KMR assisted a project to detect and assess bycatch mortality of Pacific halibut in trawl fisheries (Craig Rose, FishNext Research LLC, P.I.). This project was funded by the North Pacific Research Board and the NOAA Saltonstall-Kennedy Grant Program.

We used Pop-up Satellite Archival Tags (PSATs) fitted with tri-axial accelerometers to characterize activity patterns for halibut. These tags record acceleration on all 3 axes every second. The PSAT is attached to the fish with a dart and a tether, so the positively buoyant tag floats in a vertical position while the halibut is stationary. When the halibut starts to swim, the tag is pulled backwards by drag forces and switches to a horizontal orientation. The vertical accelerometer records the full force of the earth's gravity when the tag is vertical (1 g), and none while the tag is horizontal (0 g). Although the tags will measure acceleration due to gravity (which provides information on the orientation of the tag) and the dynamic acceleration associated with a change in velocity of the tag itself, the dynamic acceleration of fish typically occurs at a much higher frequency ( > 30 hz) than the tag measurement interval (1 hz). Therefore the acceleration values generally reflect the orientation of the tag rather than the acceleration of the tag itself (though some dynamic acceleration does occur). The PSAT tilt (vertical axis) data provide clear patterns of fish activity that can be summarized for transmission to satellites. Activity patterns can be used to assess survival of halibut caught in trawls, or as bycatch in any fishery.

A poster produced for the 2017 International Biologging Symposium provides more information on how PSATs with accelerometers can be used to characterize halibut activity patterns and identify bycatch mortality. You can also watch a video that shows the motion of the PSAT when a halibut swims. Read the peer-reviewed manuscript that describes methods for using accelerometer data to assess activity and mortality.