Ultrasonic coded transmitters (UCTs) are high-frequency acoustic tags that are often used to
conduct survivorship studies of vulnerable fish species. Recent observations of differential
mortality in tag control studies suggest that fish instrumented with UCTs may be selectively
targeted by marine mammal predators, thereby skewing valuable survivorship data. In order
to better understand the ability of pinnipeds to detect UCT outputs, behavioral high-
frequency hearing thresholds were obtained from a trained harbor seal (Phoca vitulina) and …