Application of Machine Learning and Acoustic Predation Tags to Classify Migration Fate of Atlantic Salmon Smolts

Abstract Mortality and predation of tagged fishes presents a serious challenge to interpreting results of acoustic telemetry studies. There is a need for standardized methods to identify predated individuals and reduce the impacts of “predation bias” on results and conclusions. Here, we use emerging approaches in machine learning and acoustic tag technology to classify out-migrating Atlantic salmon (Salmo salar) smolts into different fate categories. We compared three methods of fate classification; predation tag pH sensors and detection data, unsupervised k-means clustering, and supervised random forest combined with tag pH sensor data. Random forest models increased predation estimates by 9-32% compared to pH sensor data, while clustering reduced estimates by 3.5-30%. The greatest changes in estimates were seen in years with large class imbalance or low model accuracy. Both supervised and unsupervised approaches were able to classify smolt fate, however, in-sample model accuracy improved when using tag sensor data to train models, emphasizing the value of incorporating such sensors when studying predator-prone fish. Sensor data may not be sufficient to identify predation in isolation due to Type I and Type II error in predation sensor triggering. Combining sensor data with machine learning approaches should be standard practice to more accurately classify fate of tagged fish.