Characterizing behavioral responses of Pacific cod to bottom trawl vessels and gear using archival tag accelerometer data

Abstract

Fish behavior during the capture process affects the overall efficiency of survey vessels and gear, influencing selectivity and catchability, which in turn influences stock assessments. The effects of behavior on capture are typically investigated through experiments that use video or acoustic technologies to observe behavioral responses of fish to vessels and gear directly. While these approaches provide valuable information about fish behavior, their use is limited to observing the movement of fish inside a small observed area. In this proof-of-concept study, we demonstrate a novel application of bio-logging Pop-up Satellite Archival Tags (PSATs) equipped with accelerometer sensors to observe behavioral responses of free-swimming demersal fish to approaching bottom trawl fishing vessels and gear. By combining PSAT and fishing vessel geolocation data from the Vessel Monitoring System, we characterized diving and herding responses of three individual Pacific cod (Gadus macrocephalus) at-liberty for 21–106 days to trawling fishing vessels. We found that fish descended as trawlers approached, presumably in response to noise generated by the fishing vessel and gear, which supports the previously untested hypothesis that Pacific cod dive in response to approaching fishing vessels and gear, similar to closely related gadids. Additionally, one 88 cm fish swam ahead of a trawl towed at 1.25 m·s−1 (i.e., 1.42 body lengths per second) for 55.6 minutes, covering a distance of 4.17 km before capture, which challenges previous assertions that Pacific cod are unlikely to outswim bottom trawl gear towed at typical towing speeds. This study demonstrates that opportunistically collected archival tag data can be used to improve knowledge of behavioral interactions between fish and fishing gear.