharpnose, blacktip, finetooth,and spinner sharks alleviated competition pres-sure from nonlimiting prey abundance inApalachicola Bay, Florida and may be evidenceof resource partitioning (Bethea et al. 2004).

The goal of this study is to sample the sharksin the protected salt marshes, estuaries, and coastalwaters of Sapelo Island National Estuarine Re-search Reserve, Georgia and evaluate its use as asummer nursery and feeding habitat for sharks.Primary nursery grounds are defined as habitatwhere parturition and young of the year occur,and secondary nursery grounds are where olderjuveniles occur. Relative abundance, species rich-ness, life stages, and food habits are described bythis survey.

Methods

The Sapelo Island National Estuarine ResearchReserve is an estuarine system dominated bySpartina alterniflora marshes, protected by abarrier island (Figure 1). The reserve covers 24.7km2 of marsh and land. The marsh soil is com-posed of alkaline clay with thin sand layers.Sapelo Island, fourth largest in Georgia, is a bar-rier island with an estuary that receives freshwa-ter input from runoff and rivers. The Duplin Riveris a 12-km-long tidal creek with an estuary of13.3 km2. The Duplin River is connected to theAtlantic Ocean by Doboy Sound. Average tidalrange is about 2.3 m with tidal fluctuationsgreatly affected by wind direction and intensity.The channel of the Duplin River is approxi-mately 4–5 m in depth with several areas deeper

than 10 m. The depth of Doboy Sound is ap-proximately 7–10 m.

Twelve Duplin River and three DoboySound stations were sampled using a stratifieddesign (Figure 1). Collections were made two orthree times a week from June through August1997. A monofilament trammel net (183 × 3.0m, 6.35-cm stretched mesh on the inner panel,and 35.6-cm stretched mesh on outer panels) wasused to sample at the last 2 h of ebb tide. Bottomand surface salinity, bottom and surface tempera-ture, and depth were recorded for each sample.Live sharks were identified, sexed, measured,and released. Those that died during capturewere placed on ice for further analysis of mor-phological characteristics and stomach contents;some specimens in large catches were not mea-sured or sexed. Sharks were staged as young ofthe year (age 0, including neonates with un-healed or healed umbilical scars), juveniles (age1+) or adults based on size (Clark and vonSchmidt 1965; Branstetter and Shipp 1980;Branstetter 1981, 1987a, 1987b; Parsons 1983,1985, 1993; Compagno 1984; Castro 1993a,1993b, 1996; Carlson et al. 2003; Lombardi-Carlson et al. 2003).

Stomach contents were removed from theanterior end of the stomach to the anterior end ofthe pyloris, weighed, and identified to the lowesttaxon possible. Stomach contents were reportedas percentage frequency of occurrence (%O; esti-

FIGURE 1. Sapelo Island, Georgia is shown with upper(U), middle (M), lower (L) Duplin River and DoboySound (D) marked as sampling areas, each with threesampling stations. Boundaries of Sapelo Island NationalEstuarine Research Reserve are outlined by dashed lines.

SHARK NURSERY GROUNDS IN SAPELO ISLAND NATIONAL ESTUARINE RESEARCH RESERVE, GEORGIA 143

mated as the proportion of stomachs that con-tained a specific prey type), percentage by num-ber (%N; calculated as the number within a preycategory divided by the total number of preyitems found in the stomachs), and percentage bywet weight (%W; estimated as the proportion of aprey type that appeared in the stomachs accord-ing to weight). Index of relative importance (IRI)was calculated following the formula given byPinkas et al. (1971). The percentage index of rela-tive importance (%IRI) was calculated using theequation given by Cortés (1997). Due to lowsamples sizes, these indices served as a qualita-tive analysis to provide a cursory look at preycomposition and importance of prey items.

To analyze trends in relative abundance,catch per unit effort (CPUE) was calculated asthe number of sharks caught per net hour of soaktime. Nonparametric methods were used becauseCPUE values were not normally distributed. AKruskal–Wallis test was used to test for differ-ences in CPUE for each species among temporal(early June, late June, early July, late July, andearly August) and spatial (upper, middle, lowerDuplin River and Doboy Sound) effects (α =0.05; Sokal and Rohlf 1995). Temporal and spa-tial effects were analyzed separately because notall regions were sampled for each period. A sig-nificant test was followed by a Tukey-Kramermultiple pairwise comparison test of rankedmeans (SAS Institute, Inc. 1999). Comparisonsof CPUE were made among species within eachperiod and region as well as for the entire studyarea (periods and regions pooled) during theentire sampling season. Bottom and surface tem-peratures and salinities, and depth were tested

for correlation with CPUE by Spearman’s rank-order correlation coefficient.

Results and Discussion

Atlantic sharpnose sharks (N = 305), blacktipsharks (N = 65), finetooth sharks (N = 38), andbonnetheads Sphyrna tiburo (N = 16) were col-lected in 35 trammel net collections from 6 June1997–10 August 1997 in the Duplin River andDoboy Sound of Sapelo Island National EstuarineResearch Reserve (Table 1). Mean CPUE of Atlan-tic sharpnose sharks was significantly higher thanCPUE of blacktip, finetooth, and bonnetheadsharks for the entire study area from June throughAugust (Table 1; P < 0.05). Bottom and surfacetemperature and salinities, and depth were not cor-related with CPUE (P > 0.05).

Atlantic sharpnose shark

Atlantic sharpnose sharks were found in all partsof the sample area with the majority in the lowerDuplin River and Doboy Sound. Catch per uniteffort of Atlantic sharpnose sharks was signifi-cantly higher in early July compared to late July,late June, early August, and early June in 1997among all regions combined (P < 0.05; Table 1).Mean CPUE of Atlantic sharpnose sharks was sig-nificantly higher than CPUE of finetooth sharksin late June, finetooth and blacktip sharks in earlyJuly, and all other species in late July (P < 0.05;Figure 2). Mean CPUE was significantly higherthan CPUE of finetooth sharks and bonnetheadsin lower Duplin River and all other species inDoboy Sound (P < 0.05; Figure 3). This specieswas caught at all depths (0–5 m) in portions of

TABLE 1. Total catch (N) and mean catch per unit effort (CPUE, number per hour soak time) of four shark speciescaught by trammel net collections in the Duplin River and Doboy Sound of Sapelo Island National Estuarine ResearchReserve, Georgia during June–August 1997.

Atlanticsharpnose Blacktip Finetooth Bonnethead

Time or area shark shark shark shark(number of sets) N CPUE N CPUE N CPUE N CPUE

Early June (5) 6 3.6 4 2.4 1 0.6 2 1.2Late June (7) 43 18.6 7 3.0 0 0.0 3 1.3Early July (6) 162 81.8 27 13.6 28 14.1 4 2.0Late July (10) 82 24.8 17 5.2 3 0.9 0 0.0Early August (7) 12 5.2 10 4.3 6 2.6 7 3.0Upper Duplin River (3) 13 13.1 0 0.0 0 0.0 1 1.0Middle Duplin River (4) 15 11.4 12 9.1 0 0.0 2 1.5Lower Duplin River (16) 206 39.6 22 4.4 19 4.4 13 2.3Doboy Sound (12) 71 17.2 31 7.6 19 3.8 1 0.3Total (35) 305 26.4 65 5.6 38 3.3 16 1.4

144 GURSHIN

FIGURE 2. Comparison of catch per unit effort (CPUE) from trammel net collections among Atlantic sharpnosesharks, blacktip sharks, finetooth sharks, and bonnetheads within early June (number of sets = 5), late June (7), earlyJuly (6), late July (10) and early August 1997 (7) for all regions of the Sapelo Island National Estuarine ResearchReserve combined. Significant differences in CPUE from a Tukey-Kramer multiple pairwise comparison test ofranked means are separated by different letters (P < 0.05). Error bars represent SE of the mean CPUE.

FIGURE 3. Comparison of catch per unit effort (CPUE) from trammel net collections among Atlantic sharpnosesharks, blacktip sharks, finetooth sharks, and bonnetheads within upper (number of sets = 3), middle (4), and lowerDuplin River (16), and Doboy Sound (12) of the Sapelo Island National Estuarine Research Reserve for all periods ofthe 1997 summer season combined. Significant differences in CPUE from a Tukey-Kramer multiple pairwise com-parison test of ranked means are separated by different letters (P < 0.05). Error bars represent SE of the mean CPUE.

0

10

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Upper Duplin R. Middle Duplin R. Lower Duplin R. Doboy Sound

Region

CP

UE

(sh

arks

/h)

Atlantic sharpnose shark

Blacktip shark

Finetooth shark

Bonnethead

AB

A

A

BB

BC

CB

0

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40

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140

Early June Late June Early July Late July Early August

Period

CP

UE

(sh

arks

/h)

Atlantic sharpnose sharkBlacktip sharkFinetooth sharkBonnethead

A

AB ABB

A

AB

B

BA

BBB

SHARK NURSERY GROUNDS IN SAPELO ISLAND NATIONAL ESTUARINE RESEARCH RESERVE, GEORGIA 145

the estuary with bottom water temperatures of25–32°C, bottom salinities of 23–26 parts perthousand (ppt), surface water temperatures of 25–32°C, and surface salinities of 22–31 ppt. Theseenvironmental conditions were not correlatedwith CPUE (P > 0.05).

The mean total length (TL) was 395 ± 83.7mm (±SD) and the median was 387 mm TL (N =169), indicating that the majority of the speci-mens caught were young of the year (Figure 4).Many young of the year were observed with un-healed and healed umbilical scars. Specimensranged from 258 to 970 mm TL. Only two speci-mens were greater than 900 mm TL.

According to all five indices of stomach con-tent analyses, bony fishes were the most importantfood items followed by penaeids (Table 2). In thesesamples, bony fishes included menhaden Brevoor-tia sp., anchovies Anchoa sp., blennids, and otherunidentified teleosts. However, Atlantic sharpnosesharks also foraged on nonteleost prey as indicatedby occasional squid, carideans, stomatopods, anddecapods found in their stomachs.

Other studies show the diet of Atlanticsharpnose sharks is consistent with the prey com-position found in this study. Stomachs from manyneonates caught in shrimp trawls during June and

July near Dauphin Island, Alabama contained fishand shrimp of the genus Sicyonia (Branstetter1981). Clark and von Schmidt (1965) found stom-achs of adult specimens from Florida to containfishes such as silver jenny Eucinostomus gula,monoacanthids, kingfish Menticirrhus sp., clu-peids, menhaden, and shrimps. Ophichthids, sil-versides Menidia sp., labrids, small jacks Caranxsp., croakers Micropogonias sp., toadfish Ospanussp., and annelids have also been reported for thediet of the Atlantic sharpnose shark (Compagno1984). In Apalachicola Bay, Florida, young-of-the-year (YOY) Atlantic sharpnose sharks prima-rily feed on shrimp, and juveniles and adults onteleosts (Bethea et al. 2004). The heterogenousdiet of Atlantic sharpnose sharks in the northwestAtlantic Ocean is indicative of generalized feed-ers (Gelsleichter at al. 1999).

Blacktip shark

A total of 65 blacktip sharks were collected fromthe study area making this the second most abun-dant shark in this survey (Table 1). Blacktip sharkswere collected in all sample areas except the up-per Duplin River. Relative abundance (CPUE) ofblacktip sharks was highest in July, but no sig-

FIGURE 4. Total length-frequency distribution of Atlantic sharpnose sharks caught in the Sapelo Island NationalEstuarine Research Reserve during summer months of 1997. The total length range for life stages are indicated by aclosed bar (neonate with umbilical scars), closed and open bars (young of the year, age 0), and a bracket (juvenile, age1+; Branstetter 1981, 1987a; Parsons 1983, 1985).

Atlantic sharpnose shark

0

20

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<250

250-2

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400-4

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Total length (mm)

Num

ber o

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N = 169

146 GURSHIN

nificant differences were detected (P > 0.05; Table1). Similarly, blacktip sharks showed increasedabundance in June and July within the north-central Gulf of Mexico (Branstetter 1981). MeanCPUE of blacktip sharks was significantly higherthan CPUE of bonnetheads in Doboy Sound (P <0.05; Figure 3). Blacktip sharks were collected atdepths of 0–5 m in waters with bottom water tem-peratures of 22–30°C, bottom salinities of 23–26ppt, surface water temperatures of 22–31°C, andsurface salinities of 22–26 ppt.

A random sample of 16 blacktip sharks rangedfrom 559 to 1,190 mm TL (1.0–9.5 kg), with amean of 723 ± 142 mm TL and median of 700 mmTL. Mature adult blacktip sharks were not caughtduring this survey, but they may have evaded thetrammel nets by using the unsampled deep chan-nels. From the length–frequency distribution, thesummer population of blacktip sharks appearedto consist primarily of young of the year and smalljuveniles, suggesting that the estuary system ofSapelo Island, Georgia served as primary and sec-ondary nursery habitats (Figure 5).

Blacktip sharks were found to prey mostlyupon teleosts, particularly menhaden (Table 2).This diet is consistent with the diet of primarilysciaenids for young of the year and clupeids forjuvenile blacktip sharks in Apalachicola Bay,Florida (Bethea et al. 2004). Castro (1996) found

the diet of blacktip sharks in Bulls Bay, SouthCarolina to consist of mainly Atlantic menhadenB. tyrannus, cownose rays Rhinoptera bonasus,Atlantic sharpnose sharks, and bonnetheads. Castro(1996) reported less than 2% of the blacktip sharkstomachs contained spot Leiostomus xanthurus,Spanish mackerel Scomberomorus maculatus, At-lantic croaker M. undulatus, oyster toadfish O. tau,gafftopsail catfish Bagre marinus, or floundersParalichthys spp. In addition to those prey speciespreviously reported, blacktip sharks have beenknown to eat jacks, common snook Centropomusundecimalis, striped burrfish Chilomycterusschoepfii, hardhead catfish Ariopsis felis (alsoknown as Arius felis), trunkfish Lactophrystrigonis, pinfish Lagodon rhomboides, Atlanticthreadfin Polydactylus octonemus, anchovies,longspine porgy Stenotomus caprinus, Gulf but-terfish Peprilus burti, and invertebrates (Clark andvon Schmidt 1965; Branstetter 1981).

The occurrence of young of the year and ju-veniles in many regions of the study area duringthe middle of the summer season is consistentwith migratory patterns in other regions of thesoutheastern United States coast. Castro (1996)reports that gravid female blacktip sharks migratefrom southern waters in early May to June to theshallow coastal habitats of the Carolinas andFlorida to deposit their offspring. Capture of

TABLE 2. Prey composition and relative importance of prey from stomach content analysis of four species fromSapelo Island National Estuarine Research Reserve, Georgia during the summer months of 1997 (%N = percentage bynumber; %O = percentage frequency of occurrence; %W = percentage by weight; IRI = index of relative importance;%IRI = percentage index of relative importance).

Species (N =) Prey category %N %W %O IRI %IRI

Atlantic sharpnose shark (86) Teleostei 46.3 67.0 37.2 4214.8 62.20Penaeidae 7.5 8.5 7.0 112.0 1.65Teuthoidea 2.5 0.9 2.3 7.8 0.12Stomatopoda 1.3 1.2 1.2 3.0 0.04Brachyura 1.3 0.7 1.2 2.4 0.04Caridea 1.3 1.3 1.2 3.1 0.05Unidentified 40.0 25.4 37.2 2,432.9 35.90

Blacktip shark (14) Brevoortia sp. 54.5 48.0 35.7 3,660.8 65.92Other Teleostei 27.3 42.7 21.4 1,499.0 26.99Unidentified 18.2 9.4 14.3 393.5 7.09

Finetooth shark (18) Brevoortia sp. 21.7 45.1 27.8 1,857.0 25.55Other Teleostei 56.5 41.1 50.0 4,880.0 67.13Teuthoidea 4.3 6.6 5.6 61.3 0.84Penaeidae 4.3 0.2 5.5 24.7 0.34Unidentified 13.0 7.1 22.2 446.2 6.14

Bonnethead (5) Portunidae 50.0 75.9 80.0 10,075.4 87.18Other Brachyura 20.0 16.0 20.0 719.2 6.22Penaeidae 10.0 3.6 20.0 272.2 2.36Stomatopoda 10.0 2.4 20.0 248.1 2.15Xanthidae 10.0 2.1 20.0 241.7 2.09

SHARK NURSERY GROUNDS IN SAPELO ISLAND NATIONAL ESTUARINE RESEARCH RESERVE, GEORGIA 147

gravid females will be necessary to support thatneonates are born within the areas sampled ratherthan immigrating from offshore. Castro (1996)found that blacktip sharks disappeared from thenursery grounds of Bulls Bay, South Carolina inearly to mid-October when water surface tempera-tures dropped below 21°C.

Finetooth Shark

In this study, finetooth sharks (N = 38) were onlycaught in the lower Duplin River and DoboySound (Table 1). Peak abundance occurred at theend of June and the first half of July (Table 1).There were no significant differences in meanCPUE of finetooth sharks among periods or re-gions (P > 0.05). Finetooth sharks were signifi-cantly less abundant from early June through lateJuly (P < 0.05; Figure 2). Mean CPUE of finetoothsharks was significantly lower than CPUE of At-lantic sharpnose sharks in lower Duplin River andDoboy Sound but was significantly higher thanCPUE of bonnetheads in Doboy Sound (P < 0.05;Figure 3). Finetooth sharks were present in estua-rine waters with bottom water temperatures of 25–30°C, bottom salinities of 24–26 ppt, surfacewater temperature of 25–30°C, and surface salini-ties of 22–26 ppt. Castro (1993b) reported

finetooth sharks appear off South Carolina whenwater warmed above 20°C. Collections later inthe year may answer whether these species arereplaced by other species during cooler months.These specimens ranged from 537 to 980 mm TL(0.8–5.4 kg), with a mean of 619 ± 114 mm TLand median of 646 mm TL. The majority offinetooth sharks sampled were young of the yearor juvenile-sized individuals (Figure 6). Severalindividuals were observed with umbilical scarsindicative of neonates. The largest male at 914mm TL and a female at 980 mm TL were both lessthan the size at maturity, suggesting that the es-tuary serves as a nursery habitat for YOY and ju-venile finetooth sharks.

Stomachs from 18 finetooth sharks were ex-amined for prey items, which included teleostsand invertebrates (Table 2). Castro (1993b) foundthat the major prey items in the diet of finetoothsharks consisted of Atlantic menhaden, spot,penaeids, Spanish mackerel, mullet Mugil sp., andjuvenile Atlantic sharpnose sharks.

Bonnethead

There was a total catch of 16 bonnetheads.Bonnetheads occurred in all parts of the tidal

Blacktip shark

0

1

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6

500-5

49

550-5

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-1049

1050

-1099

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-1149

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-1199

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-1249

>125

0

Total length (mm)

Num

ber o

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ens

N = 16

FIGURE 5. Total length–frequency distribution of blacktip sharks caught in the Sapelo Island National EstuarineResearch Reserve during summer months of 1997. The total length range for life stages are indicated by a closed bar(neonate with umbilical scars), closed and open bars (young of the year, age 0) and a bracket (juvenile, age 1+; Clarkand von Schmidt 1965; Branstetter 1981, 1987b; Castro 1993a, 1996).

148 GURSHIN

Duplin River, but none were caught in late July(Table 1). No temporal patterns were found forthe summer season of 1997 (Table 1). Mean CPUEof bonnetheads was significantly less than theCPUE of Atlantic sharpnose sharks in DoboySound and lower Duplin River and blacktipsharks in Doboy Sound (P < 0.05; Figure 3).Bonnetheads were found at depths of 0–5 m inestuarine waters with bottom water temperaturesof 23–29°C, bottom salinities of 23–26 ppt, sur-face water temperatures of 25–31°C, and surfacesalinities of 23–26 ppt. There was no significantcorrelation between CPUE and environmentalconditions (P > 0.05).

A random subsample of seven specimensmeasured from 537 to 644 mm TL, with a mean of590 ± 41.5 mm TL and median of 588 mm TL(Figure 5). Total wet weight ranged from 0.5 to1.1 kg. Based on their size, these bonnetheadswere estimated to be older juveniles (>age 1+)and adults (Figure 7).

Stomach contents analysis of five bonnet-heads indicated that during the summer of 1997,the diet consisted exclusively of crustaceans (i.e.,portunids, particularly blue crabs Callinectessapidus, other brachyurans such as calico crabsHepatus epheliticus, penaeids, stomatopods, and

xanthids) (Table 2). A diet dominated by bluecrabs was reported for populations from TampaBay and Charlotte Harbor on Florida’s west coast(Cortés et al. 1996). In addition to the crustaceansobserved in this study, mollusks, includingcephalopods and gastropods, sea grasses, teleo-sts and horseshoe crabs Limulus polyphemus, havealso been found in stomach contents of bonnet-heads (Cortés et al. 1996).

Conclusions

Atlantic sharpnose, blacktip, finetooth, andbonnethead sharks were observed to inhabit theshallow waters of Sapelo Island National Estua-rine Research Reserve, Georgia in the summermonths of 1997. Collection of large numbers ofYOY and juvenile Atlantic sharpnose, blacktip,and finetooth sharks indicated that these speciesused these sampled areas as primary and second-ary nursery grounds during the summer. This habi-tat may have only served as a secondary nurseryground for bonnetheads in 1997 as indicated bythe occurrence of only juvenile- and adult-sizedindividuals. The analysis of stomach contents re-vealed teleosts formed the majority of the diet forYOY and juvenile blacktip and finetooth sharks, a

Finetooth shark

0

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4

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450-4

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Total length (mm)

Num

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N = 18

FIGURE 6. Total length–frequency distribution of finetooth sharks caught in the Sapelo Island National EstuarineResearch Reserve during summer months of 1997. The total length range for life stages are indicated by a closed bar(neonate with umbilical scars), closed and open bars (young of the year, age 0), and a bracket (juvenile, age 1+;Branstetter and Shipp 1980; Castro 1993b; Carlson et al. 2003).

SHARK NURSERY GROUNDS IN SAPELO ISLAND NATIONAL ESTUARINE RESEARCH RESERVE, GEORGIA 149

variety of prey items, including teleosts, penaeids,stomatopods, cephalopods, and brachyurans forAtlantic sharpnose shark, and exclusively crusta-ceans, particularly blue crabs, for bonnetheads. Theoccurrence of young of the year feeding on a vari-ety of common prey suggests that the use of thisestuarine system as a foraging area.

Relative abundance appeared to be higher insome areas during certain periods of the season forsharks. Atlantic sharpnose sharks were significantlymore abundant than blacktip, finetooth, andbonnethead sharks for the entire study. In general,CPUE trends increased from early June and peakedin July for most species except for bonnetheads.Catch per unit effort of Atlantic sharpnose sharkswas significantly higher than CPUE of finetoothsharks in late June, finetooth sharks and bonnet-heads in early July, and all species in late July. Thelower Duplin River and Doboy Sound appeared tosupport a higher abundance of Atlantic sharpnosesharks than other species. Bonnetheads were leastabundant in Doboy Sound.

Environmental conditions did not appear toaffect distribution of Atlantic sharpnose, blacktip,finetooth, and bonnethead sharks. Water tempera-ture and salinity during sampling fluctuated 10°Cand 9 ppt, respectively, but did not appear to affect

CPUE. Water temperature ranged from 22°C to32°C and salinity ranged from 22 to 31 ppt. Youngof the year and juveniles of these four species werecaught at depths of 5 m or less but may have alsooccurred in deeper waters if collections were madewith different gear. However, larger predatorysharks were not caught within sampled depths,which suggest these shallow estuarine waters mayprovide refuge for young of the year and juvenilesfrom predation.

Tidal marshes and other coastal habitats needto be evaluated for their importance in sustain-ing shark populations and development of spe-cies-specific fisheries management plans. Atlanticsharpnose, blacktip, finetooth, and bonnetheadsharks are regulated as either small or large coastalsharks under the Final Fishery Management Planfor Atlantic Tuna, Swordfish and Sharks (NMFS1999), which calls for the need of more biologi-cal information on primary and secondary nurs-ery grounds for better management. Low fishingpressure, direct or indirect, in these protected tidalmarshes that appear to offer foraging areas andrefuge from predation may have an important rolein sustaining these sharks in southeastern UnitedStates. Research throughout the year with mul-tiple gear types might show evidence of additional

Bonnethead

0

1

2

3

350-3

74

375-3

99

400-4

24

425-4

49

450-4

74

350-3

74

375-3

99

400-4

24

425-4

49

450-4

74

475-4

99

500-5

24

525-5

49

550-5

74

575-5

99

600-6

24

625-6

49

650-6

74

675-6

99>7

00

Total length (mm)

Num

ber o

f spe

cim

ens

N = 7

FIGURE 7. Total length–frequency distribution of bonnetheads caught in the Sapelo Island National EstuarineResearch Reserve during summer months of 1997. The total length range for life stages are indicated by a closed bar(neonate with umbilical scars), closed and open bars (young of the year, age 0) and a bracket (juvenile, age 1+; Clarkvon Schmidt 1965; Branstetter 1981; Compagno 1984; Parsons 1993).

150 GURSHIN

species that use these estuarine or coastal waters ofGeorgia as nursery grounds. However, this studyshows evidence that Sapelo Island National Es-tuarine Research Reserve of coastal Georgia servesas nursery and feeding habitat for Atlanticsharpnose, blacktip, finetooth, and bonnetheadsharks during the summer months in 1997. Furtherresearch is needed to determine the importance ofthis estuarine system as shark nursery habitat.

Acknowledgments

I thank my mentors L. R. Barbieri and S. K. Lowerre-Barbieri for their expertise, advisement, and op-portunity to conduct the shark research in Georgia.This opportunity was made possible through the1997 University of Georgia Marine Institute Re-search Internship. Data collection in Georgia wouldnot have been possible without the generous helpof G. Breed, M. K. Knowlton, J. R. Flanders, and C.Cotton. I also thank all those who helped editingportions of this manuscript.

References

Bethea, D. M., J. A. Buckel, and J. K. Carlson. 2004.Foraging ecology of the early life stages of foursympatric shark species. Marine Ecology ProgressSeries 268:245–264.

Branstetter, S. 1981. Biological notes on the sharks of thenorth central Gulf of Mexico. Contributions in Ma-rine Science 24:13–34.

Branstetter, S. 1987a. Age and growth validation of new-born sharks held in laboratory aquaria, with com-ments on the life history of the Atlantic sharpnoseshark, Rhizoprionodon terraenovae. Copeia 2:291–300.

Branstetter, S. 1987b. Age and growth estimates forblacktip, Carcharhinus limbatus, and spinner, C.brevipinna, sharks from the northwestern Gulf ofMexico. Copeia 1987:964–974.

Branstetter, S. 1990. Early life-history implications ofselected carcharhinoid and lamnoid sharks of thenorthwest Atlantic. Pages 17–28 in H. L. Pratt, Jr., S.H. Gruber, and T. Taniuchi, editors. Elasmobranchsas living resources: advances in the biology, ecol-ogy, systematics, and the status of the fisheries. NOAATechnical Report NMFS 90.

Branstetter, S., and R. L. Shipp. 1980. Occurrence of thefinetooth shark, Carcharhinus isodon, off DauphinIsland, Alabama. Fishery Bulletin 78(1):177–179.

Carlson, J. K., E. Cortés, and D. M. Bethea. 2003. Lifehistory and population dynamics of the finetoothshark (Carcharhinus isodon) in the northeastern Gulfof Mexico. Fishery Bulletin 101:281–292.

Castro, J. 1993a. The shark nursery of Bulls Bay, SouthCarolina, with a review of the shark nurseries of the

southeastern coast of the United States. Environmen-tal Biology of Fishes 38:37–48.

Castro, J. 1993b. The biology of the finetooth shark,Carcharhinus isodon. Environmental Biology ofFishes 36:219–232.

Castro, J. 1996. Biology of the blacktip shark,Carcharhinus limbatus, off the southeastern UnitedStates. Bulletin of Marine Science 59:508–522.

Clark, E., and K. von Schmidt. 1965. Sharks of the cen-tral gulf coast of Florida. Bulletin of Marine Science15:13–83.

Compagno, L. J. V. 1984. FAO species catalogue of theworld. Volume 4. Sharks of the world. Part 2:Carcharhiniformes. FAO Fisheries Synopsis 125.

Cortés, E. 1997. A critical review of methods of studyingfish feeding based on analysis of stomach contents:application to elasmobranch fishes. Canadian Jour-nal of Fisheries and Aquatic Sciences 54:726–738.

Cortés, E, C. A. Manire, and R. E. Hueter. 1996. Diet,feeding habits, and diel feeding chronology of thebonnethead shark, Sphyrna tiburo, in southwestFlorida. Bulletin of Marine Science 58:353–367.

Dahlberg, M. C., and R. W. Heard, III. 1969. Observa-tions on elasmobranchs from Georgia. QuarterlyJournal of Florida Academy of Sciences 32:21–25.

Gelsleichter, J., J. A. Musick, and S. Nichols. 1999. Foodhabits of the smooth dogfish, Mustelus canis, duskyshark, Carcharhinus obscurus, Atlantic sharpnoseshark, Rhizoprionodon terraenovae, and the sandtiger, Carcharias taurus, from the northwest Atlan-tic Ocean. Environmental Biology of Fishes 54:205–217.

Lombardi-Carlson, L. A., E. Cortés, G. R. Parsons, andC. A. Manire. 2003. Latitudinal variation in life-history traits of bonnethead sharks, Sphyrna tiburo,(Carcharhiniformes: Sphyrnidae) from the easternGulf of Mexico. Marine and Freshwater Research54:875–883.

National Marine Fisheries Service. 1993 Fishery man-agement plan for sharks of the Atlantic Ocean.USDOC/NOAA/NMFS, Washington, D.C.

National Marine Fisheries Service. 1999. Final fisherymanagement plan for Atlantic tunas, swordfish, andsharks. USDOC/NOAA/NMFS, Silver Spring, Mary-land.

Parsons, G. R. 1983. The reproductive biology of theAtlantic sharpnose shark, Rhizoprionodon terrae-novae (Richardson). Fishery Bulletin 81:61–73.

Parsons, G. R. 1985. Growth and age estimation of theAtlantic sharpnose shark, Rhizoprionodon terrae-novae: a comparison of techniques. Copeia 1:80–85.

Parsons, G. R. 1993. Age determination and growth ofthe bonnethead shark Sphyrna tiburo: a comparisonof two populations. Marine Biology 117:23–31.

Pinkas, L. M., S. Oliphant, and I. L. K. Iverson. 1971.Food habits of albacore, bluefin tuna and bonito inCalifornian waters. California Fish and Game 142:1–105.

Simpfendorfer, C. A., and N. E. Milward. 1993. Utilisation

SHARK NURSERY GROUNDS IN SAPELO ISLAND NATIONAL ESTUARINE RESEARCH RESERVE, GEORGIA 151

of a tropical bay as a nursery area by sharks of thefamilies Carcharhinidae and Sphyrnidae. Environ-mental Biology of Fishes 37:337–345.

SAS Institute, Inc. 1999. SAS/STAT user’s guide, version8. Volumes 1–5. SAS Publishing, Cary, North Caro-lina.

Sokal, R. R., and F. J. Rohlf. 1995. Biometry. Freeman,New York.

Springer, S. 1967. Social organization of shark popula-tions. Pages 149–174 in P. Gilbert, R. Mathewson,and D. Rall, editors. Sharks, skates and rays. JohnHopkins Press, Baltimore, Maryland.

Stillwell, C. E., and N. E. Kohler. 1993. Food habits ofthe sandbar shark Carcharhinus plumbeus off theU.S. northeast coast, with estimates of daily ration.Fishery Bulletin 91:138–150.