Evaluation of the Minimum Landing Size for Mackerel in the North Sea and Western Waters Martin Pastoors, 30 March 2015 Introduct
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Evaluation of the minimum landing size for mackerel in the North Sea and Western Waters Martin Pastoors, 30 March 2015 Introduction The new landing obligation in EU fisheries creates an incentive to critically review the role of Minimum Landing Size (MLS), now called Minimum Conservation Reference Size (MCRS). Because all quota regulated fish under MCRS need to be landed but may not be used for direct human consumption, it is important to verify that the scientific background of the MLS actually reflects a sound reasoning that can underpin the MCRS concept. This paper specifically deals with the MLS for mackerel. For this species the MLS for the North Sea has been set at 30 cm and for the other areas at 20 cm. At the same time, a substantial portion of the catch of the Western Stock component is taken in the northern North Sea under a special condition (between September and January). The recent interpretation from the EC and Member States is that the 30 cm minimum size also applies to mackerel caught under the flex arrangement. So what is the rationale behind these MLS values and how do they apply to the different stock components identified by ICES? To address that question, a historical analysis of MLS will be carried out, going back over policy documents (e.g. technical measures), ICES documents (working group reports, advisory reports) and some scientific papers. In addition, the composition of mackerel catches (age, size, maturity stage) was analyzed to address the overall maturity stage in relation to potential arguments for setting MCRS. Material and methods A backwards snowballing method has been used to trace the history of MLS for mackerel. Starting with the most recent scientific advice on mackerel (ICES 2014a), the references to expert group reports and regulations were followed up. All references to MLS were quoted and references to earlier reports were then investigated. This lead to a year range of 1968-1998 as the most informative range on the background of the mackerel MLS. The most recent stock assessment of mackerel (ICES 2014b) was used as a basis to assess the maturity stage of current catches of mackerel and how that relates to potential indicators for MCRS. Results History of scientific advice and decisionmaking An overview of historical documents advising on or setting values for MLS of mackerel are shown in Appendix 1 and summarized below. Year Type Reference Contents 1968 Paper (Revheim and Proposed to raise the minimum legal size of mackerel for industrial Hamre 1968) purposes to 30 cm 1974 Working (ICES 1974) A 33 cm minimum landing size would give practically the same yield per group recruit and would give a better condition of the stock than one of 30 cm. For practical reasons, however, 30 cm is preferable. 1981 Advisory (ICES 1982) ACFM recommends a minimum landing size of 30 cm for mackerel in all Committee areas 1986 Advisory (ICES 1987) More general protection could be achieved by adoption of a minimum Committee landing size and ACFM recommends the introduction of a 30-cm limit for mackerel in all areas. Year Type Reference Contents 1986 Regulation (Council of the Minimum Landing Size for Mackerel (Scomber scombrus): Region 2 European Union North Sea only 30 cm, Region 3 to be determined. 1986) 1987 Advisory (ICES 1988) North Sea mackerel: “The 30-cm minimum landing size at present in Committee force in the North Sea should be maintained.” Western Mackerel: “ACFM reiterates its recommendation that a 30-cm minimum landing size should be implemented in all areas.” 1989 Working (ICES 1989) “The 30-cm minimum size limit was originally introduced in the North group Sea by Norway in 1971 and was intended to protect the very strong 1969 year class from exploitation in the industrial fishery. It does not seem necessary to extend this measure to the Western area. The introduction of a 30-cm minimum size in the area in order to make it consistent with similar measures in the North Sea may result in an increase in the quantities of juvenile mackerel which will be slipped or discarded.” 1989 Advisory (ICES 1990a) “In the Western area, juvenile and adult mackerel were found to occur Committee within the same fishing locations, and an introduction of a minimum landing size could lead to a higher discard rate. ACFM, therefore, concluded that there would be no benefit from adopting a 30-cm minimum landing size in the Western area.” 1990 Working (ICES 1990b) “Again, as expressed in 1989, the introduction of a 30 cm minimum size Group for the Western area does not seem necessary on biological grounds and would lead to a higher discard rate when a strong year class enters the fishery.” 1991 Proposal for (Commission of the [unfortunately this document is not available of Eurlex] regulation European Communities 1991) 1992 Regulation (Council of the Minimum Landing Size for Mackerel (Scomber scombrus): Region 2 European Union North Sea only 30 cm, Region 1, 2, 3 and 5 (except North Sea): 20 cm. No 1992) underpinning of 20 cm provided. 1993 Working (ICES 1993a) “there appears to be no reason why fishing on the western stock should group not be permitted in Divisions Iva and Iia during the third and fourth quarters.” 1998 Regulation (Council of the Minimum Landing Size for Mackerel (Scomber scombrus): whole area European Union except North Sea: 20 cm. North Sea: 30 cm 1998) The historical overview shows a number of important points: The MLS of 30 cm in the North Sea was originally introduced by Norway in 1971 and was intended to protect the very strong 1969 year class from exploitation in the industrial fishery. The 30 cm became the norm for the North Sea MLS on the basis of productivity assumptions. In the early 1980s, ICES recommended to introduce the 30 cm MLS for mackerel in other areas in order to protect juvenile mackerel from being caught. A full review by the Mackerel Working Group in 1989 resulted in a change of perception within ICES. It was no longer recommended to apply a 30 cm MLS for mackerel in other waters than the North Sea because it was expected to result in increased discards. The MLS for mackerel in western waters was set at 20 cm in 1992. Unfortunately, the underpinning of that regulation (i.e. the European Commission proposal) is no longer available, so that the arguments cannot be reviewed or tested. The MLS of mackerel in North Sea (30 cm) and other waters (20 cm) has remained in place since 1992 and have not been critically reviewed since. Mackerel catch composition Catch numbers at age, weight at age (in the catch) and proportion mature of NEA mackerel were taken from WGWIDE 2014 (ICES 2014b). These variables were multiplied to derive the proportion of mature catch in weight and in numbers. This indicates that for the recent period (2000-2013), the landed catches consisted for 95% (weight) or 89% (numbers) of mature mackerel. Catch compositions of Dutch freezer-trawlers fishing mackerel under the flex conditions, generally resulted in catches of mackerel of 25 cm and above. Figure 1 NEA mackerel. Proportion of mature catch in numbers and in weight. Data calculated from WGWIDE 2014. Conclusions Mackerel MLS in North Sea and Western Waters have largely been set on historically developed values without a very strong scientific underpinning or review. Over the past years, the MLS of 20 cm has been used for catches of mackerel in the North Sea under the special condition in the TAC and Quota regulation (even though the MLS was formally at 30 cm for the whole of the North Sea) The current practice of application of 20 cm MLS for western mackerel appears to deliver catch compositions that are largely consisting of mature fish (95% in weight, 89% in numbers). Recommendation Given the need to define MCRS under the landing obligation in order to make optimal use of the natural resources without jeopardizing the reproductive capacity of the stocks, it can be recommended to apply the 20 cm MLS of western mackerel also to the fishery that takes place under the flex arrangements in the North Sea and to include that reference in the special conditions that are allowed from 1st September to 15 February. Appendix 1 Excerpts from ACFM report, WG reports and scientific papers Revheim, A., and Hamre, J. 1968. A brief statement on the present state of the Norwegian mackerel fishery. ICES C.M. 1968 / H:24. “The minimum legal size limit of mackerel for reduction is at present 20 cm. This low size limit has practically no effect on the purse-seine fishery off the coast, but was in fact introduced in order to protect the 0-age group of mackerel which occurs regularly in inshore waters during late Summer and Autumn. The increased exploitation of the mackerel stock in general and the winter landings of immature fish in particular, have given raise to suggestion of a higher minimum size limit than 20 cm, The question has been considered by the Institute of Marine Research which has proposed to raise the minimum legal size of mackerel for industrial purposes to 30 cm with 25 % allowance of under sized fish. (…) This new minimum size level has thus been suggested more on a practical basis than on a scientificly founded assessment of the stock. But such a suggestion must in any case has as aim to increase the sustain yield of the stock at the existing level of exploitation” (Revheim and Hamre 1968) Mackerel Working Group 1974 2. The Effect of Minimum Size Regulation.