Science1 publisher2 min readPublished
Bird-of-prey kites and spinning eye buoys cut seabird bycatch in Cornish gillnets by about two-thirds
Fishtek Marine's two-year trial with 10 Cornish gillnet fishers found the Looming Eye Buoy cut seabird catch risk by 59% and a bird-of-prey kite by 71%. Both were tested on working boats, giving gillnet fleets a field-tested option for gear the RSPB says has resisted bycatch fixes.
The Scientist · Science desk
What happened
- Gillnets around Europe's coasts are estimated to catch and drown about 95,000 diving seabirds, such as guillemots and razorbills, every year.
- The Looming Eye Buoy has a spinning head with an animated eye effect meant to scare birds away from diving into the nets.
- It was tested off Cornwall alongside the 'scarybird', a commercially available kite shaped like a bird of prey.
- Most of the seabirds caught in the Cornish trial were taken during the winter months.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- decision Because bycatch concentrated in particular months and places, managers can deploy deterrents only where and when birds are being caught. That cuts the number of devices a fleet has to buy and maintain.
- cost No price has been published for either device, so fleets and funders cannot yet work out a cost per bird saved. The kite being an off-the-shelf product is the only cost signal on record.
- constraint The evidence covers 10 boats in one county over two years. Applying a two-thirds cut to the Europe-wide 95,000 estimate goes beyond what the trial measured.
- precedent The RSPB says lessons from its worldwide rollout of bird-scaring lines are now being applied to UK seabirds, so gillnet deterrents are likely to get the same push from trials into regular fleet use.
Both percentages are cuts in the chance that a guillemot or razorbill ends up in a net [6]. Put the other way round, a net fished with the buoy kept about 41% of its unprotected risk, and one fished with the kite about 29% [1]. The two results average 65% [2], close to the "around two-thirds" the researchers give for both devices [6]. The kite finished 12 percentage points ahead [4]. I'd treat that ranking as open until the full paper shows how much uncertainty surrounds each figure.
The thing this doesn't tell you is the denominator. The published account of the study does not report how many birds were caught, how many net sets the cameras watched, or whether fish catches changed.
The counts came from cameras fitted to the fishers' boats [8]. Fishtek Marine led the fieldwork [7] and co-developed the buoy with the RSPB [2], out of an eight-year collaboration between the two [13]. The data were analysed by scientists at the University of Exeter, and the paper appears in Conservation Letters [5].
"This study provides some of the strongest evidence to date that simple, practical deterrents can substantially reduce seabird bycatch in gillnet fisheries," said Tom Horton, the Exeter lead author [10]. Tom Hooper, senior fisheries scientist at Fishtek Marine, said the fishers' involvement fed back into the hardware: "any technology used at sea must be simple and robust, so working with fishermen means that we learned a great deal about how the devices were used." [12]
Other gear has done better. Bird-scaring lines, which the RSPB helped deploy, cut bycatch by 98% on Namibian longliners and 95% on South African trawlers [14]. Those fleets were left with 2% and 5% of their former bycatch, against 29% to 41% in the Cornish nets [3][1]. The figures come from different fisheries, so the comparison is rough. Yann Rouxel, bycatch programme manager at the RSPB, said gillnets "have proved a real challenge to develop mitigation methods for and pose a significant threat to seabirds in the U.K." [15]
What to watch
- The full Conservation Letters paper's bird counts and uncertainty ranges, which would show whether the kite's 12-point lead over the buoy holds up.
- Trials outside Cornwall or longer than two years, to test whether the reductions hold in other gillnet fisheries.
- Any decision by UK fisheries managers to require or fund seasonal deterrent use in gillnet fleets.