Laboratory and Field Experimental Validation of Two Different Predation Sensors for Instrumenting Acoustic Transmitters in Fisheries Research
Robert J. Lennox, Cecilie I. Nilsen, Ainslie Nash, Erlend M. Hanssen, Hilde L Johannesen, Saron Berhe, Bjørn T. Barlaup, Knut Wiik Vollset
Abstract
Abstract We validated the performance of two types of predation sensors on acoustic telemetry transmitters in a combined field and laboratory study design using juvenile Atlantic Salmon Salmo salar and a predator large Brown Trout Salmo trutta. One tag model was outfitted with an acid-sensitive predation sensor, and the other was equipped with a tilt-based orientation sensor. We found similar response times for the two tag types to identify a predation event (time between known ingestion of a tagged fish and triggering of the predation sensor). However, the orientation sensor model was more accurate in laboratory trials, correctly identifying 100% of events in which predators were fed the tagged fish, whereas correct identification of predation events was 50% for the acid-sensitive sensor in similar trials. The acid-sensitive tags were smaller (0.65 g in air), and all 10 were eventually expelled by predators in the laboratory (2–22 d after tag ingestion). By contrast, only two of five tags with orientation sensors (1.4 g in air) were expelled in a similar period (13 and 16 d after tag ingestion). Both tags had distinct benefits: acid-sensitive sensor tags were very small, and orientation sensor tags were seemingly more accurate and transmitted raw orientation data to receivers for postprocessing.