Postrelease survival of green sturgeon (Acipenser medirostris) encountered as bycatch in the trawl fishery that targets california halibut (paralichthys californicus), estimated by using pop-up satellite archival tags

Abstract

Understanding postre-lease effects of incidental capture on fish species of conservation concern is critically needed. We collaborated with commercial fishermen to estimate postrelease survival of green sturgeon (Acipenser medirostris) captured and released from bottom trawls used to target California halibut (Paralichthys californicus). We developed a method for interpreting acceleration, depth, and temperature data transmitted from pop-up satellite archival tags to classify the fate of individuals follow-ing capture and release in fishing oper-ations. We first deployed SeaTag-MOD satellite tags on known living and dead sturgeon to develop a support vector machine that uses accelerometer read-ings to classify tagged fish as alive or dead. In 2015 and 2016, fishermen and West Coast Groundfish Observer Program observers tagged 76 green sturgeon (69–135 cm fork length) encountered as bycatch, yielding 51 useable data sets. Eleven sturgeon were classified as having died after release, 9 of which died within our designated 21-d (504 h) study period. Some green sturgeon entered the San Francisco Bay Delta after being tagged, indicating movement between ocean and estuary environments. Research is needed to understand how to mini-mize effects of handling time and trawl bycatch mortality.