Carcharhinus Limbatus Research Articles

La pesquería de tiburones oceánicos-costeros en los litorales de Colima, Jalisco y Michoacán

Shark fishery is one of the most important activities in the Mexican Pacific coast, nevertheless, there is few data available about the specific captures done by the fleet along the coast. This study describes fishery biology aspects of the shark species catched by the semi-industrial long-line fleet of Manzanillo. Monthly samplings were made on board of these vessels during an annual period from April 2006 to April 2007. Captured species composition (n = 1 962 organisms) was represented by nine species. The one that sustains this fishery was Carcharhinus falciformis (88.12%), followed by Prionace glauca (8.21%). Low frequency species were represented by Sphyrna zygaena (1.78%), Alopias pelagicus (0.82%), Carcharhinus longimanus (0.45%). Furthermore, rare species were Alopias superciliosus (0.35%), Carcharhinus leucas (0.1%), Carcharhinus limbatus (0.1%) and Isurus oxyrinchus (0.05%). Fishery activity affected principally (60-92.70%) young males of C. falciformis, S. zygaena, C. longimanus and I. oxyrinchus; adult males (56-75%) of A. pelagicus, A. superciliosus, and C. limbatus; for P. glauca there were primarily female adults. For all the species found, females showed the bigger sizes when compared to males (with the exception of S. zygaena, that showed sexual dimorphism). Considering the lineal regressions made between precaudal length and total length, and, fork length and total length for C. falciformis, P. glauca, S. zygaena and A. pelagicus, the determination coefficients (r2) showed that both lengths can be useful to obtain the total length of fish with some damage or absence of its caudal fin. The estimated fecundity for C. falciformis was of 3-7 offspring/female of 30-45 cm LT (average of 40.57 +/- 2.03 cm LT); and for P. glauca 5-52 offspring/female of 5-18.6 cm LT (average of 11.61 +/- 0.21 cm LT). In the case of C. longimanus only one female was captured with a total of eight embryos, with an average of 45 cm LT each; for this reason we assumed that the fishery areas do not coincide with the nursery oness for this species. According to the information obtained, we concluded that C. falciformis has a concurrent cycle and P. glauca a consecutive biannual one.

Trophic organisation and predator–prey interactions among commercially exploited demersal finfishes in the coastal waters of the southeastern Arabian Sea

Trophic interactions in commercially exploited demersal finfishes in the southeastern Arabian Sea of India were studied to understand trophic organization with emphasis on ontogenic diet shifts within the marine food web. In total, the contents of 4716 stomachs were examined from which 78 prey items were identified. Crustaceans and fishes were the major prey groups to most of the fishes. Based on cluster analysis of predator feeding similarities and ontogenic diet shift within each predator, four major trophic guilds and many sub-guilds were identified. The first guild ‘detritus feeders’ included all size groups of Cynoglossus macrostomus, Pampus argenteus, Leiognathus bindus and Priacanthus hamrur. Guild two, named ‘Shrimp feeders’, was the largest guild identified and included all size groups of Rhynchobatus djiddensis and Nemipterus mesoprion, medium and large Nemipterus japonicus, P. hamrur and Grammoplites suppositus, small and medium Otolithes cuvieri and small Lactarius lactarius. Guild three, named ‘crab and squilla feeders’, consisted of few predators. The fourth trophic guild, ‘piscivores’, was mainly made up of larger size groups of all predators and all size groups of Pseudorhombus arsius and Carcharhinus limbatus. The mean diet breadth and mean trophic level showed strong correlation with ontogenic diet shift. The mean trophic level varied from 2.2 ± 0.1 in large L. bindus to 4.6 ± 0.2 in large Epinephelus diacanthus and the diet breadth from 1.4 ± 0.3 in medium P. argenteus to 8.3 ± 0.2 in medium N. japonicus. Overall, the present study showed that predators in the ecosystem have a strong feeding preference for the sergestid shrimp Acetes indicus, penaeid shrimps, epibenthic crabs and detritus.

Isolation and characterization of collagen from the cartilages of brownbanded bamboo shark ( Chiloscyllium punctatum) and blacktip shark ( Carcharhinus limbatus)

Acid soluble collagen (ASC) and pepsin soluble collagen (PSC) from the cartilages of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus) were isolated and characterized. ASC and PSC extracted from BBS cartilage showed the yields of 1.27 and 9.59 g/100 g (Based on dry weight), respectively, while yields of ASC and PSC from BTS cartilage were 1.04 and 10.30 g/100 g (based on dry weight), respectively. All collagens had protein as a major constituent with the trace amount of ash and fat. They contained glycine as the major amino acid with high contents of alanine, proline and hydroxyproline. Based on sodium dodecyl sulfate-polyacrylamide gel electrophoretic patterns and subunit compositions, all collagens more likely comprised 2 types of collagen, type I and II, and contained α- and β-chains as the major components. Peptide maps of those collagens from both species digested by V8-protease and lysyl endopeptidase were different and were completely different from those of type I collagen from calf skin. Thermal transition temperature of ASC from those collagens (36.28–36.73 °C) was slightly higher than their corresponding PSC (34.56–35.98 °C). From zeta potential analysis, isoelectric points (pI) of collagen from the cartilages of BBS and BTS were estimated to be from 6.53 to 7.03 and from 6.96 to 7.26, respectively. Fourier transform infrared (FTIR) spectra of both ASC and PSC were quite similar, suggesting that pepsin hydrolysis did not affect the secondary structure of collagen, especially triple-helical structure.

Towards better management of Australia's shark fishery: genetic analyses reveal unexpected ratios of cryptic blacktip species Carcharhinus tilstoni and C. limbatus

The common blacktip shark (Carcharhinus limbatus) and the Australian blacktip shark (C. tilstoni) are morphologically similar species that co-occur in subtropical and tropical Australia. In striking contrast to what has been previously reported, we demonstrate that the common blacktip shark is not rare in northern Australia but occurs in approximately equal frequencies with the Australian blacktip shark. Management of shark resources in northern Australia needs to take account of this new information. Species identification was performed using nucleotide sequences of the control, NADH dehydrogenase subunit 4 (ND4) and cytochrome oxidase I (COI) regions in the mitochondrial genome. The proportion of overall genetic variation (FST) between the two species was small (0.042, P < 0.01) based on allele frequencies at five microsatellite loci. We confirm that a third blacktip species (C. amblyrhynchoides, graceful shark) is closely related to C. tilstoni and C. limbatus and can be distinguished from them on the basis of mtDNA sequences from two gene regions. The Australian blacktip shark (C. tilstoni) was not encountered among 20 samples from central Indonesia that were later confirmed to be common blacktip and graceful sharks. Fisheries regulators urgently need new information on life history, population structure and morphological characters for species identification of blacktip shark species in Australia.

Distributions of Sharks across a Continental Shelf in the Northern Gulf of Mexico

AbstractDeclines in shark populations have sparked researchers and fishery managers to investigate more prudent approaches to the conservation of these fish. As managers strive to improve data collection for stock assessment, fisheries‐independent surveys have expanded to include data‐deficient areas such as coastal regions. To that end, a catch series from a nearshore survey off Alabama was combined with data from a concurrent offshore survey with identical methodology to examine the depth use of sharks across the continental shelf (2–366 m). The combined data set contained 22 species of sharks collected from 1995 to 2008: 21 species in the offshore data set (1995–2008) and 12 species in the nearshore data set (2006–2008). Depth was a significant factor determining species' distributions, primarily for Atlantic sharpnose Rhizoprionodon terraenovae, blacknose Carcharhinus acronotus, and blacktip C. limbatus sharks. Blacknose sharks had the highest catch per unit effort (CPUE) in the middepth stratum (10–30 m), blacktip sharks had consistently higher CPUE in the shallow depth stratum (<10 m), and Atlantic sharpnose sharks showed high abundance throughout both the shallow and middepth strata. Length frequency and sex ratio analyses suggest that Atlantic sharpnose and blacknose sharks are using waters greater than 30 m deep for parturition, whereas adult blacktip sharks are probably using shallow waters for parturition. Our abundance patterns illustrate a continuum of depth use across the inner continental shelf. Surveys that do not encompass the entirety of this ecosystem fail to accurately characterize the distributions of these important predators.

Potential Sources of Survey Bias Associated with Hand‐Retrieved Longline Catches of Subadult Sharks in Georgia Estuaries

AbstractLunar phase, tide stage, and bait type were examined as potential sources of survey bias affecting catch rates of subadult sharks on hand‐retrieved longlines in Georgia estuaries. Sampling occurred during April–September from 2001 to 2003 in eight of Georgia's nine estuaries; this sampling period coincides with the pupping seasons for a variety of shark species. The effects of lunar phase and tide stage on catch rates of sharks were evaluated during 2001 and 2002. The effect of bait type (i.e., squid Loligo spp. or spot Leiostomus xanthurus) on shark catch rates was evaluated during 2003. During 2001 and 2002, 420 subadult sharks representing two families (Carcharhinidae and Sphyrnidae) and nine species were caught during 212 longline sets. Catch rates were evaluated for the four most commonly occurring shark species: the Atlantic sharpnose shark Rhizoprionodon terraenovae, bonnethead Sphyrna tiburo, blacktip shark Carcharhinus limbatus, and sandbar shark C. plumbeus. Neither lunar phase nor tide stage affected catch rates of any species other than blacktip sharks. In 2003, longline sets (n = 80) resulted in the capture of 177 subadult sharks from seven species. Overall catch rates were higher with squid bait than with spot, and bait type also affected shark species catch composition. Mean sizes of Atlantic sharpnose sharks were significantly different between the two bait types, indicating a possible ontogenetic shift in bait preference. For example, catch of neonate Atlantic sharpnose sharks was higher on hooks baited with squid than on hooks baited with spot, whereas catch of juveniles was higher on hooks baited with spot. Although timing of sampling events did not influence catch rates of subadult sharks, bait choice could bias estimates of abundance for certain life stages and affect the probability of detecting some species.

Isolation and properties of acid- and pepsin-soluble collagen from the skin of blacktip shark (Carcharhinus limbatus)

Acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) from the skin of blacktip shark (Carcharhinus limbatus) were isolated and characterized. The yield of ASC (20.01%) was much higher than that of PSC isolated from the residue of ASC extraction (0.86%). Both collagens had protein as their major constituent with the trace amounts of ash and fat. Based on protein patterns and TOYOPEARL® CM-650M column chromatography, both collagens contained α- and β-chains as their main components and were characterized as type I collagen with the cross-link of α2-chain. Similar peptide maps of both collagens, digested by either V8 protease or lysyl endopeptidase, were observed but they were totally different from those of type I collagen from calf skin hydrolyzed by the same enzyme. Thermal transition temperature (T max) of ASC and PSC were 34.23 and 34.37 °C, respectively. Fourier-transform infrared spectra suggested that both collagens were in triple-helical structure. From zeta potential analysis, isoelectric points (pI) of ASC and PSC were estimated to be 6.78 and 7.02, respectively. Thus, blacktip shark skin may serve as an alternative source of collagen and acid solubilization process could be implemented with ease and high yield.

Determining shark size from forensic analysis of bite damage

Bite damage patterns have long been used to estimate shark species and body size, with somewhat limited success. The lack of fit between damage patterns and shark size is partially due to variation in tooth size and shape within an individual. The ability to accurately predict body size from bite patterns is important for better understanding the ecological and behavioral underpinnings of shark bites/attacks on marine organisms, humans, and submarine equipment. To this end, we measured interdental distance (IDD) between the most labial teeth in the first six tooth files on both the upper and lower jaws, as well as the circumference of the portion of each jaw that bears teeth, for prepared jaw sets from fourteen shark species and regressed these data against total length. IDD is allometric as well as an accurate predictor of total length in all species examined, except Carcharhinus acronotus. Tooth-bearing circumference is also allometric and predictive of total length in all species. Though considerable overlap exists in IDD and circumference ranges among species for the total length ranges examined, Carcharodon carcharias and Isurus sp. can be differentiated from Carcharhinus limbatus, Carcharhinus brevipinna, and C. acronotus based on these values alone. When combined with knowledge of species-specific feeding behavior, geographic distribution, and habitat preferences, these simple measures from bite damage patterns allow quick, accurate assessment of shark size and potential species.

Biological aspects of sharks caught off the Coast of Pernambuco, Northeast Brazil

One hundred seventeen specimens of sharks were caught along the coast of Pernambuco State, Northern Brazil, between May 2004 and May 2007, among which 86 were blacknose sharks, Carcharhinus acronotus, enabling a more detailed study of the species. Blacknose sharks were caught in the 2 study areas along the Boa Viagem/Piedade and Paiva beaches, accounting for the highest relative abundance among the species caught (73.5% of total). Potentially dangerous sharks, tiger and bull sharks, were also caught in the same areas, whereas hammerhead and blacktip sharks were only captured off Boa Viagem/Piedade. Concerning the blacknose shark, the total length (TL) ranged from 39.0 to 180.0 cm. Among the 38 females analysed, 32 were juveniles, 11 were maturing, 2 were pre-ovulatory and 21 were pregnant. Sexing was possible for 75 of the 83 embryos, 38 of which were males and 37 were females, with a sex proportion of 1:0.9 and total length ranging between 6.4 and 63.5 cm. Ovarian fecundity ranged from 5 to 10 and uterine fecundity from 1 to 3, with an estimated gestational period of 9 months. Among the 48 males, 6 were juveniles and 42 were adults. Both males and females seem to reach sexual maturity at about 105.0 cm TL. Among the 86 stomachs analysed, only 22.1% had contents, with teleosts as the most frequent item.

Capture time, size and hooking mortality of bottom longline-caught sharks

The primary gear type used to harvest coastal sharks in the U.S. Atlantic shark fishery is bottom longline. Recent stock assessments have found several species of coastal sharks in U.S. Atlantic Ocean waters have declined from 60% to 80% of virgin levels. To aid in stock rebuilding, alternative gear restriction measures such as reduced soak time, restrictions on the length of gear, and fishing depth restrictions have been considered but not implemented. In order to evaluate the effectiveness of some of these management measures, controlled experiments were performed using hook timers and time depth recorders, assessing the factors affecting mortality during longline capture for the four most abundant species that incurred at-vessel mortality: sandbar ( Carcharhinus plumbeus), blacktip ( Carcharhinus limbatus), bull ( Carcharhinus leucas), and blacknose ( Carcharhinus acronotus). Our results indicate that as hook time and shark size increased mortality rates for the sandbar and blacktip sharks increased. Predicted models indicated mortality rates increased steadily for the three species but appeared to increase the most after 10, 6, and 1 h on the hook for sandbar, blacktip and blacknose shark, respectively. Sandbar sharks larger than approximately 170 cm FL are more susceptible to hooking mortality. Blacknose shark mortality rates increased as hook time increased but bull shark mortality rates were not affected by any factor. The probability of a hook being bitten increased the most between 5 and 12 h after the fishing gear had been set and the mean amount of time hooks were in the water prior to being bitten was 4, 5 and 9 h for sandbar and blacknose sharks, blacktip, and bull sharks, respectively. A significant difference was found between these means for sandbar and bull sharks and between blacknose and bull sharks. Shark species were commonly caught at different temperature and depth ranges. These results could be used by fisheries management to implement restrictions of fishing depth and soak time to aid in the recovery of coastal sharks species.

Comparative study on characteristics of gelatin from the skins of brownbanded bamboo shark and blacktip shark as affected by extraction conditions

Gelatins from the skins of brownbanded bamboo shark (BBS; Chiloscyllium punctatum) and blacktip shark (BTS; Carcharhinus limbatus) were extracted using the distilled water at different temperatures (45, 60 and 75 °C) and times (6 and 12 h). Yields of gelatin from the skins of BBS and BTS were 19.06–22.81% and 21.17–24.76% (based on wet weight), respectively. Gelatins from both species extracted at 45 °C for 6 h exhibited the highest bloom strength (206–214 g), which was higher than that of commercial bovine bone gelatin (197 g) ( p < 0.05). Gelatin gels from BBS skin could set at room temperature (25–26 °C) within 24 min. However, gelatin gels from BTS skin was not able to set within 3 h at the same temperature. Scanning electron microscopic study showed that gelatin gel from BBS skin presented the thicker strand than those from BTS skin and bovine bone. Cross-linked components (β- and γ-chains) and α-chains were more degraded with increasing extraction temperatures, especially at 75 °C. Gelatin from BTS skin was more susceptible to hydrolysis than that from BBS skin. Fourier transform infrared (FTIR) study revealed that the major absorption bands of gelatin from the skins of both sharks shifted to a higher wavenumber, compared with their corresponding acid soluble collagen (ASC). Therefore, gelatins from the skin of BBS has a potential to replace mammalian for gelatin, due to its similarity in bloom strength and setting behavior to the commercial bovine bone gelatin.

Bycatch mitigation assessment for sharks caught in coastal anchored gillnets

Fishing with modified gillnets was conducted to elucidate their potential for reducing shark bycatch. Experimental fishing focused on two commercial fisheries, Spanish mackerel ( Scomberomorus maculatus) and spot ( Leiostomus xanthurus). The modification took the form of increasing the gillnet tension using larger floats on the head-rope and increasing the lead-core lead-line weight. Gillnet mesh sizes were 7.2 cm (spot fishery) and 7.6 and 10.2 cm (Spanish mackerel fishery). Gillnet selectivity of the four most commonly encountered shark species were fitted to fork-length distribution data using the SELECT method. There was no significant difference in the catch rate of the target species between control and modified gillnets for all mesh sizes used. Catch rates of some shark species were significantly reduced in modified gillnets. Model deviance values indicated good fits to the data for blacknose ( Carcharhinus acronotus), blacktip ( Carcharhinus limbatus) and bonnethead ( Sphyrna tiburo) sharks with lowest deviance values (i.e., best fit) generally associated with the normal scale (spread proportional to mesh size) form. The selectivity results demonstrated that all life stages of Atlantic sharpnose ( Rhizoprionodon terraenovae) and blacknose sharks were available to the gillnets. The mesh selectivity of bonnethead sharks was largely uniform due to their exaggerated cepholaphoil that resulted in the majority being hammer-wrapped. Further, capture data indicated a dominance of large juveniles and adult bonnethead sharks resulting in poor model fits. The capture mortality rate for all shark species was high (78.6%) with higher mortality rates associated with heightened locomotor performance and wrapping as an entanglement mode. These results demonstrated that modified gillnets have the potential to reduce shark bycatch, particularly for those species for which wrapping was the primary entanglement mode.

Temporal variation in the artisanal elasmobranch fishery of Sonora, Mexico

Baseline, species-specific information is largely unavailable for artisanal elasmobranch fisheries, but is essential for the monitoring of exploited populations and the development of effective management plans. Seasonal surveys were conducted during 1998–1999 in Sonora, Mexico to determine the extent and activities of artisanal elasmobranch fisheries operating in the eastern Gulf of California. Nineteen fishing sites were documented, the majority of which (84.2%) targeted elasmobranchs during some part of the year. Most small demersal sharks and rays were landed in bottom set gillnet fisheries that also targeted demersal teleosts, whereas large sharks were usually taken in directed surface longline or, to a lesser extent, drift gillnet fisheries. Rays numerically dominated sampled landings in Sonora (63.4%, n = 100,136), and catch rates exceeded those of sharks during spring and summer months. The shovelnose guitarfish, Rhinobatos productus, was the primary fishery target during these seasons. During autumn, small sharks, especially mustelids ( Mustelus spp.) were numerically dominant, but rays (e.g., Dasyatis dipterura) were also caught in large numbers. Winter landings in Sonora were principally composed of mustelid sharks, which represented the greatest seasonal catch rates of all elasmobranch taxa during this study. Large sharks were of comparably minor importance, with a limited summer fishery operating in the southern part of the state. Variation in catch composition was evident in association with differential interannual environmental conditions (El Niño and La Niña) and seasonal temperature fluctuations. Size composition of landings varied greatly by species, but relatively small size classes of sharks and rays were abundant and large, often gravid females of several ray species (e.g., R. productus and Narcine entemedor) supported spring and summer fisheries in nearshore waters. Populations of many large shark species (e.g., Carcharhinus leucas, Carcharhinus limbatus, Carcharhinus obscurus and Galeocerdo cuvier) have likely been overfished, prompting a shift in effort towards coastal populations of smaller elasmobranchs.

FAUNA DE ELASMOBRÂNQUOS DO ESTUÁRIO DO RIO CURU, CEARÁ, BRASIL

Os estuários possuem relevante interatividade ecológica com ecossistemas vizinhos, sendo habitat de relativamente elevada diversidade de espécies. Poucos são os estudos que citam a ocorrência de elasmobrânquios nos estuários do Ceará. O objetivo principal deste trabalho foi caracterizar a fauna de elasmobrânquios do estuário do rio Curu. Entre setembro de 2004 e dezembro de 2007, pescarias artesanais realizadas no estuário foram mensalmente monitoradas. Foi registrada a ocorrência de seis espécies: Rhizoprionodon porosus (n=4), Carcharhinus limbatus (n=2),Dasyatis guttata (n=130), D. marianae (n=6),Gymnura micrura (n=8) e Aetobatus narinari(relato etnoecológico). A partir destes resultados, o número de espécies de elasmobrânquios registradas para o estuário do rio Curu triplicou (de duas para seis espécies), sendo que para os estuários do Estado, aumentou em 50% (de seis para nove espécies). A quase totalidade dos animais coletados correspondia a neonatos. O estuário do rio Curu atende pelo menos parcialmente a um dos três critérios que definem uma área de berçário. A confirmação desse status depende de pesquisas adicionais.

Parthenogenesis in a large‐bodied requiem shark, the blacktip Carcharhinus limbatus

Genetic evidence is provided for parthenogenesis in a large‐bodied shark, the blacktip Carcharhinus limbatus, from the speciose and commercially important family Carcharhinidae, the first verified case of asexual development in this lineage and only the second for any chondrichthyan. The parthenogenetic embryo exhibited elevated homozygosity relative to its mother, indicating that automictic parthenogenesis is the most likely mechanism. Although this finding shows that parthenogenesis is more common and widespread in sharks than previously realized and supports the early existence of parthenogenetic abilities in vertebrates, the adaptive significance of automixis in these ancient fishes remains unclear.

Feeding ecology and growth of neonate and juvenile blacktip sharks Carcharhinus limbatus in the Timbalier–Terrebone Bay complex, LA, U.S.A.

Stomach contents and vertebrae from neonate and juvenile blacktip sharks Carcharhinus limbatus (n= 334) were examined to describe their diet, feeding patterns and growth within the Timbalier–Terrebone Bay complex, LA, U.S.A. In the study area, both neonate and juvenile C. limbatus feed primarily on gulf menhaden Brevoortia patronus. However, based on the index of relative importance (IRI), gulf menhaden constituted a larger portion of the diet of neonates (84·05 %IRI) than for juveniles (47·91 %IRI). An increase in the index of relative fullness between the afternoon and dusk time intervals and a large decrease in the percentage of empty stomachs between the night and early morning time intervals suggested that these fish exhibited a diel feeding pattern with crepuscular periods being the times of highest feeding activity. A higher percentage of empty stomachs (neonates 68% and juveniles 39%) and a significantly lower growth rate (age 0+ year C. limbatus, 0·62 mm day−1; age 1+ year fish, 0·89 mm day−1) could indicate that neonate C. limbatus are less efficient predators than older conspecifics.

Presencia de juveniles de tiburón aletinegro Carcharhinus limbatus (Carcharhiniformes: Carcharhinidae) en la zona norte de la ecoregión Tayrona, Caribe colombiano

The presence of two young Carcharhinus limbatus (Valenciennes, 1839) is documented. The individuals were collected by artisanal fishers in the area around th...

First characterization of shark nursery habitat in the United States Virgin Islands: evidence of habitat partitioning by two shark species

Little is known of the diversity, demography, and essential fish habitat of sharks within the United States Virgin Islands (USVI) marine ecosystem. To examine species diversity and the relative abundance of elasmobranchs in this region, bottom-longline and hand-gear sampling was conducted in Fish Bay, St. John, USVI, from June 2004 to December 2005. In the 8 sampling trips during this period, 54 standardized longline sets caught 174 elasmobranchs comprising 5 species of sharks and 1 batoid. Overall catch per unit effort [ln(CPUE + 1) ± SE] was 1.83 ± 0.16 elasmobranchs 100 hooks–1 h–1. Lemon sharks Negaprion brevirostris had the highest relative abundance based on log-transformed CPUE data (0.98 ± 0.15), followed by blacktip sharks Carcharhinus limbatus (0.91 ± 0.18), southern stingrays Dasyatis americana (0.28 ± 0.08), nurse sharks Ginglymostoma cirratum (0.08 ± 0.05), blacknose sharks Carcharhinus acronotus (0.06 ± 0.04) and the Caribbean sharpnose Rhizoprionodon porosus (0.03 ± 0.03). The relative abundance of all species was significantly higher in the summer (2.6 ± 0.2) than during the winter (1.1 ± 0.2). For the blacktip (N = 89 captures of 74 individuals) and lemon (N = 66, 48 individuals) sharks, which comprised the bulk of the catch, mean fork length (± SE) was 51.9 ± 0.63 cm and 59.9 ± 1.2 cm, respectively, representing primarily neonatal and young-of-the-year life stages. The recapture rates for blacktip and lemon sharks were 21% and 29%, respectively, and nearly all recaptures occurred within the bay, indicating a high degree of site fidelity. Capture information and limited acoustic tracking provided evidence of spatial and temporal habitat partitioning by these 2 shark species within the bay. Although the CPUE of both species was highest over shallow (<1 m) seagrass substrate, lemon sharks were found and tracked exclusively on shallow, mangrove-fringed seagrass habitat, while blacktip sharks utilized a wider area of the bay. Fish Bay was determined to provide important nursery habitat for young juvenile lemon and blacktip sharks in the USVI.

Shark Attacks in Dakar and the Cap Vert Peninsula, Senegal: Low Incidence despite High Occurrence of Potentially Dangerous Species

BackgroundThe International Shark Attack File mentions only four unprovoked shark attacks on the coast of West Africa during the period 1828–2004, an area where high concentrations of sharks and 17 species potentially dangerous to man have been observed. To investigate if the frequency of shark attacks could be really low and not just under-reported and whether there are potentially sharks that might attack in the area, a study was carried out in Dakar and the Cap Vert peninsula, Senegal.Methodology/Principal FindingsPersonnel of health facilities, administrative services, traditional authorities and groups of fishermen from the region of Dakar were interviewed about the occurrence of shark attacks, and visual censuses were conducted along the coastline to investigate shark communities associated with the coasts of Dakar and the Cap Vert peninsula. Six attacks were documented for the period 1947–2005, including two fatal ones attributed to the tiger shark Galeocerdo cuvieri. All attacks concerned fishermen and only one occurred after 1970. Sharks were observed year round along the coastline in waters 3–15 m depth. Two species potentially dangerous for man, the nurse shark Ginglymostoma cirratum and the blacktip shark Carcharhinus limbatus, represented together 94% of 1,071 sharks enumerated during 1,459 hours of observations. Threatening behaviour from sharks was noted in 12 encounters (1.1%), including 8 encounters with C. limbatus, one with Galeocerdo cuvieri and 3 with unidentified sharks.Conclusions/SignificanceThese findings suggest that the frequency of shark attacks on the coast of West Africa is underestimated. However, they also indicate that the risk is very low despite the abundance of sharks. In Dakar area, most encounters along the coastline with potentially dangerous species do not result in an attack. Compared to other causes of water related deaths, the incidence of shark attack appears negligible, at least one thousand fold lower.

Occurrence, Diet and Growth of Juvenile Blacktip Sharks,Carcharhinus limbatus, from Los Roques Archipelago National Park, Venezuela

Abstract. Distribution, occurrence, diet and growth of juvenile blacktip sharks, Carcharhinus limbatus, were examined based on specimens caught between 1995 and 2002 by the artisanal shark fishery from Los Roques Archipelago. Fishery monitoring revealed that C. limbatus was the species most frequently caught, accounting for 48.5% of the shark catch. Capture of neonate and juvenile sharks was concentrated in the central lagoon of the archipelago, indicating that this area corresponds to a nursery area for the species. Birth season was approximately from mid June to the end of August. Average length at birth was 63.5 cm TL, based on neonates with an open umbilical scar. The smallest mature male and female sharks measured 152 and 161 cm TL, respectively. Diet was composed of teleost fishes, with the most important prey being Eucinostomus argenteus (13.3 %IRI), Opisthonema oglinum (6.9 %IRI) and Gerres cinereus (5.5 %IRI). Monthly length frequencies revealed that juveniles remain within the nursery area for 1...