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Investigations Into Closed Area Management of the North Sea Cod

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Investigations Into Closed Area Management of the North Sea Cod The Centre for Environment, Fisheries & Aquaculture Science Investigations into closed area management of the North Sea cod for Department for Environment, Food and Rural Affairs Defra Reference: SFCD15 CEFAS Contract report C2465 INVESTIGATIONS INTO CLOSED AREA MANAGEMENT OF THE NORTH SEA COD Cefas Reference C2465 Defra reference SFCD ref 15 Closed areas have been proposed as one of a range of potential management approaches that could be applied to control the exploitation rate of the North Sea cod stock. However, although theoretical studies of the potential effects of closed area are numerous, they are of limited use for providing practical management advice, because they are not case-specific. The aim of this project was to bring together fishers’ knowledge of current and potential future North Sea fleet fishing activity with research on the spatial movement of fleets, cod population biology and the impact of fishing on benthic biodiversity, in order to provide practical advice on the impact of closed area management in the North Sea. Research is required to aid the provision of advice on the potential impact of closed area management on cod population dynamics, habitat diversity and the economics of the North Sea fleets. Examples of closed area management regimes for the North Sea cod were simulated, and the impact on the catches of cod, mixed gadoids and benthic productivity and diversity was evaluated. Funding and the time available for the study was limited, so the work examined three example scenarios: two evaluating the impact of large, broad-scale, North Sea closures, and at a more detailed scale, the effect of a local closure on the cod fishery off the northeast coast of England. The outcome of the predicted changes in the dynamics of North Sea fleet effort distributions on the benthos and the cod stock is described. Conclusions are drawn with respect to the potential impact of the closures, including comparisons with other management actions or technical measures that could be employed to manage the stock; the design of closed areas for restricting access to stocks; and the effectiveness of the modelling approaches. The research has led to improved understanding of the potential impact that closed areas could have on the English and international fleet yields and the population dynamics of cod, especially recovery rates to biological reference points. The analyses have also highlighted areas where the science and knowledge base is limited and where further industry input and additional data analyses are required to provide a rapid response to managers and stakeholders when closed areas are proposed. The studies have been collated as a series of papers, each presented as an independent section. Key points by relevant subject area are summarized below. General points 1) Removal from a fishery of the effort directed into a closed area results in the most significant impact from a closure. If effort is allowed to relocate into areas remaining open, the impact of the closed area is reduced substantially and, in some of the cases examined, mortality on the stock could be increased. Similarly any derogation to fish in a closed area will reduce the area’s impact. Consequently, closed area management cannot be used in isolation from quota and effort regulation and may require lower levels of both. 2) Closed areas are designed to make fishers less efficient at catching protected species. Fishers prevented from accessing local stocks will move into areas that they may not have fished before, resulting in conflict, inefficiency and reduced income. The incentive to provide biased landings and effort data will be greater. Quality of catch and effort data is likely to become even more uncertain, until the stock recovers and pressures are relieved. 3) The approach used by fishers to relocate effort displaced from a closed area is a critical determinant to the effectiveness of a closure. Therefore, case-specific dialogue with fishers during the design process, with regard to potential changes in effort distribution resulting from a closure, is considered to be an important factor in reducing the uncertainty associated with expected returns. 4) Seasonal migration and movement can have a significant impact on the effectiveness of a closed area. Closed areas must be designed to be robust to temporal variability in stock distribution; boundaries may have to be moved during the year or, alternatively, permanent closures may need to be expanded in order to maintain their effectiveness. The North Sea cod fishery 5) At a time of increasing uncertainty in resource status resulting from bias in catch data, closed areas can remove some of the cod stock from exploitation, protecting at least a portion of the resource. For instance, temporary closures to protect juveniles, if implemented quickly, are an effective way of reducing mortality rates. 6) In all cases, removal from the fishery of the effort directed into the closed areas had by far the most significant effect on reducing mortality of North Sea cod. If effort is allowed to relocate into areas remaining open, the reduction in mortality rates reduces substantially and may increase. 2 7) Closed areas that deliver “guaranteed” protection and reductions in cod mortality without reducing current levels of effort would require the closure of substantial parts of the North Sea. The impact of displacing significant proportions of the effort into areas remaining open would be considerable, and it could result in many traditional fishing grounds being closed as well as numerous conflicts of interest. Catches recorded from the North Sea cod fishery have spatial structure within them, indicating possible sub-stock structure. This study has not evaluated the impact that this situation might have for each sub-unit. Closure of an area containing one sub-unit may completely protect it from exploitation while forcing effort onto a second sub-unit, making it more vulnerable to exploitation. 8) The effectiveness of a closed area is conditional on its design with respect to the decisions that fishers must make when they redistribute effort. If fishers target cod with effort displaced from closed areas, the current designs of closed areas suggested by the EU Commission could increase cod fishing mortality rates substantially. Closed area designs based on potential catch rate and total catch are more robust to the way in which effort is relocated. 9) If redesigned, then closed areas of the magnitude suggested by the EU Commission can reduce fishing mortality on cod. However, the estimated reductions in mortality rate are relatively small and, at best, will only stabilize the decline in stock size; they will not result in recovery of spawning stock biomass to safe biological levels. Alternative management strategies 10)The international North Sea fishery selection-at-age estimated by the 2004 ICES Working Group approximates to that of a 90 mm mesh, well below the 120 mm legal minimum mesh for boats targeting cod. Although boats directing fishing effort at gadoids in the North Sea are required to use 120 mm mesh, those deploying a wide range of gear types catch and discard or land cod; the combined effect is a much lower effective mesh selection. 11)The use of 120 mm mesh throughout all of the fisheries catching cod would have the same impact as the reduction of discards to zero, and for an unchanged level of effort results in growth of the stock to BNm. Use of 140 mm mesh increases biomass to between B|im and Bpa, and use of 160 mm allows the stock to recover to above Bpa. The analysis assumes that effort does not increase in order to compensate for the loss of smaller species and the initial losses of small cod from the catch. Larger mesh sizes would result in significant losses of the whiting and haddock from the catch. 3 Mixed fishery aspects 12)Relocating fishing effort away from concentrations of cod will impact on the catch of other species. The small example area on the northeast coast of England for which appropriate data were available gave increased catches of Nephrops throughout the year and whiting and haddock in the first and fourth quarters. 13)Seasonal migration and movement of cod have a significant impact on the catch. Increase in catch rates of associated species will have a strong impact on discard rates if additional quota is not available for displaced boats. Impact on the benthos 14)Closure of fishing grounds will move fishers away from traditional fishing areas, resulting in increased effort and seabed disturbance in areas that were previously relatively lightly fished. 15)There will therefore be a net reduction in diversity and biomass across the North Sea before any increases within the closed areas have had time to accrue. In the simulations, total benthic community biomass start to recover only after more than 10 years. 16)Removing fishing effort displaced by the closed areas always has a positive effect on benthic community biomass and production. 4 Document references Cefas reference: C2465 Cefas Defra reference: SFCD15 REPORT ON INVESTIGATIONS INTO CLOSED AREA MANAGEMENT OF NORTH SEA COD January-May 2005 This report is not to be quoted without prior consultation with Cefas Cefas is an Executive Agency of Defra TABLE OF CONTENTS Section Page Raison d'être 4 1. Introduction 5 1.1 Spatial management of fish stocks 5 1.2 Closed area management of North Sea fish stocks 7 1.2.1 The 1987 North Sea cod box 7 1.2.2 The North Sea cod task force 7 1.2.3 The 2001 cod closed area 8 1.2.4 The 2003 STECF Cod Assessment and Technical Measures Report 9 1.3 Closed area scenarios 10 2. Spatial distribution of North Sea fishing effort 12 2.1 English fleet effort 12 2.1.1 English otter trawl 12 2.1.2 English beam trawl 13 2.2 English fleet effort redistribution in response to closure 14 2.2.1 Background 14 2.2.2 Method: model structure and assumptions 14 2.2.3 Scenarios 15 2.2.4 Results 16 2.2.5 Discussion 17 2.3 International effort 25 2.4 International effort redistribution in response to closure 26 3.
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