Flirt or flight? How humans are scaring fish off finding a mate

By Jack Guy, CNN

(CNN) — Scientists studying squaretail grouper have found that the increasing presence of fishermen in the water is changing their behavior from flirty to flighty.

A team led by scientists at Lancaster University in the UK found that the fish are becoming more scared of humans and spending less time on courting behavior, with potentially important impacts on population levels, according to a statement from the university published Wednesday.

Study lead author Rucha Karkarey, senior research associate at Lancaster University, told CNN that researchers have been working at the same site in India’s Lakshadweep archipelago, north of the Maldives, for 10 years.

Around five years ago, the area started to be fished more intensively, and researchers began noticing more fearful behavior in the squaretail grouper around two years ago, said Karkarey.

This coincides with a shift from hook and line fishing from boats to fishers spearfishing while in the water, she said.

“Being fearful of predators is an evolutionary mechanism that helps animals survive predation,” said Karkarey.

“But now they’ve started recognising humans as predators,” she added. “It’s a natural response to an unnatural predator.”

This impacts reproduction due to the fact that groupers only reproduce at spawning events, when fish from a certain area congregate to find a mate at a specific location a handful of times per year.

Humans have responded to this behavior by targeting these events in order to catch more fish, which have started to engage less in courting behavior out of fear.

Interestingly, it is the fitter male fish who are most vulnerable to being caught, as they are more likely to engage in risky courting behavior to find a mate.

This includes defending a certain territory by refusing to cede it to a potential love rival, or a human fisher, or returning to a threatened territory more quickly than less fit male fish, explained Karkarey.

Unfortunately, female squaretail grouper select mates based on these qualities, which means that more fishing not only impacts the population by removing fitter fish from the sea, but also by reducing the ability of those left to reproduce as they are less fit as mates and more fearful of humans.

“Over the long term, not only are the fish declining because they are being fished, they’re also reproducing less and less at these events,” said Karkarey.

In many populations, these spawning events are the only time that groupers will mate, she added.

“It can have quite a huge repercussion for the population,” said Karkarey.

While other research has suggested that groupers can adapt to human interference by aggregating at different times or at different locations, Karkarey said that this has not been observed at this site.

Karkarey highlights the fact that fishing has intensified in recent years in the region.

“Fishing can have these really important indirect effects,” she said, adding that she hopes the study will act as a jumping off point for further research into how much fishing a squaretail grouper population can withstand without altering the behavior of the fish.

Karkarey also wants to investigate whether these fearful fish are finding other ways to mate despite the behavioral changes researchers have observed.

“What we really want to know is how they are impacting reproductive output,” she said.

The study was published in the journal Biology Letters.

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