Bycatch is a serious conservation issue for many vulnerable seabird species and solutions are often lacking. A new paper published today explains a new mitigation technique which could help. Birdlife’s Bycatch Programme Manager Yann Rouxel and RSPB Conservation Scientist Steffen Oppel explain.
Many seabirds eat fish or molluscs, and they are very good at diving after and catching them in the sea. However, when they chase their prey under water, they generally focus on catching them, and not so much on avoiding obstacles. That wasn’t a problem until humans invented nets to catch fish – and now inadvertently catch lots of seabirds in the same nets.
Globally, hundreds of thousands of seabirds get accidentally caught in fishing nets and drown every year. To try solve this conservation issue, the RSPB has worked with BirdLife partners in several countries for many years to develop solutions how to reduce seabird bycatch in static fishing nets – but so far no solution has been found. However, in 2021 we conducted a promising trial with a buoy that might repel birds from foraging near fishing nets, so we proceeded to test this device in a fishery affected by this issue; the Icelandic Lumpfish “caviar” fishery.
Looming-eyes Buoys (LEB) deployed in the Küdema bay, Saaremaa, Estonia (c) Ainar Unus
Study results
In a new study published today, Yann Rouxel and colleagues report the somewhat deflating results of this test – attaching the buoys with looming eyes to fishing nets in Iceland did not reduce the bycatch of seabirds. The species most frequently caught in the fishery in Iceland, seaducks and guillemots, were caught in similar proportions in nets with or without the looming eye buoys.
However, while analysing the data the RSPB team discovered that most of the seabirds were actually caught in relatively shallow waters. Fishermen who set the nets in deeper waters generally returned without having caught (m)any birds.
Given that a simple techno-fix (the looming eye buoy) did not appear to be a promising solution, the RSPB team then simulated what would happen if the fishery was simply asked to fish in slightly deeper waters.
By carefully reallocating some of the fishing effort from shallower to deeper waters, they found that the fish catch could be maintained but the bycatch could be virtually eliminated if the fishery would be restricted to fish in waters from 50m and deeper.
Impact on seabirds
This simple measure could reduce the annual death toll of the Icelandic Lumpfish fishery alone, from currently between 5,000-9,000 seabirds every year to almost no seabird bycatch at all.
This measure would be particularly helpful for the Black Guillemot population of Iceland, currently listed as Endangered, and – if our analysis is correct - could reverse the population decline observed for this species in the last decades.
Black Guillemot in Scotland (c) Ben Andrew (rspb-images.com)
While requiring further research, properly established depth-based measures are also expected to reduce the bycatch of marine mammals, in particular seals. Although we predicted that fishermen could catch the same amount of fish in deeper waters with the same effort, more work is required to understand the socio-economic consequences of such a measure.
Nonetheless, for this particular fishery there is at least some hope that a relatively simple management measure could allow seabirds to once again dive freely in pursuit of fish without the significant risk of being caught in nets.
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