Estimated female sablefish spawning biomass and projection.

The Alaska Fisheries Science Center models the entire federally managed Alaska sablefish fishery as one population, integrating data from the Bering Sea, Aleutian Islands, and the Gulf of Alaska. The model is sex-specific because males and females have different growth and maturity rates, and females attain larger maximum sizes.

The model incorporates data from a variety of sources such as the historical Japanese longline survey and fisheries, the annual domestic NMFS longline survey, the biennial NMFS bottom trawl survey in the Gulf of Alaska, and the domestic fixed and trawl gear fisheries. The data provided by these sources include catch, relative abundance, age and length compositions, size-at-age, and maturity-at-age.

The model is a separable age-structured model coded in AD Model Builder, which uses a maximum likelihood and Bayesian approach to estimate parameters such as fishing mortality, absolute abundance, selectivity, and catchability. The model is updated annually in conjunction with new longline survey data. The model is also used to project the population forward in time to calculate fishing mortality and quotas for subsequent years under various scenarios. These quotas are allocated to smaller management areas by computing a weighted 5-year average of survey and fishery catch rates by area. Bayesian MCMC methods are used to quantify the uncertainty of estimates.

Current estimates indicate that there were two peaks in biomass (1970 and 1990), with periods of low recruitment and heavy fishing leading to rapid declines. Several above average year classes have recently returned spawning biomass close to the target level.

Estimates of recruitment (age 2) for sablefish.

Contact:
Dana Hanselman
Auke Bay Laboratories
Alaska Fisheries Science Center, NOAA Fisheries

Ted Stevens Marine Research Institute
17109 Pt Lena Loop Rd
Juneau AK 99801
Dana.Hanselman@noaa.gov