Sex Ratio, Spawning Period, and Size and Age at Maturity of Sablefish Anoplopoma fimbria Off Northern California

Abstract

Size, sex, state of maturity and age were determined for sablefish captured by commercial otter trawl vessels at depths from 100 m to 900 m off northern California from January through August 1984. Sex ratios appeared to be 1: 1 among immature fish at all depths, but significantly departed from a 1: 1 ratio among mature fish during many months and at many depths, without any clear pattern. Plots of percent spent fish against month suggested that spawning took place from late January through March with a probable peak during early February. Estimated fork lengths at 50% maturity showed a shift to a smaller size with increasing depth. A greater fraction of males and females was mature at smaller sizes and younger ages in deeper waters (>600 m) than in shallow waters (<600 m). Maturation of both sexes occurred over a wide range of ages and sizes (from 3 to 8 years of age and from 40 to 65 cm in fork length), although females generally matured at a larger size and older age than males. Two alternative hypotheses could explain collected data. Sablefish may move to deeper waters at the onset of sexual maturity (for which size and age may vary considerably among individuals), or distinct deep water and shallow water stocks may exist off northern California. Tagging experiments are necessary for distinguishing between these alternative explanations. © 1988, The Japanese Society of Fisheries Science. All rights reserved.