Injury, condition, and mortality of Pacific halibut bycatch following careful release by Pacific cod and sablefish longline fisheries

Abstract

Pacific halibut caught as bycatch or intended for discard by longline vessels in US and Canadian waters of the north Pacific must be removed from the hook using careful release techniques required by regulation. In many fisheries, trained observers subsample the released halibut for fish condition. These condition codes are used to track cumulative bycatch mortality in these fisheries. Tag return rates of halibut released from longline gear near Kodiak Island, Alaska, are used to estimate relative and absolute mortalities of fish by release method, hook removal injury, and condition code. Generally, the proper application of the careful release techniques results in only minor hook removal injuries. Survival rates of moderately and severely injured halibut are 1.5–2 times higher than previously assumed. One result of our study is the finding that not all fish judged at tagging as likely to die actually die. We recommend a reworking of the condition code methodology.