Length-based Estimates Of Growth And Natural Mortality For Blue Marlin (Makaira Nigricans) In The Northwest Pacific Ocean

Abstract

Blue marlin is an important resource for commercial and recreational fisheries. However, several life history parameters needed for stock assessments of this species are poorly determined. Sex-specific catch-at-size data (eye fork length, EFL) for blue marlin were collected from the Taiwanese offshore longline fishery in the northwest Pacific Ocean, and analyzed using the MULTIFAN, a length-frequency analysis, to derive growth parameters. The von Bertalanffy growth parameters of blue marlin were estimated to be different between sexes. The best model for the females included 11 age-classes in the length frequency data sets (asymptotic length L-infinity = 312.5 cm EFL, growth coefficient k = 0.111 yr(-1), and theoretical age at zero length t(0) = -2.42 yr), while 9 age-classes were identified for the males (L-infinity = 232.8 cm EFL, k = 0.131 yr(-1), and t(0) = -3.58 yr). Natural mortality rates, based on empirical equations, were estimated to be 0.258 yr(-1) for the males and 0.213 yr(-1) for the females, respectively. The estimates of growth parameters and mortality rates derived from this study could be used in stock assessments for blue marlin, and contribute towards the fisheries management of the species.