Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean

Abstract

This study used data provided by the Chinese Longline Fishery Scientific Observer Programme from the tropical eastern Atlantic Ocean to estimate the reproductive parameters of the blue shark (Prionace glauca) and crocodile shark (Pseudocarcharias kamoharai). Sizes ranged from 80 to 298 cm fork length (FL) for blue sharks and from 48 to 99 cm FL for crocodile sharks. Sexual segregation was observed during different months for both sharks. The sex ratio for blue sharks was 1.38 F:1 M, and 1 F:2.79 M for crocodile sharks. The size of adult blue sharks ranged from 144 to 280 cm for males and from 174 to 298 cm for females; and that of crocodile sharks from 63 to 97 cm for males and 78-99 cm for females. The size at 50% of maturity for blue sharks was estimated at 191.7 cm FL for females and 197.5 cm FL for males, and that of crocodile sharks was assessed at 84.9 cm FL for females and 78.5 cm FL for males. Most sexually matured females were pregnant; their means were 207.2 ± 16.4 cm FL for blue sharks and 89.4 ± 4.3 cm FL for crocodile sharks. Mature sizes for both species were significantly different among months. Embryonic sizes also varied widely among months for crocodile sharks, but a slight change was recorded for those of blue sharks. The observed mean size at birth and litter size were 34.5 cm FL and 37 ± 12 for the blue sharks, and that of the crocodile sharks, 39.5 cm FL and a dominant four embryos in the uterus. Due to the observed increasing catch trend of blue sharks and the slow reproductive cycle of crocodile sharks, this study presents the need of implementing conservation measures to ensure the sustainability of both species in their habitat.

Age, Growth, and Sexual Maturity of the Crocodile Shark, Pseudocarcharias kamoharai, From the Eastern Atlantic Ocean

“…The second model used was a two-parameter VBGF, following the equation above, with L 0 fixed to the size at birth of 39.5 cm FL described for this species considering observations in Wu et al (2020).…”

“…For both male and female specimens, the maturity stages were defined according to the previous study of P. kamoharai in the TEA (Wu et al, 2020). Reproductive organs were examined and categorized mainly according to the developmental stages of the ovaries and uteri in females, and claspers in males.…”

“…Reproductive organs were examined and categorized mainly according to the developmental stages of the ovaries and uteri in females, and claspers in males. Male sharks were classified into two stages and females into four stages, as detailed in Wu et al (2020). Relationships between the FL and reproductive organs including clasper length, the width of the oviducal glands and uterus were determined.…”

“…Despite its worldwide distribution, P. kamoharai has been rarely studied and little is known about its life-history due to lack of data mainly because it is caught as bycatch and discarded in tuna and swordfish fisheries worldwide (Fujita, 1981;Compagno, 2001;Romanov et al, 2008;Oliveira et al, 2010;Dai et al, 2011;Coelho et al, 2012) and in artisanal fisheries (Martínez-Ortiz et al, 2015). P. kamoharai is ovoviviparous, with uterine oophagy and 2-4 pups per litter (usually 4, two from each uterus), which can vary between 31.57 and 40.35 cm FL at the end of the gestation period (White, 2007;Oliveira et al, 2010;Lessa et al, 2015;Wu et al, 2020). Sexual maturity of both sexes are attained almost at similar body lengths; females mature at lengths between 69.79 and 89.77 cm FL and males from 63.27 and 78.5 cm FL (White, 2007;Oliveira et al, 2010;Dai et al, 2011;Wu et al, 2020).…”

“…P. kamoharai is ovoviviparous, with uterine oophagy and 2-4 pups per litter (usually 4, two from each uterus), which can vary between 31.57 and 40.35 cm FL at the end of the gestation period (White, 2007;Oliveira et al, 2010;Lessa et al, 2015;Wu et al, 2020). Sexual maturity of both sexes are attained almost at similar body lengths; females mature at lengths between 69.79 and 89.77 cm FL and males from 63.27 and 78.5 cm FL (White, 2007;Oliveira et al, 2010;Dai et al, 2011;Wu et al, 2020). In the western Atlantic Ocean, Lessa et al (2015) reported that age-atfirst maturity for male specimens was achieved at 3.1 years and females at 5.1 years.…”