Decreasing length at age in a rapidly expanding population of northern rock sole in the eastern Bering Sea and its effect on management advice

The highly productive eastern Bering Sea shelf has undergone a dramatic inc rease in the size of flatfish stocks during the last 20 years. This has bee n highlighted by the northern rock sole stock. which has increased well ove r 15 times from approximately 175 x 10(6) kg in 1975 to nearly 3 x 10(9) kg in 1994. Annual bottom trawl surveys and an age-structured population mode l have been used to track the increase. A new evaluation of the data has shown significant decreases in length-at-a ge (and resultant weight-at-age) as the population increased and expanded w estward toward the shelf edge. The downward trend in length-at-age primaril y affected year classes between 1979 and 1987. A small increase has occurre d subsequently. Potential density-dependent relationships are examined with the significant regression of mean length at age-3 versus population chang es. These differences in growth were incorporated into a stock assessment m odel to examine their effect on estimates of recruitment variability, fluct uations in stock biomass and yield recommendations. Published by Elsevier S cience B.V.