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Study 2008-10 lot 3 Study for the revision of the plaice box

Published on: Sat, 22/05/2010 - 08:15
Table of Contents

    Did the plaice box work? Requested by the NSRAC the Commission will evaluate the effect of the plaice box and look at ways the performance of the plaice box could be improved if at all closed areas do work. The evaluation of the proposed changes to take long term economic, social and ecological effects on board.

    Why this study?

    Taking into account an opinion from the North Sea Regional Advisory Council, the Commission has decided to review the plaice box  in order to propose a revision of the plaice box.


    Evaluate the efficiency of the plaice box for the conservation of plaice and propose modifications of the closed areas to improve the positive effect on the conservation of plaice and other marine organisms


    This study has evaluated the effectiveness of the fisheries management measure known as the “Plaice Box” (PB). The study gives an inventory of existing information and collects new material on the effects of the PB on the conservation of plaice and the impact of the PB on various components of the commercial fishing fleets. Based on an analysis of key processes that affect the impact of the PB, modifications were explored to improve the positive effect on the conservation of plaice and other species of marine organisms, including catches and by-catches of other marketable fish. An economic assessment of the consequences of those modifications, in terms of their cost-effectiveness, and implications for profitability of the activity is presented. Finally, the data requirements for future evaluations of the effects of the PB on conservation is discussed.

    The PB regulation affected fisheries differentially. The fleets >221kW lost fishing grounds, while the exemption fleets benefited from a reduction in competition with larger vessels. The PB remains an important fishing area for the fleet of smaller vessel, especially beam trawlers fishing for shrimps  and the mixed flatfish fisheries are most active and are earning more than 70% inside the PB.

    Contrary to expectations, plaice stock biomass in the North Sea decreased from landings of 169 818t in 1989 to only 48 875t in 2008 undermining the credibility of closed areas as a fisheries management tool. The main question is whether the decrease in the plaice stock is due to the establishment of the PB or due to a change in the environment unrelated to the establishment of the PB (ocean climate, eutrophication, others).

    The level of protection offered by the PB has been far lower than was originally expected in 1989. This is due to the lower growth rate of plaice and the shift of undersized plaice to deeper waters outside the PB. Nevertheless, the proportion of undersized plaice relative to the marketable sized plaice is still higher in the PB than outside. The discard rate in the PB will be higher than outside.

    Given the original objective of the plaice box to reduce discarding of undersized plaice, re-opening of the plaice box is expected to lead to a small (<5%) increase in plaice discard numbers and decrease in yield and spawning stock biomass (<5%). Extending the PB to encompass one extra line of rectangles along the continental coast of the Netherlands would encompass 93%, 70% and 54% of age 0, 1, and 2 plaice respectively and will likely result in a moderate reduction in plaice discards (<10%) and moderate increase yield per recruit and spawning stock biomass (about 10%). Nevertheless any effects will be impossible to detect because of the variability in natural recruitment which we cannot measure accurately.

    Any change in management will impact the fleets differentially. Extending the PB will benefit the exemption fleets, while re-opening of the PB will benefit the fleet of large vessels and harm the exemption fleets. The shrimp fleet will be marginally affected by a change in the PB since they operate mainly within the 12 nm zone. Real time closure is expected to contribute to a reduction in plaice discarding. The effect can not be evaluated because of a lack of detailed data on the frequency, duration and spatial scale at which local concentrations occur.


    Full title: Study for the Revision of the plaice box

    Organisation: IMARES

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