Acoustic tags on fish may act as dinner bell for seals
According to a recent study published last week, grey seals use the anthropogenic signals from acoustic tags to locate fish.
Scientists place acoustics tags on fish to study their behaviour and movement. These tags emit ultrasonic frequencies which marine mammals are able to detect.
The study available in the Royal Society journal Proceedings of the Royal Society B, simulated a foraging task. 10 captive grey seals with no previous experience of associating sound with food were introduced to 20 different foraging boxes over 20 different trials. One box contained an acoustically tagged fish, one box contained an untagged fish, with all remaining boxes being empty.
Results showed that seals revisited boxes containing the tag significantly more often than any other box. This tells us that seals are capable of not just detecting, but also exploiting new sounds and using them to their advantage.
Over the course of the trials, the foraging time and number of boxes visit considerably decline. In other words, the seals became quicker at finding the box containing the tagged fish. The seals quickly learned to associate the sound of the pinging tags with the presence of food. This indicates the learned use of the acoustic tag to pinpoint food.
The authors describe a “dinner bell” effect for the seals. The pinging tags are acting as a bell just like they’re being called to dinner.
Tagged fish may be more susceptible to predation. The recent finding may have a profound effect on research intended to monitor fish stocks. There is already evidence for decreased survival rates for acoustically tagged juvenile salmon. With the increase in the use of acoustic tags in mark-recapture studies to measure fish survival this may lead to inaccurate conclusions.
Photo credit: Wildlife Insight
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