Abstract
To better manage fish populations, scientists and fisheries managers use age and growth studies to conduct stock assessments or provide management advice. However, many non-targeted species, important to the marine ecosystem, such as Pseudocarcharias kamoharai still lack such studies which impede comprehensive management of the fisheries. This study presents the age, growth, and sexual maturity of this species from the Tropical Eastern Atlantic Ocean (TEA) by examining vertebral samples. All samples were collected by Chinese Tuna Fishery Scientific Observers between November 2012 and May 2020, with sizes ranging from 46 to 101 cm fork length (FL). Four age determination approaches applied on whole and sectioned vertebral centra were compared. Four growth models fitted to the age data were also compared and the AIC was used to select the most plausible model. Whole vertebral centra stained with alizarin red S solution showed clearer growth band-pairs, and age ranged from 2 to 10 years (females) and from 2 to 11 years (males). The three-parameter von Bertalanffy growth function presented the best fit to describe the growth of this species. The obtained parameters for males were L∞ = 110.4 cm FL, K = 0.26 year-1 and L∞ = 108.3 cm FL, K = 0.29 year-1 for females. Females reached their size at 50% maturity (FL50%) larger than males (80.5 and 74.5 cm FL, respectively). The estimated longevities were 11.95 and 13.33 years for females and males, respectively. More work is needed regarding P. kamoharai in different Oceans, though, this study adds significant life-history information that can contribute to the management and conservation of the species.
Highlights
Pelagic longline fisheries primarily targeting tuna and swordfish in oceanic waters worldwide catch important numbers of pelagic sharks, increasing concerns about the worsening status of their populations (Dulvy et al, 2008)
Considering the lack of life-history information concerning P. kamoharai in the Tropical Eastern Atlantic (TEA), especially concerning age, growth and sexual maturity, this study aims to (1) estimate the age of P. kamoharai specimens through the reading of growth bandpair counts deposited on vertebral centra; (2) compare age enhancement techniques to determine which can better assess the age of P. kamoharai; (3) compare and obtain best growth models for this species; (4) determine sexual maturity ages for both sexes; and (5) provide age, growth, and reproductive data for population status assessments important to guide management measures necessary for the conservation of the species
The largest female was caught during the first voyage in December 2012 having a length of 101 cm, bigger than the largest male, with a mean fork length (FL) ± SD of 81.14 ± 7.96 cm while the mean FL ± SD for male specimens was 78.46 ± 6.28 cm
Summary
Pelagic longline fisheries primarily targeting tuna and swordfish in oceanic waters worldwide catch important numbers of pelagic sharks, increasing concerns about the worsening status of their populations (Dulvy et al, 2008). 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
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