Tagging fish can alert predators to their whereabouts

New research shows that the sound emitted by fish tags can make them more likely to become dinner for grey seals (Photo: University of St Andrews)

Tagging fish offers scientists new ways of learning about their movements, growth and methods of survival. While this helps in conservation efforts, new research suggests it may in fact be having an adverse effect, with the sounds emitted by the tags alerting predators to the fish's location and where to hunt for their next meal.

When these small tags are fixed to fish for research, they communicate their position to scientists by emitting a pinging sound. Looking to investigate whether this sound actually works to the fish's detriment, a team at Scotland's University of St Andrews conducted an experiment with grey seals acting as predators.

The researchers built a maze of 20 boxes, two of which contained fish – one tagged and one untagged. Across 20 trials, 10 grey seals were much quicker to zero in on the pinging fish and visited the tagged box more than any other, indicating that they were in fact responding to the scientific equipment.

"The seals found the tagged fish sooner and with less searching than the fish without a tag," says Amanda Stansbury of the university's Sea Mammal Research Unit. "This means that the seals learned to use the sound from the pinging tags to find where their food was hidden. This tells us that seals can exploit new sounds, such as fish tags, and use them to their advantage."

The scientists warned that fish tagging may be impacting on the accuracy of marine research. "“We expect that other marine mammals are similarly able to use such information to find prey," says Stansbury. "Tagged fish may be more detectable by predators, which could affect the results of fish studies."

The team's research was published in the journal Proceedings of the Royal Society B.

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