Age and growth of North Pacific albacore (Thunnus alalunga): Implications for stock assessment

Abstract

Accurate estimates of age and growth parameters are important for fisheries management because these values affect stock assessment models. Age and growth of North Pacific albacore (Thunnus alalunga) was assessed by examining annual growth increments in sagittal otoliths from 486 fish collected in different regions of the North Pacific Ocean. A wide size range of albacore (52–128cm fork length, FL) was collected in an attempt to incorporate size-at-age information over juvenile, sub-adult, and adult life history stages. Overall, ages ranged from 1 to 15 years, with the majority of fish between 2 and 4 years of age. Growth models fit otolith-based size-at-age well, and Akaike's Information Criterion corrected for small sample size indicated that the specialized von Bertalanffy (VB) model provided the best fit. The estimated biological parameters of the specialized VB model were L∞=124.1cmFL, K=0.164year−1, and t0=−2.239. Daily ages were also determined and verified correct age-1 assignments for fish 55–61cmFL, with daily ages ranging from 378 to 505 days. In addition, dorsal fin spines and length frequency (LF) analysis were used to obtain estimates of size-at-age and corroborated results from otolith-based techniques. Modeling exercises resulted in nearly an order of magnitude difference in spawning stock biomass (SSB) when comparing growth parameters obtained from this study relative to previous stock assessment models of North Pacific albacore. Results suggest North Pacific albacore is a relatively long lived tuna species and provide updated biological parameters useful for future stock assessment models.