[ EVENTS ] Workshop on technical solutions to reduce cod bycatches in the Baltic, 30 November 2020
Innovative modifications to existing gears Thuenen Institute
Thuenen Institute
Cod is one of the most commercially important species in the Baltic Sea providing a livelihood to fishers from countries across the region. Arresting the steady deterioration in the state of cod stocks calls for a slate of measures. Adapting fishing gear is one of them.
The Bacoma codend has a standard mesh with a square mesh panel on the top section of the codend and is a standard fishing gear in the Baltic.
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here are two cod stocks in the Baltic the eastern Baltic cod and the western Baltic stock. For several reasons, many of them related to the environment, the eastern Baltic stock is in particularly poor condition and ICES, the international body that assesses these stocks, has estimated that the stock is below safe biological limits and that it will remain so in the medium term even if it is not fished at all. According to ICES, the stock has further declined since last year and the organisation therefore advised zero catches in 2021. This however would choke fisheries where cod is caught as a bycatch. Based on an updated ICES assessment of levels of cod bycatches in other fisheries, the Commission elected to limit the TAC for eastern Baltic cod to unavoidable bycatches. The TAC for bycatch which was reduced by 92 to 2,000 tonnes in 2020 has been further reduced to 600 tonnes in 2021.
Baltic Sea Advisory Council, Baltfish, and DTU Aqua collaborate on fishing gear workshop The state of the cod stock thus impacts cod fishers as well as fishers targeting species where cod is a bycatch. At the end of November, the Baltic Sea Advisory Council, Baltfish, and DTU Aqua jointly hosted a virtual workshop to discuss technical solutions to reduce unwanted catches of cod in the Baltic Sea fisheries. The results of the discussion would feed into a Baltfish joint recommendation for more selective gear that would target flatfish and minimise bycatches of cod, said Estonia’s Kaire Märtin, the chairperson of Baltfish. She also expressed the hope that the meeting would result in suggestions to streamline the process of developing and implementing new or improved gear solutions. Scientists studying the eastern Baltic cod stock have noted that today natural mortality is six times
higher than fishing mortality, a highly unusual condition as most cod stocks exhibit the reverse. The fish since about 1990 have become smaller, skinnier, and also mature when they are smaller, meaning that the volume of roe (the number of eggs) is also less compared with fish that mature when they are larger. Marie Storr-Paulsen, a researcher at DTU-Aqua attributes these developments to a lack of oxygen, less prey for the fish to feed on, and an increased seal population. Studies of the oxygen levels in the Baltic Sea show that the area with little or no oxygen has increased over the years. Part of this is due to the inflow of the nutrients, nitrogen and phosphorus respectively from agriculture and from municipalities. Although this has declined significantly since peaking in the 80s, it may not be reflected in higher oxygen levels in the water as oxygen depletion is measured at the sea floor. Another complication is the climate change influenced rise in water temperature which increases the fish’s demand for oxygen.
Studying cod prey revealed that the number of a certain crustacean (Saduria entomon) in stomachs of large cod had declined drastically since 1994 compared with before the 90s, probably because the crustacean could not tolerate the low oxygen conditions at the sea bottom. The distribution of sprat, a fish on which cod feed, has also changed so that there is now little overlap between the two species. Grey seal abundance in the Baltic Sea has increased steadily since 2003. The seals prey on the cod, but another more serious impact comes from playing host to a parasite that attacks cod livers which in turn influences the growth of the fish. Studies have shown that the number of parasites per fish in the eastern Baltic is considerably higher than in the western Baltic. As a result of these factors, conditions for cod have become less favourable over time contributing to the phenomenon we see today of undersized fish and unhealthy stocks. Various measures have been taken to reduce pressure on
