Age and Sex-Specific Sablefish Movement in Alaskan Waters

Sablefish in Alaskan waters support a large and economically valuable fishery.  In Alaskan waters, the sablefish fishery is managed by discrete geographic areas. Previous tagging studies of sablefish revealed long-term ontogenetic movement throughout Alaskan waters.  To facilitate effective spatial management policies for sablefish and as preparation for development of a spatial assessment model, a movement model based on conventional tagging data from 1983 to 2009 was developed.  This model   estimates age and sex-specific movement rates and is an extension of a previously developed discrete time and space movement model that allows for monthly movement between spatial strata.  The spatial domain of the model has six spatial strata, five for Alaskan waters and one for British Columbia, though only tag releases from Alaskan waters are considered.   Ages in the model ranged from 2 to 20 years with an age 20 “plus” group.   A suite of models with different assumptions about age and sex-specific movements were developed. Akaike Information Criterion (AIC) values supported increasingly complex movement dynamics but the precision of estimated movement probabilities decreased with model complexity.  AIC values supported age and sex-specific movement dynamics, but movement probabilities did not typically differ greatly among the sexes for a particular age group.    Estimated movement probabilities give some support to the prevailing paradigm of movement of younger sablefish from southeast Alaska to the western Gulf of Alaska and Aleutian Islands and return movement to the southeast for older fish, though movement probabilities for fish in the Aleutian Islands stratum and Bering Sea stratum were highly imprecise.  Results of this modeling study confirm assumptions about age-based based sablefish movement but are equivocal about sex-specific movement rates.  Alternative model configurations to reduce uncertainties in estimated movement probabilities will be briefly discussed.