Report on eastern Baltic cod bycatch in non-targeted fisheries, mixing with western Baltic cod in SD24, and stock situation in SDs 27-32
reportposted on 2020-01-01, 00:00 authored by ICESICES
1. Bycatch of Eastern Baltic cod in non-targeted fisheries 1a.Total cod bycatch in 2018 was in the range of 360-1306 * tonnes in subdivisions 25-32 (eastern stock) and 66-417* tonnes in subdivision 24 (eastern and western stock combined). The ranges correspond to different bycatch thresholds from 10 to 50% cod in the landings in a fishing trip. These cod bycatch amounts correspond to fishing patterns in 2018 when cod was a target species, and fishers did not attempt to avoid catching cod. 1b. Bycatch of cod in demersal trawl fisheries for flatfish could be substantially reduced when applying selectivity devices in fishing gear. Three selectivity strategies are possible: i) species specific size selection, ii) selection by behavioural differences of the species and iii) a strategy that combines i and ii. Strategy i can be efficient to reduce bycatch of small but not larger cod, while strategies ii and iii can be applied to minimise bycatches of cod at all sizes in targeted flatfish fisheries.1c. Cod and flounder overlap in the entire distribution area of the eastern Baltic cod stock; plaice and eastern Baltic cod overlap in subdivisions 24-25. Therefore, there are no areas or months where flatfish fisheries with non-selective gears could be conducted in subdivisions 24-26 without a risk of bycatch of cod. Only a small fraction of EU flatfish landings were taken in subdivision 26 in later years (6% of flounder landings in 2018). Therefore, a potential closure of subdivision 26 for demersal fisheries would have limited implications for EU flatfish fisheries, while protecting a substantial part of the eastern Baltic cod stock. 2. Mixing of eastern and western Baltic cod in subdivision 24 2a. Eastern Baltic cod (EBC) occurs throughout subdivision 24 and in all seasons. However, the proportion of EBC is lowest: (i) in the area west of 13°E (on average 47% EBC in last 11 years), compared to the area east of 13°E (on average 78% EBC) and (ii) in waters between 0-10m or 0- 20m deep (on average 27% or 39% EBC, respectively). The latter is assumed not to include the coastal waters around Bornholm Island. The proportion of eastern Baltic cod is lower in fisheries by passive gears due to their use mostly in shallow areas. 2b. Bycatch of eastern Baltic cod in fisheries targeting western Baltic cod can be calculated by multiplying the TAC for the management area with the fraction of it taken in subdivision 24 (0.53 in the last 3 years) and the proportion of cod in subdivision 24 that belongs to the eastern stock (0.74 in the last 3 years). The additional fishing restrictions applied in 2020 in subdivision 24 are expected to reduce the fraction of the cod TAC taken in subdivision 24, and thus reduce the bycatch of eastern Baltic cod. 2c. A closure of subdivision 24 could result in up to 25% loss of western Baltic cod commercial landings, at the fishing patterns observed in latest years. It is difficult to foresee to what extent effort reallocation to subdivisions 22-23 would be possible for different fleets. The cod TAC at 3806 tonnes set for the western Baltic management area for 2020 is close to the amount that has been taken in subdivisions 22-23 in later years. Thus, the TAC at 3806 tonnes would likely be possible to take in subdivisions 22-23. 3. Cod in subdivisions 27-32 3a. Eastern Baltic cod annual catches in subdivisions 27-32 were between 150-400 tonnes in 2010- 2018, with the exception of 2017 (883 tonnes). This corresponds to less than 1% of the total catch from the eastern Baltic cod stock in these years, with the exception of 3% in 2017. Most catches within this area were taken in subdivisions 27-29, both by active (trawls) and passive (gillnets) gears. 3b. Fishing at status quo effort in subdivisions 27-32, corresponding to total cod catch of 168 tonnes in 2020, is estimated to result in 0.08 % lower SSB in 2021 compared to the scenario of zero catch. 3c. Potential effort reallocation to subdivisions 27-32 could result in removing up to 3% of the total biomass of the eastern Baltic cod stock.
Published under the auspices of the following ICES Steering Group or Committee