Age and growth of the blue shark (Prionace glauca) in the Indian Ocean

I Andrade,D Rosa,R Muñoz-Lechuga,R Coelho

doi:10.1016/j.fishres.2018.11.019

I Andrade, D Rosa + Show 2 more

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https://doi.org/10.1016/j.fishres.2018.11.019

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Abstract

Since there is still a lack of biological information regarding Prionace glauca in the Indian Ocean, specifically in terms of age estimation and growth modelling, the age and growth of this species was studied by analysing vertebral samples. All samples were collected from specimens captured by pelagic longliners between March 2013 and September 2016, with sizes ranging from 82 to 301 cm fork length (LF). Two growth models were fitted to the age data, a three-parameter von Bertalanffy growth function (VBGF) re-parameterized to calculate L0 (size at birth) and a two-parameter VBGF with a fixed L0. The latter was considered the most adequate to describe the growth of the species, with the estimated parameters being L∞ = 283.8 cm LF, k = 0.13 year−1 for males and L∞ = 290.6 cm LF, k = 0.12 year−1 for females. These results suggest that females have a slower growth than males. The maximum age estimated was 25 years, representing the oldest attributed age to this species so far. Further work is needed regarding P. glauca in the Indian Ocean, but this study adds important life-history information that can contribute for the management and conservation of the species.

Highlights

The blue shark Prionace glauca (L. 1758) is the only species belonging to the genusPrionace which belongs to the Carcharhinidae Family (Order Carcharhiniformes)
Sample characteristics A total of 818 vertebrae of P. glauca specimens were collected for the present study, of which 491 (60%) were from male sharks and 327 (40%) were from females
In the present work, two new growth curves were obtained for P. glauca in the Indian Ocean, one for males and the other for females, with new estimated growth parameters

Summary

Introduction

The blue shark Prionace glauca (L. 1758) is the only species belonging to the genusPrionace which belongs to the Carcharhinidae Family (Order Carcharhiniformes). Regarding the distribution of P. glauca in the Indian Ocean, results of a recent study by Coelho et al (2018) suggest that larger individuals are found in equatorial and tropical parts of this ocean, while smaller specimens seem to prefer higher latitudes Sharks belonging to this species can be longer than 300 cm in total length (LT) (Pratt, 1979) and have been suggested to reach as much as 380 cm LT (Compagno, 1984). The longevity of P. glauca is thought to be of about 20 to 23 years (Cailliet et al, 1983; Manning & Francis, 2005;; Stevens, 2009)

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