Tracking the movements of juvenile Chinook salmon using an autonomous underwater vehicle under payload control

An autonomous underwater vehicle (AUV) under payload control (PC) was used to map the movements of juvenile Chinook salmon (Oncorhynchus tshawytscha) tagged with acoustic transmitters. After detecting a tag, the AUV deviated from its pre-programmed route and performed a maneuver designed to enhance the location estimate of the fish and to move closer to collect proximal environmental data. Nineteen fish were released into marine waters of southeastern Alaska. Seven missions with concurrent AUV and vessel-based surveys were conducted with two to nine fish present in the area per mission. The AUV was able to repeatedly detect and estimate the location of the fish, even when multiple individuals were present. Although less effective at detecting the fish, location estimates from the vessel-based surveys helped verify the veracity of the AUV data. All of the fish left the area within 48 h of release. Most fish exhibited localized movements (milling behavior) before leaving the area. Dispersal rates calculated for the fish suggest that error associated with the location estimates was minimal. The average movement rate was 0.62 body length per second and was comparable to marine movement rates reported for other Chinook salmon stocks. These results suggest that AUV-based payload control can provide an effective method for mapping the movements of marine fish.