Release Mortality of Pacific Halibut from Commercial and Recreational Fisheries - a 50 Year Perspective

The International Pacific Halibut Commission has been conducting release mortality studies since the 1950s first estimating tagging mortality but later expanding to bycatch mortality from fishing gears. In the late 1960s, tag recovery rates were used to estimate relative mortalities associated with fish size, tow duration, and time on deck. This study introduced a five-category condition index.  In an 1989 reanalysis, this was collapsed into three groups which are still in use. In the mid-1990s, we developed injury criteria for estimating the mortality of halibut released from hook and line gear. Survival was estimated for hook removal injuries associated with a number of careful release procedures, as well as releases using a hook stripper. Results from these studies have identified mortality for these gears according to various types of bycatch handling. When combined with observer data collection, this allows the calculation of discard mortality rates by fishery and area. Importantly, these approaches represent long term mortality, due to the use of tag recovery data from several years. Results of these and other studies will be presented and discussed.