Abstract
This study advances techniques to measure the distribution and behavior of steelhead trout in a sea cage in fluctuating tidal currents. An ultrasonic telemetry system (Hydroacoustic Technology Inc., model 291) was deployed around a 63 m3 sea cage stocked with 200 steelhead trout (Oncorhynchus mykiss). Fish and net twine movements were monitored using 20 ultrasonic tags. Eight of these were implanted into the abdominal cavities of sentinel trout, with the remaining attached around the net bottom and midsection. The signals were detected by four omni-directional hydrophones that were connected to a receiver on a nearby pier. Signals detected at 2 s intervals were used to plot three-dimensional locations of thefish. We found that current flow inside the net was significantly reduced (32–53 %) compared to outside, and that swimming behavior was influenced by tidal currents. As current speed increased, the fish swam into the current to maintain their position, and the volume occupied by the eight-sentinel fish decreased. In contrast, during slack tides, the fish swam in a circular pattern, and the sentinel fish used more of the cage volume. This study demonstrates the use of acoustic telemetry to study fish behavior in a cage experiencing tidal currents. This technology can be applied to commercial scale cages to improve fish welfare and cage design.
•Trout behavior based upon environmental changes and net deformation.•Tracking trout with acoustic telemetry.•Measuring net deformation with acoustic telemetry.•Practical information for fish farmers for animal welfare.