Size, sex and reproductive biology of seven pelagic sharks in the eastern Arabian Sea

Abstract

Studies on reproduction in sharks are important for their management, since the attainment of sexual maturity has a substantial impact on their distribution, behaviour and biology. However, reproductive biology of large oceanic sharks is poorly studied in the Indian seas. In this study, the size structure, sex and maturity of pelagic thresher (Alopias pelagicus), bigeye thresher (A. superciliosus), oceanic whitetip shark (Carcharhinus longimanus), tiger shark (Galeocerdo cuvier), shortfin mako (Isurus oxyrinchus), longfin mako (I. paucus) and blue shark (Prionace glauca) in the eastern Arabian Sea are described based on 1449 specimens collected from gillnet-cum-longline landings at the Cochin fisheries harbour during 2013–2014. Sex ratios of sampled specimens were biased to males in pelagic thresher, bigeye thresher, tiger shark and blue shark, while females dominated in the specimens of oceanic whitetip shark. Females matured at greater lengths than males in all species except oceanic whitetip shark. Lengths at maturity for males were in the range of 189.05–286.56 cm, whereas those of females were in the range of 187.74–310.69 cm. Litter sizes of both the thresher shark species were always two, while in oceanic whitetip shark, litter size was 3–9 and 22–51 in tiger shark. Seasonal reproduction was noticed in oceanic whitetip shark and tiger shark. Pregnant females were not found in the blue shark, shortfin and longfin makos sampled during the study period. Reproductive aspects of pelagic thresher, bigeye thresher, oceanic whitetip shark, tiger shark, shortfin mako, longfin mako and blue sharks in the eastern Arabian Sea are generally consistent with earlier reports from other regions of the world's oceans. These preliminary findings should be useful to identify suitable management measures for the above shark species.

Reproductive Biology and Distribution of the Blue Shark (Prionace glauca) in the Western Indian Ocean

“…Additionally, the results of this study were slightly lower than the 2021 IOTC report on the status of blue sharks in the Indian Ocean, which showed a male sexual maturity length of 201 cmTL. Similar results were also reported in studies conducted by [ 10 , 28 ]. The length at sexual maturity for females was similar to the global average reported size [ 27 ] but higher than the 194 cmTL reported in the 2015 IOTC report on the status of blue sharks in the Indian Ocean and the study by [ 10 ].…”

Local drivers of declining shark fisheries in India

“…Several fishery dependent surveys in waters of the Arabian Sea have indicated that the abundance of both species has drastically declined (e.g. Varghese et al 2017). Furthermore, a regional Arabian Sea and adjacent waters IUCN Red List of Threatened Species assessment has evaluated them as Critically Endangered and Endangered, respectively, suggesting population declines between 50 and 80% over the past 50-60 years (Jabado et al 2017).…”

Effect of Life History on Alopias pelagicus Overexploitation Vulnerability: A Literature Review

“…A. pelagicus also exhibits an annual reproductive cycle [16]. Research conducted by Varghese et al [18] stated that A. pelagicus did not have a resting phase in its reproductive cycle.…”

“…The reproductive strategy of A. pelagicus is closely related to several parameters, thus are, reproductive strategy; size at birth, size-at-maturity, age-at-maturity, gestation period, reproductive cycle, and sex ratio in embryos [10, 16,18]. A study conducted by Varghese et al [18] showed that during the 9-month gestation period, A. pelagicus has a reproductive strategy of aplacental viviparity by embryonic oophagus. Oophagus means eating eggs, in this reproductive strategy additional nutrients are given to developing embryos in the form of unfertilized eggs.…”