Thesis (M. Phil.)--University of Hong Kong, 2010. / Includes bibliographical references (p. 185-208). Also available in print.

The bull shark, Carcharhinus leucas, is an important euryhaline predator that is exploited throughout its range for meat and fins. This species is taxonomically paired with the pigeye shark, C. amboinensis. Validity of this group has not been directly tested using molecular markers. Genetic variation and phylogeny was examined with concatenated datasets of mitochondrial genes (cytb, cox1 and 12stRNA16s) for nineteen species, from three families within the order Carcharhiniformes. Whilst there were indications of species pairings within the genus, there was no evidence to suggest that the bull and pigeye sharks should be considered a species group. Phylogenetic analysis failed to resolve Carcharhinus, but confirmed Negaprion as a sister taxon and placed Prionace glauca within Carcharhinus. It remains unclear if the family Sphyrnidae, arose from a Rhizoprionodon or Scoliodon ancestor and future revision of this complex group of sharks is required. Like other large carcharhinid species, C. leucas exhibits a low reproductive rate and long generation times. It is susceptible to localised depletions and such declines have been documented. The global stock structure was assessed by analysing the mitochondrial control region in 245 individuals sampled from eight populations in three ocean basins. The bull shark exhibits relatively high haplotype diversity (0.896 ± 0.010) when compared to other globally-distributed sharks and the nucleotide diversity was similar to others from the genus (0.00465 ± 0.00014). There was significant stock structure found among populations (ΦST=0.736, p<0.00001) and among ocean basins (ΦCT=0.527, p=0.00653). Geneflow between the US Atlantic coastline and Gulf of Mexico was sufficient to consider the area to be a single panmictic population. Coalescent analyses suggest an Indian Ocean origin with population divergences associated with warm interglacials and increased habitat with drop in sea level during the recent Wisconsin glaciation. Seven discrete stock management units for bull sharks are proposed.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

Contrairement au requin mako, l´évolution des débarquements de requins peau bleue en Atlantique nord-est a connu une augmentation durant les deux années 2012 et 2013. Les requins vendus à la criée sont majoritairement juvéniles, l´âge de maturité étant tardif chez les deux espèces. Les stratégies alimentaires du peau bleue et du mako ont été étudiées par des analyses des contenus stomacaux associés aux isotopes stables. Le large spectre de proies identifiées confirme le caractère généraliste et opportuniste de leur alimentation. Les résultats indiquent que les céphalopodes sont les proies principales du requin peau bleue et que les téléostéens, en particulier le balaou de l´Atlantique (Scomberesox saurus), sont les principales proies du requin mako. Leur place de prédateurs supérieurs dans l´écosystème marin pélagique a été confirmée par leur niveau trophique à partir, 1) des contenus stomacaux : 4,8 pour le requin bleue et à 5,0 pour le requin mako, et 2) des ratios isotopiques : 5,2 et 5,3 respectivement. Les signatures isotopiques ont montré certaines incohérences en terme de fractionnement entre les requins et leurs principales proies qui peuvent s´expliquer par le caractère opportuniste et migratoire des requins mais également par leur métabolisme. Les teneurs en mercure total (Hg) observées dans la chair consommée des requins peau bleue et requin mako sont, en moyenne, en dessous du seuil limite autorisé par l´Union Européenne (1 mg/kg de chair fraîche). Cependant, les grands individus accumulent des quantités élevées, les requins peau bleue de plus de 248 cm et les requins mako de plus de 178 cm s´avérant majoritairement impropres à la consommation. / Over the past two years, landings of mako have decreased and those of blue shark increased. The sharks landed in a fish market are mainly juvenile, the maturity age being late for both species. Feeding strategies were studied for blue shark and shortfin mako on the basis of stomach content and stable isotope analyses. The high number of identified prey species confirms these sharks’generalist and opportunistic diet. Results showed that cephalopods were the main prey for blue shark, while teleosts, especially Atlantic saury (Scomberesox saurus), were the main prey for shortfin mako. Their top-predator status in the marine pelagic ecosystem was confirmed by their estimated trophic levels from 1) stomach content analyses: 4.8 for blue shark and 5.0 for shortfin mako, and 2) stable isotope ratios: 5.2 and 5.3 respectively. The stable isotope ratios showed some incoherence in fractioning between sharks and their prey. This may be explained by their opportunistic diet and the migratory behaviour of shark, associated with their metabolism. The mercury mean level in the muscle of blue shark and shortfin mako was below the maximum limit allowed by the European Union (1mg/kg fresh meat). However, large sharks showed higher mercury levels. Shark meat was considered unfit for human consumption for blue shark bigger than 248 cm and for shortfin mako bigger than 178 cm. Some tests were undertaken under real longline fishing conditions to investigate ways to reduce shark catches. The results showed that electromagnetic waves were ineffective to reduce catches of blue shark.

Submitted by (edna.saturno@ufrpe.br) on 2017-02-13T12:40:28Z No. of bitstreams: 1 Fernanda de Oliveira Lana.pdf: 2191655 bytes, checksum: 1c0fe338043dce8d998d515ebec30b36 (MD5) / Made available in DSpace on 2017-02-13T12:40:28Z (GMT). No. of bitstreams: 1 Fernanda de Oliveira Lana.pdf: 2191655 bytes, checksum: 1c0fe338043dce8d998d515ebec30b36 (MD5) Previous issue date: 2012-02-13 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / The silky shark, Carcharhinus falciformis, is an abundant species in tropical and equatorial waters of the pelagic zone. The present work aimed at studying the ecology of the silky shark, including aspects of its reproduction, relative abundance, distribution, habitat use and migration on the Equatorial Atlantic Ocean. From November 1992 to December 2011, 153 specimens were examined, 72 males and 81 females, resulting in a sex ratio close to 1:1 (0.89:1.00). All specimens were caught by commercial tuna longline boats, in the area located between 08°N to 53°S latitude and 08°E to 48°W longitude. The results suggest a size at first maturity for females around 205- 210 cm and for males between 180- 200 cm TL. Females were found in 5 maturational stages: juvenile (n = 29/ 35.8% from 74 to 204 cm, TL), maturing (n = 10 / 12.3%, from 215 to 295 cm TL), pre- ovulatory (n = 14 / 17.3%, 177 to 280 cm TL), pregnant (n = 24 / 29.6%, 203 to 270 cm TL) and resting (n = 4 / 4.9%, from 223 to 285 cm TL). Males were classified into 4 stages: juvenile (n = 38/ 52.8% from 81 to 220 cm TL and clasper length - CL <12 cm), maturing (n = 16/ 22.2%, from 166 to 208 TL cm, 9.5 to 24.5 cm CL;), adult (n = 17/ 23.6%, from 141 to 272 cm TL, CL> 24.5 cm) and neonate (n = 1/ 1.4%, 82 cm TL, CL 4 cm). Catch and effort data from 16.016 sets made by Brazilian tuna longliners, from 2004 to 2011, were analyzed. The CPUE was calculated and the catch and effort data were grouped in squares of 5° x 5° latitude and longitude. Two silky sharks were tagged with satellite transmitters PSAT (Pop-up Satellite Archival Tag), in the vicinity of Archipelago of Saint Peter and Saint Paul – ASPSP, but from only one it was possible to recover the data. The preferred temperature range of the tagged animal was between 27 and 28°C with a preferred depth between 1 and 10m. / O tubarão lombo-preto, Carcharhinus falciformis, é uma espécie abundante na zona pelágica, com distribuição em águas tropicais e equatoriais de todos os oceanos do mundo. O presente trabalho teve por objetivo estudar a ecologia do tubarão lombo-preto, incluindo aspectos da sua reprodução, abundância relativa, distribuição, uso do habitat e padrões de migração, na margem ocidental do Oceano Atlântico Equatorial. No período de novembro de 1992 a dezembro de 2011, foram examinados 153 exemplares, 72 machos e 81 fêmeas, resultando uma proporção sexual próxima de 1:1 (0,89:1,00). Todos os espécimens foram capturados por barcos da frota comercial atuneira, que realizaram pescarias com espinhel pelágico, na área localizada entre as latitudes de 08°N e 53°S e longitudes de 08°E e 48°W. Os resultados obtidos sugerem um tamanho de primeira maturação sexual para as fêmeas em torno de 205- 210 cm, e para os machos entre 180- 200 cm de comprimento total (CT). As fêmeas se encontravam em 5 estágios maturacionais: juvenil (n= 29; 35,8%; 74 a 204 cm de CT), em maturação (n= 10; 12,3%; 220 a 295 cm CT), pré-ovulatória (n= 14; 17,3%; 177 a 280cm CT), grávida (n= 24; 29,6%; 203 a 270cm CT); e em repouso (n= 4; 4,9%; 223 a 285 cm CT). Os machos foram classificados em 4 estágios: juvenil (n= 38; 52,8%; 81 a 220 cm CT e Comprimento do Clásper CC < 12 cm), em maturação (n= 16; 22,2%; 166 a 208 cm CT, 9,5 a 24,5 cm CC), Adulto (n= 17; 23,6%; 141 a 272 cm CT; CC > 24,5 cm) e neonato (n= 1; 1,4%; 82 cm CT; 4 cm CC). Foram analisados dados de captura e esforço de pesca de 16.016 lançamentos com espinhel pelágico de deriva, realizados pela frota brasileira atuneira, de 2004 a 2011. A CPUE foi calculada e os dados de captura e esforço foram agrupados em quadrados de 5° x 5° de latitude e longitude. Dois tubarões lombo-preto foram marcados com transmissores via satélite do tipo PSAT (Pop-up Satellite Archival Tag), nas imediações do Arquipélago de São Pedro e São Paulo- ASPSP, mas apenas em um deles foi possível a recuperação dos dados. A faixa de temperatura preferencial do animal marcado se situou entre 27 e 28°C, com uma profundidade preferencial entre 1 e 10m.