Maturation of walleye pollock, Theragra chalcogramma, in the eastern Bering Sea in relation to temporal and spatial factors

Abstract

Walleye pollock, Theragra chalcogramma, are both ecologically and commercially important in the eastern Bering Sea (EBS). Maturity is a critical parameter in the stock assessment to set annual total allowable catch. Pollock maturity has not been examined in the EBS since 1976, and possible interannual and geographic variation has not been studied to date. Our goal is to estimate correct maturity schedules for EBS pollock. Maturity data, fish lengths and macroscopic maturity stages were collected aboard pollock trawlers during winter 2002 and 2003 across the EBS from 10,197 pollock. Similar data were collected by NMFS scientists during hydroacoustic surveys from 1989-2002. Histological analysis of ovary tissue confirmed the appropriateness of macroscopic staging. However, some pollock classified macroscopically as 'developing' may mature either in the current or following spawning seasons. Therefore, our analysis was performed with two alternative assumptions: fish classified as 'developing' were either considered immature or mature. Maturity rates were estimated by logistic regression. Geographic variability exists; fish mature at the smallest lengths north of the Pribilof Islands. Size at maturity varies interannually, as well. Temporal and spatial variation in maturity may be due to biological or environmental factors, such as pollock density, water temperature, or prey availability.