The sicklefin lemon shark Negaprion acutidens is a large-bodied (> 3m) coastal shark species, widely distributed in tropical and sub-tropical Indo-Pacific waters. Despite its large size and wide distribution, very little is known about its movement behaviour throughout ontogeny. The primary aim of this thesis was to gain an understanding of the movements of sub-adult N. acutidens, in and around the St. Joseph Atoll, Republic of Seychelles, to facilitate the effective conservation of this vulnerable species. A total of 22 sharks (139 – 202 cm TL) were equipped with coded acoustic transmitters and passively monitored using moored acoustic receivers for a period of 20 month from March 2009 to October 2010. The use of passive acoustic telemetry arrays to study behavioural ecology has increased in popularity in recent years and been successfully applied to study a host of teleost and elasmobranch species in a diversity of habitats, ranging from sheltered estuaries to the offshore pelagic environment. However, the practicalities of designing an effective network of receivers to optimally monitor animal movements can be challenging. In this study the receiver array was optimised through a series of incremental steps to achieve an efficient design that allowed for the specific objectives to be addressed. The specific objectives of this study were to i) gain an understanding of the long term space use patterns and site fidelity of sub-adult N. acutidens within degree of use of the St. Joseph Atoll lagoon and surrounding habitats, and ii) investigate their short term behavioural patterns in response to natural rhythmic cycles. The important role the atoll plays in the sub-adult stage of this species was demonstrated by the very low numbers of detections outside the atoll compared to the very large numbers of detections inside the atoll. Over the course of a year the tagged sharks showed a high degree of site fidelity to the atoll, with 79 – 100% of the individuals detected during each month and 50% being detected on a near daily basis. This result provides testimony of the nursery role of the atoll and importance of these habitats in the early life history for this species. Individual area use was generally found to be restricted to the eastern part of the atoll incorporating a portion of the central deep lagoon and a nearby adjacent area of the sand flats. The movements of sub-adult N. acutidens on and off of the shallow flats surrounding the central lagoon (likely for foraging) were found to be strongly influenced by the tidal height and the diel cycle. Tagged sharks were found to utilise the flats more regularly when the tidal height was greater than 90 cm and particularly more so during the night and early morning than during daylight times. The combined results of this study expose the vulnerability of this species to rapid local depletion. Similarly, the effectiveness of spatial management measures, such as no-take marine protected areas is highlighted as an efficient tool for the future conservation of this species. In the St. Joseph Atoll in particular, the use of a multi-levelled protection approach, where the eastern portion on the atoll is completely restricted while the remaining area is utilized for non-consumptive tourism activities, could be highly effective. Future research should investigate changes in area use throughout the ontogeny of this species as well improve the understanding of the breeding site fidelity and population size of reproductive females using the St. Joseph Atoll.

The silky shark Carcharhinus falciformis forms the primary elasmobranch bycatch in tuna purse seine fisheries using fish aggregating devices (FADs) in all of the world’s tropical oceans. Its life-history traits of slow growth, late maturation and low fecundity make it vulnerable to over exploitation, as is apparent from historical bycatch trends. Very little is known about the associative behaviour of this species with floating objects, information which is essential in formulating effective mitigation and management measures. This study aims to address this knowledge gap through the use of various electronic tagging techniques in conjunction with dietary analysis. Dietary data were collected from 323 silky sharks incidentally caught at FADs. Approximately 40 percent of the diet consisted of prey associated with FADs while the remaining 60 percent were non-associated species of crustaceans, cephalopods and fishes. These results suggest that the associative behaviour is not primarily driven by trophic enhancement, but is likely a combination of predator avoidance, social interactions and feeding. Fine-scale behavioural data from silky sharks associated with drifting FADs were collected through the use of acoustic telemetry techniques. Acoustic tags were implanted into 38 silky sharks (69- 116 cm TL) at eight FADs. FADs were equipped with satellite linked acoustic receivers and abandoned to drift freely. Presence/absence and swimming depth data were telemetered via the Iridium satellite system. A total of 300 d of behavioural data were collected from 20 tagged individuals. Individuals remain associated with the same FAD for extended periods (min = 2.84 d, max = 30.60 d, mean = 15.69 d). Strong diel patterns were observed in both association and swimming depth. Typically individuals moved away from FADs after sunset and return later during the night, then remain closely associated until the following evening. Vertical behaviour also changed around sunset with sharks using fairly constant depths, within the upper 25 m, during the day and switching to rapid vertical movements during the night, with dives in excess of 250 m recoded. Broader scale movement behaviour was investigated using pop-up archival satellite tags (PSATs). Tags were deployed on 46 silky sharks (86-224.5 cm TL) for a total of 1495 d. Light data were used to calculate geolocation estimates and reconstruct the sharks’ trajectories. Movement patterns differed between animals and according to deployment duration. Several extensive horizontal movements were observed, with an average track length of 3240 km during an average tag deployment of 44.02 d. Horizontal movement patterns were found to correlate very closely with drift patterns of FADs. Consequently, it appears that the movement behaviour of juvenile silky sharks is strongly influenced by the movement of drifting FADs in this region. Ghost fishing of silky sharks through entanglement in FADs was also investigated using data derived from PSATs as well as underwater visual censuses. Thirteen per cent of the tagged sharks became entangled in FADs and entangled sharks were observed in 35 percent of the 51 FADs surveyed. Using this information in conjunction with estimated time that sharks remained entangled in the FAD (from depth data from PSATs), and scaling up according to estimates of FAD numbers, it was found that between 480 000 and 960 000 silky sharks are killed annually in this manner in the Indian Ocean. Subsequent management measures in this region prevent the deployment of FADs with netting that could lead to entanglement. Overall, floating objects appear to play a significant role in the juvenile life stages of silky sharks in this region. While their association with floating objects is clearly advantageous in an evolutionary sense, under current tuna fishery trends, this behaviour is certainly detrimental for the population.

The blacknose shark (Carcharhinus acronotus) is a common small coastal shark species found in nearshore waters along the southeast coast of the United States, from North Carolina into the Gulf of Mexico and extending further south into the Bahamas. There has been some debate in recent years over the reproductive periodicity of C. acronotus in waters off the U.S. coast. Earlier studies have suggested that Gulf C. acronotus reproduce on an annual basis whereas the Atlantic populations of this species may reproduce biennially. Additionally, there have been no known studies on the diet of C. acronotus. The goal of the present study was to re-evaluate the reproductive biology of the Atlantic populations of C. acronotus with the intent on clarifying discrepancies in reproduction as well as provide information on dietary trends. This was accomplished by examining male and female reproductive tracts and gut contents in animals caught throughout the Atlantic range of C. acronotus. Based on these data, spermatogenesis occurs between late May to early July with peak sperm production occurring in June and July. In females, follicular development is complete by late June-early July with ovulation occurring shortly afterwards. Mating occurs between mid-June and early July based on the presence of fresh mating scars on females captured during this time. Current data suggests that gestation begins late July with parturition occurring late May to early June the following year. As observed in earlier studies, reproductive periodicity appears to be largely biennial. However, evidence for concurrent follicular development and pregnancy was observed in several females, suggesting that at least a portion of the Atlantic population may reproduce on an annual basis. Dietary data shows a dominance of teleost prey items in the diets of C. acronotus with scianids making up the majority of the identifiable teleosts.

Submitted by (edna.saturno@ufrpe.br) on 2017-02-14T16:23:03Z No. of bitstreams: 1 Jones Santander Neto.pdf: 1353954 bytes, checksum: 3ab25dad19a919fb57b060eb783f2097 (MD5) / Made available in DSpace on 2017-02-14T16:23:03Z (GMT). No. of bitstreams: 1 Jones Santander Neto.pdf: 1353954 bytes, checksum: 3ab25dad19a919fb57b060eb783f2097 (MD5) Previous issue date: 2011-07-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / From October 2007 to March 2011, 105 silky sharks, Carcharhinus falciformis (Muller e Henle, 1839), (68–274.2 cm in total length, TL) were collected from industrial fleet (longline) carried out on Southwestern Tropical Atlantic (010º W/ 035º W, 05º N/ 30º S). Vertebral sections from 34 males (105–268.2 cm TL), 35 females (85–274.2 cm TL), and 36 individuals of unknown sex (68.8-256.1 cm TL) were analyzed. One 68.8 cm TL individual did not have birth ring. The index of average percentage of error (IAPE) estimated from two readings ranged from 0 to 7.69 (mean=3.88%) in the vertebrae of specimens with 1 and 14 band pairs, respectively. There were no differences (p 0.05) in the monthly marginal increment (MIR) analysis between months then we considered an annual ring deposition as other species of the Carcharhinidae family, including Carcharhinus falciformis. Ages range from 0 to 20 years. There were no differences (p 0.05) in growth between sexes. Models derived from von Bertalanffy, particularly the VBGM two phase, best represented growth for the species, which was evidenced by the lowest Akaike information criterion value. Growth parameters estimated for both sexes were L = 303 cm, k = 0.086, t0= -4.71, h=0.17, and th=11.62 with the VBGM two phase model, and L = 292 cm, k = 0.089, and t0= -4.87 with the VBGM. The VBGM was used to other analysis. Males and females mature at 10.8 and 12.5 years of age, repectively, and the age that attain 95% of the L is 30.3 years. / Tubarões lombo preto, Carcharhinus falciformis (Muller e Henle, 1839) foram capturados entre outubro de 2007 a março de 2011 pela frota industrial atuando com espinhel pelágico no Atlântico sudoeste Tropical (010º W/ 035º W, 05º N/ 30º S). Foram coletadas vértebras de 105 exemplares, sendo 34 machos (105–268,2 cm CT), 35 fêmeas (85–274,2 cm CT) e 36 indivíduos de sexo não identificado (68,8-256,1 cm CT). Um indivíduo em vida livre medindo 68,8 cm CT não apresentou marca de nascimento. O índice de porcentagem de erro médio (IAPE) estimado entre dois leitores variou de 0% a 7,69% (média= 3,88%) nas vértebras de espécimens com 1 e 14 pares de bandas, respectivamente. Ao analisar o incremento marginal relativo (IMR) não se verificou diferenças (p 0,05) entre os meses, logo assumiu-se a deposição de um anel anual como utilizado para as demais espécies da família Carcharhinidae, inclusive C. falciformis. Idades variaram de 0 a 20 anos. Não houve diferenças (p 0,05) no crescimento entre os sexos. Modelos derivados de von Bertalanffy, particularmente VBGM duas fases, melhor representou o crescimento para a espécie, que foi evidenciado pelo menor valor do critério de informação de Akaike. Parâmetros de crescimento estimado foram L = 303 cm, k = 0,086, t0= 4,71, h=0,17 e th=11,62 com o VBGM duas fases e L = 292 cm, k = 0,089, and t0= -4,87 com o VBGM. O VBGM foi utilizado para as demais análises. Machos e fêmeas maturam com 10,8 e 12,5 anos, respectivamente e a idade com que atingem 95% do L é 30,3 anos.