A Comparison of Methods for Classifying Female Sablefish Maturity and Skip Spawning Outside the Spawning Season

Abstract

AbstractOvarian development in Sablefish Anoplopoma fimbria was classified using three methods for samples collected during July and August in the Gulf of Alaska, approximately 6–8 months prior to spawning. Although not an ideal time for predicting future spawning, this is when survey platforms, such as longline and trawl vessels, are available annually. The three maturity classification methods included (1) macroscopic classification at sea by trained scientists but with these personnel varying throughout the survey period, (2) macroscopic classification after the survey from photographs by a single, highly trained scientist (standardized macroscopic), and (3) a microscopic evaluation of ovarian structures from histological slides. Based on certain oocyte development characteristics, the second half of August was identified as the time period when maturity could be the most accurately classified in the Gulf of Alaska. Age and length at maturity were estimated to be earlier or smaller, respectively, on some portions of the survey, when macroscopic at‐sea methods were used as opposed to standardized macroscopic or microscopic methods. Skip spawning was documented throughout the survey but at a lower rate than was reported in other studies (2% versus 6% and 21%), indicating that the rate of skip spawning is likely variable. The results demonstrate that accurate maturity classifications may be determined from collections during nonpreferable months when histology or the standardized macroscopic method is used. Identifying skip spawning is likely reliant on microscopic analysis, and so a combination of the standardized macroscopic method along with limited histological sampling, to identify skip spawning rates or to classify maturity when there is uncertainty at sea, may be the most time‐ and cost‐effective option for species similar to Sablefish that skip spawn.