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Tags on fish could be creating a "dinner-bell" effect for predators

A study has found that grey seals have an easier time locating tagged fish, raising concerns about how this scientific tool may impact some populations.

Amanda Stansbury

Those pinging tags scientists use to track and study fish may also be proving predators an acoustic roadmap to find them.

Testing the theory on grey seals which are known to use sound to their advantage, marine biologist at the University of St. Andrews in Scotland set up a maze of boxes in a swimming pool. Two of the boxes contained a fish - one with a pinging tag and the other without.

"The seals found the tagged fish sooner and with less searching than the fish without a tag," said Amanda Stansbury, who with Thomas Gotz, Volker Deecke and Vincent Janik carried out the research at the University of St. Andrews 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," she said. "This tells us that seals can exploit new sounds, such as fish tags, and use them to their advantage."

The study in the Royal Society journal Proceedings of the Royal Society B Wednesday show that the affects of noise in the sea "can be complicated" and that scientists may want to think twice in the future before they tag certain types of fish. The researchers conducted 20 randomized trials using 10 seals.

"All tagging studies rely on the basic assumption that tags have no significant impact on marked individuals," the researchers wrote in the study. "However, our results suggest that acoustic tags could have profound effects on the fitness of the studied individuals in situations where they are audible to conspecifics, predators or prey."

Stansbury said their findings could have implications for "other predators" and said she felt more sedentary fish would be more vulnerable to the pinging tags than those that are fast moving.

"Tagged fish may be more detectable by predators, which could affect the results of fish studies," she said. "When we make noise in the sea, we need to consider how animals are affected. Our results show that such effects can be complicated. In our case they were beneficial to the seal but bad for the fish."

  • Michael Casey

    Michael Casey covers the environment, science and technology for CBSNews.com