MSC certification of the plaice fishery in area IIIa – basic investigations and development of a management model (39025)

A management plan is an important requirement for MSC certification of specific fisheries. However,prior to this project, reliable stock assessments, which are necessary for a management plan for plaice (Pleuronectes platessa) in area IIIa (Kattegat/Skagerrak), had not been available. These problems most likely originated from insufficient knowledge about the geographical distribution of populations as well as the interactions between populations in Kattegat/Skagerrak and neighbouring areas. 
Through a mapping ofthe distribution and dynamics of populations, this project aimed at providing the missing data that would ultimately allow for the development of a management plan for the plaice fishery in area IIIa. The work included information from genetics, tagging, otolith based growth estimation,oceanographic modelling and analyses of survey and fisheries data. 
Results from the project showed evidence of both local population components in the Kattegat/Skagerrak as well as substantial mixing between North Sea population and these local components, and consequences of lumping or splitting the populations for stock assessment and management were discussed. 
The outcomes of the work directly influenced the policy decisions since 2015. Decision was finally made to proceed with the lumping option, thus allowing a quantitative analytical assessment and management advice for the area. However, because of the differences in size between the two populations, there is a risk of depletion of the local Skagerrak population if the fisheries on it increase as a consequence of the increase in the North Sea stock. In terms of management,some mechanisms already exist for reducing the fishing pressure in the Skagerrak if deemed necessary, as plaice in the North Sea and in the Skagerra kare managed by two different Total Allowable Catches (TACs). It has therefore been suggested that routine monitoring of the survey and fisheries patterns would allow detecting any departures from the current situation, i.e. a decoupling of trends in the different areas and the different seasons that could indicate a reduced productivity of the local stock. 
In the longer-term,the current progresses on the biological knowledge of the stock in Skagerrak should be sustained. Additional genetic allocation of individual fish to the different populations should be performed to obtain a better quantification of the mixing in different areas and seasons, and the survey coverage should be improved in the Skagerrak.
The project was coordinated by DTU Aqua and funded by the Danish Ministry of Food, Agriculture and Fisheries and the European Fisheries Fund (EFF).
Research area: Population GeneticsResearch area: Fisheries ManagementResearch area: Marine Living Resources