A megafauna in distress: Unsustainable exploitation of tiger sharks in the Arabian Sea and implications for conservation

Abstract

Populations of the iconic tiger shark, Galeocerdo cuvier, are in a state of global decline, with the species assessed as ‘Near Threatened’ on the IUCN Red List. Despite this, there is a lack of fundamental information required for regional management, such as those on life history and ecology. We bridge this knowledge gap by generating the first information on the population dynamics of G. cuvier from the Arabian Sea – one of the world's most important shark fishing regions. Length-frequency data of 629 G. cuvier landed at Cochin (Southwest coast of India) over 16 months in 2023–2024, revealed the dominance of 180–240 cm length class, with the largest individual measuring 405 cm TL. The von Bertalanffy curve fitted to the length-frequency data revealed greater asymptotic length (L_∞ = 490.55 cm TL) and growth co-efficient (K = 0.250 y⁻¹) compared to populations from the Atlantic and Pacific. Estimates of fishing mortality (F = 0.77) and exploitation rate (E = 0.71) suggest that G. cuvier face high levels of fishing pressure. The length at first capture (L_C) indicates that close to 95 % of the catches are represented by immature individuals. In addition, young of the year G. cuvier (<150 cm TL) landed as ‘bycatch’ contributed to 23 % of the landings. To effectively mitigate these challenges, and secure the future of G. cuvier in the Arabian Sea, we propose the establishment of tiger shark conservation zones to help protect critical life-history stages, and implement size-based restrictions to reduce growth and recruitment overfishing.