Crafty Seals Seek Follow Tracking Device Signals To Catch Fish

Tiny monitoring devices have become an increasingly common way for scientists to study elusive animals that are difficult to track on a day-to-day basis. However, now it seems that smart seals have caught on to the trick and are using it to their advantage to catch fish!

This stunning finding was revealed in a study published on November 19th, in the Proceedings of the Royal Society B by a team of researchers from the University of St. Andrews in Scotland. The scientists decided to embark on the investigation after previous research indicated that while ultrasonic frequencies produced by acoustic tags (the kind used in fish) were imperceptible to the animals they were being used on, predators like seals and sea lions were able to detect the signal quite easily.

To verify if that was true, the scientists selected a group of ten juvenile grey seals that had been born in captivity. This meant that the marine animals had never encountered the ocean, nor been exposed to any kind of acoustic tags. The researchers then placed the seals one at a time, inside a pool that contained 20 foraging boxes, only two of which housed fish - one with tags and the other without.

Each seal was allowed to explore the boxes twenty separate times. In order to ensure that mammal was not depending on its memory, the fish were randomly moved to different boxes, each time. At first, there was no difference in the amount of time it took the seals to discover the tagged and untagged fish. However, after they had been in the pool a few times, they started locating the tagged fish much faster. What was even more interesting is that the more 'experienced' they got, the faster it took them to find their prey. Not surprisingly, the frequency of visits to the box with the tagged fish also increased with each trial. This led the researchers to conclude that the seals had figured out how to use the acoustic signals to their advantage.

To confirm that this indeed was the case, the researchers conducted a second experiment using two boxes - one with pieces of fish and the other with just acoustic tags. Sure enough, the seals all gravitated to the one that was emitting signals.

While this experiment involved only seals, the researchers believe that other marine mammals may also be using the information to catch prey. Inversely, predators like sharks that have been tagged by scientists may be negatively impacted, as pings they emit could warn their prey of their presence. Besides potentially messing up nature's food chain, the 'dinner bell' effect of the acoustic tags could also mean that the conclusions reached by previous fish studies may be biased. Now that the secret is out, scientists will have come up with another innovative way to conduct their studies - one that is not detectable by the crafty marine animals.

Resources: IFLscience, standrews.ac.uk, newscientist.com