Mortality of Walleye Pollock Escaping from the Codend and Intermediate (= Extension) Section of a Pelagic Trawl

No abstracts are to be cited without prior reference to the author.

Experiments were conducted on a pelagic trawler in the Gulf of Alaska to (a) test trawl gear modifications to improve escapement for undersized walleye pollock (Theragra chalcogramma), and (b) measure mortality of pollock that escape though trawl meshes. Although pollock managed to escape through square meshes of the codend, underwater video showed that these meshes became increasingly blocked as catch volume increased. Therefore, a square-mesh panel was sewn into the intermediate section of the trawl to compensate for this diminished escapement from the codend. Pollock actively escaped intermediate-square meshes as far as 18 m in front of the catch bulge. The survival of fishes escaping trawls should be estimated before gear regulations (e.g., minimum mesh size) are implemented, or when the fishing fleets voluntarily use devices, such as escape panels, to enhance escapement from their gear. Unless substantial amounts of fish escaping from trawls survive, conservation regulations implemented to permit escapement may be of little value. A caging method was used to capture escapees at trawling depth. These fish were held in sea-bed cages and checked once or twice per day for 14 days by SCUBA divers. Although many pollock that escape through trawl meshes survived, our results suggest potentially significant levels of size-dependent mortality. Management implications of these results are discussed.