Tags on fish may act as 'dinner bell' for seals

November 19, 2014
A study revealed that seals are more quickly attracted to fish that have been attached with sound-emitting tags, creating a "dinner bell" effect on the seals

Sound-emitting tags fitted to fish to track their survival may, paradoxically, be alerting predator seals to their whereabouts, said scientists Wednesday who warned of a "dinner bell" effect.

Tests with captive grey seals showed that they learned quickly to associate the tag's sound with the presence of an easy meal, British researchers reported in the journal Proceedings of the Royal Society B.

Ten juvenile seals who had not been exposed to acoustic tags before, were put to the test in a concrete pool with twenty boxes into which , tagged and untagged, were randomly placed for them to eat in 20 trials.

"The seals found the tagged fish in fewer box visits than the untagged fish in later trials, demonstrating the learned use of the acoustic tag to locate food," the researchers found.

With each consecutive test, seals needed about five percent less time to find the box with the tag inside. And they visited the boxes with tagged fish much more frequently than empty boxes or those with non-tagged fish.

Acoustic tags are widely used in mark-and-recapture studies to assess fish survival and stock health. They produce ultrasonic frequencies thought to be imperceptible to the fish that carry them.

Previous studies had suggested the signal was audible to some predators, like seals, but this was the first research to find a "learned association between a signal and food leading to a 'dinner bell' effect," the authors said.

"Our results... illustrate the importance of considering the auditory sensitivities of all animals in the environment when designing an acoustic tagging study," they wrote.

"We showed that acoustic tags... aid prey detection, potentially increasing predation of tagged animals" and potentially skewing study findings.

The team said similar results were likely for other animal species and for other man-made sounds like boat engines, turbines and sonar—causing behaviour changes that could have profound effects on an ecosystem.

This may include tagged predators, like sharks, having less and less hunting success as and other prey scatter in front of the acoustic signal.

"Thus, when introducing artificial sound sources into an environment, it is important to take into consideration all potential effects on local species, both detrimental and beneficial," the authors said.

Explore further: Gray seals consume as much fish as the fishing industry catches

More information: Grey seals use anthropogenic signals from acoustic tags to locate fish: evidence from a simulated foraging task, rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2014.1595

Related Stories

Ningaloo snapper branches out of sanctuary zone

November 3, 2014

Spangled emperor (Lethrinus nebulosus) within the Ningaloo Marine Park have been found to move outside the sanctuary's boundary a year after being tagged—presenting possible implications for shoreline fishing rules.

Seals forage at offshore wind farms

July 21, 2014

By using sophisticated GPS tracking to monitor seals' every movement, researchers have shown for the first time that some individuals are repeatedly drawn to offshore wind farms and pipelines. Those man-made structures probably ...

Noise pollution impacts fish species differently

July 24, 2014

Acoustic disturbance has different effects on different species of fish, according to a new study from the Universities of Bristol and Exeter which tested fish anti-predator behaviour.

Silent stalkers of dark ocean waters

December 3, 2013

The mating roar of a male harbor seal is supposed to attract a partner, not a predator. Unfortunately for the seals, scientists have found evidence that marine-mammal-eating killer whales eavesdrop on their prey. The researchers ...

As numbers of gray seals rise, so do conflicts

July 20, 2014

(AP)—Decades after gray seals were all but wiped out in New England waters, the population has rebounded so much that some frustrated residents are calling for a controlled hunt.

Recommended for you

Rethinking role of viruses in coral reef ecosystems

May 22, 2017

Conventional wisdom has it that within virus-bacteria population dynamics, viruses frequently kill their host bacterial cells—a process called lysis—especially when there's a large concentration of bacteria. A different ...

New clues emerge about how fruit flies navigate their world

May 22, 2017

Nestled deep inside a fruit fly's brain, specialized nerve cells knit themselves into a tiny compass. New results from neuroscientists at the Janelia Research Campus illuminate the architecture of this circuit and the neural ...

New findings on formation and malformation of blood vessels

May 22, 2017

In diseases like cancer, diabetes, rheumatism and stroke, a disorder develops in the blood vessels that exacerbates the condition and obstructs treatment. Researchers at Karolinska Institutet now show how blood vessels can ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

Kedas
not rated yet Nov 19, 2014
How does the seal know it comes from a fish that they can eat or from a shark that will eat them?

anyway, if you are tagged you are the black sheep in the group.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.