| Summary: | Halibut bycatch in trawls limits Alaska trawl fisheries and greatly concerns stakeholders from local communities and fisheries that rely on halibut. As part of ongoing efforts to reduce halibut mortality, Alaska Seafood Cooperative (AKSC) plans a trial implementation of procedures to sort halibut from catches earlier than now allowed. We supplemented that effort by measuring survival rates of released halibut. In this study, pop-up satellite archival tags (PSATs) attached to halibut recorded their activity for 2 months following release, indicating survival outcomes. Pre-release condition from viability assessments and handling parameters supported analyses for survival prediction. Tapes of viability assessments allowed detailed review of release condition. Results will support consideration of regulatory changes required to routinely allow expedited sorting, as well as providing insights into the assessment and conditions affecting halibut viability. The research team included scientists experienced with collaborations with the trawl fleet and local communities, and from the IPHC, as well as the leader of the overall AKSC effort. During the summer of 2016, 160 PSAT tags equipped only with accelerometer sensors were deployed on Pacific halibut, following capture and release from three trawler-processors conducting deck-sorting trials in the Bering Sea. Specifically, pop-up satellite archival tags were attached to 1) 160 deck-sorted (trawl caught) halibut, 2) 10 long-line caught halibut, 3) 6 fixed anchors, and 4) 4 known dead halibut. PSATs were attached to halibut or anchor on a tether, so the positively buoyant tag floats freely in a vertical orientation above the fish when the fish is not active. During active swimming, drag forces cause the tag orientation to become horizontal as it is towed by the fish. Accelerometers on the tag provide information on whether the PSAT is vertical or horizontal. The objectives of this project were to use discard mortality rates based from viability assessments (from video recordings), post-release survival estimates provided by pop-up satellite archival tags and handling factors influencing survival (e.g., specimen time on deck, tow time, air exposure, fish size, air temperature, and catch size), to 1) estimate the survival rate of halibut discarded by Bering Sea flatfish trawlers through expedited release, 2) identify possible handling factors influencing survival, and 3) compare tag-reported survivals over a period of months to survival rate estimates based on current viability score methods. This dataset was generated as part of NPRB project 1510. Data from a pilot study (Port Frederick Test Tags.zip) and deck videos have not been published with this dataset but are available upon request. Please contact the Principal Investigator for more information.
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