Scientists in the Western Baltic Sea tried to find a way to deter birds from stealing fish from nets and soon found that their clever solution wouldn’t last for long.
Birds such as great cormorants and gulls can cause problems for fisheries and aquaculture facilities because they swoop into nets and steal the readily available fish for dinner.
This can affect fish populations, reduce fisheries’ profits and can even be harmful to the birds if they get entangled in the nets or are shot by fishers trying to keep them away from their catch.
Researchers wanted to find a way of protecting the fish that wouldn’t impact seabird populations – so they painted eyes on windmills to try to scare them away. It worked – at first – but keeping the hungry birds away wouldn’t last for long. The findings are published in Royal Society Open Science.
“In the Western Baltic, large fixed traps (pound nets) are used to target migrating fish. These gears attract piscivorous seabirds that feed on the trapped fish,” write the authors in the study. “We tested the Looming-Eye Buoy (LEB), a floating windmill with a pair of eyes printed on the wings, intended to produce an aversive effect by mimicking the approach of a predator.”
Pound nets work by using wooden poles and mesh panels to channel fish shoals into an enclosure with a trap at the end, which is regularly emptied by fishers. “These poles and the nets that protrude from the surface in between often serve as perching elements for coastal piscivorous seabirds,” write the authors. “These birds typically take advantage of the large fish concentrations inside the trap to feed on them.”
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According to the study, great cormorants, greater black-backed gulls, lesser black-backed gulls and herring gulls are all commonly found pinching fish from these nets. “With generally several dozens of birds continuously present in and around each fish trap, the potential economic loss for pound net owners can be important,” write the authors.
To keep the birds away from their catch, fishers have tried covering the traps with netting or creating hiding places for the fish but these didn’t work. “Great cormorants managed to enter the pound net underwater from the heart when a protective net was covering the chamber,” they say. While building small chambers inside the pound net did prevent the birds from getting to the fish, it increased their chances of getting tangled in the gear and drowning.
To test a different approach, the scientists created a ‘Looming-Eye Buoy’ – or LEB – to try to scare the birds away.
“The LEB consists of a small floating windmill with sketches of eye shapes of different sizes printed on each side of the wings,” they write. “While the wind pushes the wings, the rapid alternation of eye sizes supposedly produces the impression of a looming predator on the viewing birds, making them avoid or flee the area.”
Initially, it seemed to work – four days after installing the LEB, almost four times as many seabirds were observed at the control site than the location with the googly-eye device.
But the effect didn’t last long. “On the last day of the trial (day 46), however, the difference was no longer significant,” write the study authors, suggesting that the bold birds quickly got used to the spooky peepers and were no longer put off by their gaze.
“Approximately a month after LEB implementation, all the bird groups considered here had habituated to the device,” write the authors, “and the frightening effect of the LEB on piscivorous seabirds was not visible anymore.”
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