Title: Sustainable Management of Mixed Demersal Fisheries in the North Sea through Fleet-based Management - a Proposal from a Biological Perspective
Authors: RÄTZ Hans-JoachimBETHKE EckhardDOERNER HENDRIKBEARE DouglasGRÖGER Joachim
Citation: ICES JOURNAL OF MARINE SCIENCE vol. 64 p. 652-660
Publication Year: 2007
JRC N°: JRC33755
URI: http://publications.jrc.ec.europa.eu/repository/handle/JRC33755
Type: Articles in Journals
Abstract: Cod, haddock, whiting, saithe, plaice, sole and Norway lobster are the 7 main target species of the mixed demersal fisheries of the North Sea, Skagerrak and Eastern Channel. Among these, cod and plaice stocks are at low levels (historically), there is risk of poor recruitment and the current levels imply ongoing and significant losses in long-term yields. The 7 main resources are exploited by a variety of competing fleets deploying often quite unselective gears. The poorly defined fishing strategies result in high discards or unallocated landings far in excess of the single species TACs and thus jeopardizing multi-annual recovery and management plans. In this paper we propose a fleet specific effort management system. The fleet specific effects we estimate are based on the sum of partial exploitation rates of the species caught. They are then weighted by the ratio of the actual SSB size and the precautionary biomass reference (Bpa) which is also the ‘ecological quality objective’. As an axiom, fishing activities are thus considered more beneficial with decreasing numbers of species represented in the catch. The developed relative effort factors were applied in medium term simulations of the annual management decision processes on future catch possibilities, in accordance with the existing or proposed multi-annual management plans (including the cod recovery). Uncertainties in the international catch data compiled and the stock assessments significantly undermine the results and their application for management purposes. Towed nets, including seines equipped with 70-99 mm or ≥100 mm mesh size, beam trawlers ≥ 80 mm and gill nets are identified as the main gears affecting the depleted cod and plaice stocks. In contrast, trawls of 16-31 mm, longlines and other gear types appear to less significantly affect the stocks we considered. The proposed fleet management would require stringent effort reductions for the cod and plaice sensitive fleets over a time period of about 5 years, i.e. towed nets of ≥100 mm mesh size, beam trawlers ≥ 80 mm, trawls of 70-99 mm and gill nets. This will reduce the exploitation rates of all stocks significantly and, after their recoveries, catches will continuously exceed recent levels by far and management interventions would be minor. The more selective longlines and other fleet types will profit from increased effort and catch allowances over the entire scenario periods. The recovery and management plans on cod are dominating the management decisions resulting in significant under-exploitation of each haddock, saithe and plaice stocks due to poor fishing strategies with high by-catches. Even a low degree of non-compliance with the effort and adapted catch allowances as simulated through parameter bias indicates significant delays in realizing the predefined management goals.
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