Grey seals (Halichoerus grypus) learn to use sounds from acoustic fish tags as an indicator of food location.
The negative effects of anthropogenic noise on marine mammals can be pronounced, such as lethal whale strandings coinciding with exposure to military sonar. Acoustic deterrent devices (ADDs) aim to elicit avoidance responses in aquatic predators, such as seals, and are currently being used to reduce depredation in fisheries. However, seals that have previously found fish at a location close to an ADD quickly habituate to these sounds.
In other cases seals quickly learned that sounds emanating from research tags put on fish are the equivalent of a dinner bell. For years, scientists have used “pinging” tags that emit sound to study the population size, migratory movements, and longevity of many fish species. But they also have noticed that in some studies, the noise-making fish did not fare as well as fish tracked with silent tags.
Observational evidence suggests that ADDs may attract predators and in such cases may even cause higher incidences of predation due to contextually learned associations between sound and prey. If seals quickly learn to associate pinging tags with food, so do other marine mammal species, including dolphins, fish-eating whales, and orcas. Though the tagging of marine mammals is much rarer, those animals with pinging tags are probably similarly at risk of being eaten by predators up the food chain, Amanda Stansbury, the study’s lead author, stated.
It didn’t take long for the seals to figure out the pattern.