Technical approaches to avoid cod catches in Baltic Sea trawl fisheries : A report for the BALTFISH high level group
In the last few years, the Thünen Institute of Baltic Sea Fisheries developed and tested several selectivity devices for demersal trawls with the aim to reduce the unwanted bycatch of Baltic cod, while maintaining the high catchability of flatfish. This research is a direct response to the poorstatus of both Baltic cod stocks(ICES, 2019a, 2019b), resulting in reduced catch opportunities (Western Baltic cod) or a closure of the directed fishery (Eastern Baltic cod), respectively.to ad-hoc measures to alleviate a serious threat to the conservation of eastern Baltic cod, im-plemented by the European Commission by July 22, 2019(EU 2019/1248). The presented workup dates and complements the ICES report on ‘Technical strategies to avoid catches in the Baltic Sea trawl fisheries’ (ICES, 2019c). There is now (April 2020) much knowledge gained compared to the state of play in the ICES report. This can now be considered state-of-the-art technology. Since September 2019, two different approaches and a combination of the two were investigated: 1. modifications of the extensions and 2. modifications of the codend. For approach 1., the following selectivity devices were (further) developed and tested(Figure 1): (1)CODEX (COD EXcluder): A guiding panel in the extension of a trawl guides cod towards an escape opening. (2)ROOFLESS (in various configurations): The top panel of the trawl extension was removed to build a large escape opening (175cm, or330cm long). Additionally, configurations with stimulation ropes (STIPED) were tested. Both devices were mounted in a standardized 4-panel extension of the trawl, developed at the Thünen Institute (NEMOS, NEt Enabling MOdular Selectivity, Figure 3) to ensure a firm shape of the extension and hence reduce variability in the efficiency of the selection process. The experimental work was conducted during four cruises between September 2019 and February 2020. For CODEX, it was shown that cod catches could be reduced significantly, but also flatfish catches were reduced largely. The different ROOFLESS-configurations have also shown very good capabilities to reduce the bycatch of cod, while the catch efficiency was higher for flatfish species compared to CODEX...