Reproductive Biology, Size, and Age Structure of Harlequin Rockfish: Spatial Analysis of Life History Traits

Abstract

Many rockfish (genus Sebastes) species within multispecies complexes have lacked basic biological data hindering their fisheries management. In this study, we provide essential information for stock assessment decision making for one of these species, Harlequin Rockfish Sebastes variegatus. We analyzed aspects of reproduction, size structure, and growth of Harlequin Rockfish in waters off Alaska using historical survey data and recent field collections. Results are reported primarily from the Gulf of Alaska (GOA) region, but important findings are noted from the Aleutian Islands (AI). Harlequin Rockfish reached an observed maximum age of 76 years in the AI, a new estimate for this species. Females exhibited group-synchronous oocyte development; the parturition period occurred in the spring in both regions, ceasing as late as July in the GOA. Females from the GOA had an estimated length and age at 50% maturity of 187.6 mm (95% confidence limits [CL] = 152.0–215.6 mm; n = 318) and 4.7 years (95% CL = 1.6–6.2 years; n = 188), respectively, indicating that the Harlequin Rockfish is one of the earliest maturing rockfishes. We analyzed a 14-year time series of bottom trawl survey data to examine the relationship between Harlequin Rockfish length and selected covariates. Spatial heterogeneity existed, with size showing a relationship with bottom temperature and ocean color (productivity index) across the GOA. The comparison of Harlequin Rockfish length at age indicated that larger fish were present in the western GOA but variable growth occurred across the region. Our findings contribute to understanding Harlequin Rockfish biology within multispecies management complexes, and our results demonstrate that key life history traits vary spatially, possibly influenced by regional environmental conditions. This study represents the most comprehensive biological examination for Harlequin Rockfish.