Seabird bycatch: new research on gillnet fisheries in the Baltic Sea
Television viewers have recently had a wealth of opportunities to learn about the diversity of life in our seas, most notably courtesy of Sir David Attenborough. They’ve also had the less palatable chance to see some of the ever-increasing range and severity of threats to this abundant life. We’ve seen a fair bit about the threats to marine mammals, sharks and turtles from fishing activities, both intentional and unintentional, in terms of overfishing, entanglement in ‘ghost gear’ but also so called ‘bycatch’.
Bycatch can be defined as the unintentional capture of non-target species in fishing gear. This is a worldwide problem, from albatrosses and petrels caught on longline hooks set to tuna, to turtles and porpoises caught in drift nets, and right whales tangled in lobster pot lines. One area that sees less publicity, but also takes a huge toll, are the gillnet fisheries around the world, and notably in the Baltic Sea. The Baltic Sea is a large and economically important body of water, supporting many international transport links as well as industrial and artisanal fisheries. The history of its fisheries is long and deeply entwined in the culture of coastal communities – with annual smelt festivals in Russia, Latvia and Lithuania to name but three.
However, the Baltic Sea is also an extremely important area for a wide range of seabirds. For sea ducks in particular, such as the globally threatened Velvet Scoters, Long Tailed Ducks, and Steller’s eiders, the Baltic Sea is an extremely important wintering area, but also a dangerous place. Numbers of sea ducks in the Baltic have declined by over 50% in the last 20 years, and the numbers of these birds accidentally caught in coastal gillnets is thought to contribute significantly to these declines. Indeed, it has been estimated that around 76,000 seabirds are bycaught by gillnets in the Baltic Sea each year.
Long-tailed ducks at sea, photo by Julius Morkūnas.
Gillnets are long underwater walls of near invisible monofilament nylon nets, many hundreds of metres long, set to catch fish like smelt, cod, flounder and salmon. They are very efficient at catching fish, but also other things. In the shallow coastal waters of the Baltic states, there are thousands of small boats using these nets in winter. Alongside this, they catch significant numbers of sea ducks.
There has been much effort to devise ways to prevent bycatch of many different sorts of animals in different fishing gear. Mitigating seabird bycatch in longline fisheries has been proven possible due to ingenious but basic devices, such as Bird Scaring Lines, reducing bycatch of albatrosses on longlines by more than 90% in some fisheries (as our Albatross Task Force have demonstrated). For gillnets, acoustic ‘pingers’ and LED lights have shown promising results in deterring sea mammals and turtles (respectively), however, much less is known about how to prevent seabirds getting caught in gillnets.
Bycaught Velvet Scoter, photo by Julius Morkūnas.
A paper recently published in the journal Global ecology and conservation presents some recent work conducted in the coastal fisheries of the Baltic Sea. Alongside the Lithuanian Ornithological Society and the Polish National Marine Fisheries Research Institute, the Royal Society for the Protection of Birds and BirdLife International conducted collaborative work with Lithuanian and Polish inshore fishers to test potential solutions to seabird bycatch. In this paper, we detail how we tried three different net modifications to reduce the number of seabirds getting caught in nets from commercial fishers. Based on a collaboration with avian sensory ecologists, the Fishtek Marine engineering company, as well as previous field work in Peru, we tested small black and white striped panels, green LED lights and flashing white LED lights. Unfortunately, none of these three resulted in fewer seabirds being caught, contrary to evidence from Peru that green lights on the top of nets reduced the numbers of Guanay cormorants caught. We found no such difference where ducks are the birds being accidentally caught. More worryingly, using white flashing lights or black and white panels not only did not deter ducks from nets, but increased the numbers of Long-tailed ducks being accidentally caught. We think this attraction response may be something to do with the importance of black and white contrast to this species, which is itself displays a striking black and white plumage. Needless to say, though, none of these techniques seem to be suitable as deterrents to keep these birds away from fishing gear.
The problem, therefore remains an intractable one. Various other things could be tried, from preventing the conflict between fishers and birds in either time or space by closing areas to fishing at certain times. However, this seems unlikely to be acceptable to fishers or the economies they support. Other options, such as preventing seabirds diving in the vicinity of nets using deterrents, or using different types of lights, net materials, or even acoustic methods could be tried, but until we know more of the effects of these on the fish catch, or the birds’ behaviours, trials will have to continue. It seems unnecessary to say that with the scale of declines the urgency remains high. This study also highlights the need to be able to publish negative results (not always an easy task) to enable rapid refocussing of effort and resources away from unfruitful avenues of research.
Reference: Field, R., Crawford, R., Enever, R., Linkowski, T., Martin, G., Morkūnas, J., Morkūnė, R., Rouxel, Y., Oppel, S., High contrast panels and lights do not reduce bird bycatch in Baltic Sea gillnet fisheries, Global Ecology and Conservation (2019), doi: https://doi.org/10.1016/j.gecco.2019.e00602
Sincere thanks are due to all the fishers who participated in trials in Lithuania and Poland, without whom this research would not have been possible. Gratefully received funding from Fondation Segre and the Baltic Conservation Foundation allowed us to carry out this work in Lithuania; funding for the Polish work came from the European Union under an Executive Agency for Small and Medium Enterprises contract (EASME/EMFF/2015/184.108.40.206/SI2.719535).