Population dynamics of the data-poor tiger shark (Galeocerdo cuvier) in the Northwest Pacific Ocean: Measurement of growth parameters and mortality rates

Abstract

Although tiger sharks (Galeocerdo cuvier) are found globally in major oceans, comprehensive biological and fishery data pertaining to the Northwest Pacific Ocean are scarce. Accordingly, this study was conducted to understand the challenges in measuring tiger sharks’key life history parameters, including von Bertalanffy growth and mortality rates, which are essential for the construction of robust stock assessment models. To evaluate these parameters, we used the TropFishR software package to analyse observer-recorded length-frequency data acquired from the Nanfangao fish market between January 2015 and December 2022. An electronic length-frequency analysis indicated that the asymptotic length and growth coefficient derived for the combined sexes of the tiger shark population were 366.087 FL cm and 0.245 year−1, respectively. Mortality rates were calculated using a length-converted catch curve and empirical models; the results revealed that the annual rates of total (Z), natural (M), and fishing (F) mortalities were 0.346, 0.168, and 0.178 year−1, respectively. Notably, the observed exploitation rate (E) was slightly high at 0.514 year−1. Our findings may facilitate the development of effective strategies for preserving the tiger shark population in the study region by leveraging this initial information for further stock assessment analyses, thereby enabling a more comprehensive evaluation in the future.