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Apr 09, 2023 •354 likes •409 views

120 2.5 ICES Workshop on Limit and Target Reference 100 2 recruitment as O-ringers in bllions Points (WKREF) SSB in million tons 80 1.5 Gdynia, Poland, 29 January 2 February 2007 Bpa 60 1 Blim 40 0.5 20 0 0 1960 1965 1970

  1. 120 2.5 ICES Workshop on Limit and Target Reference 100 2 recruitment as O-ringers in bllions Points (WKREF) SSB in million tons 80 1.5 Gdynia, Poland, 29 January – 2 February 2007 Bpa 60 1 Blim 40 0.5 20 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 B lim : limit stock size Terms of reference for the meeting -minimum spawning stock required for the production of average recruitment review and update the biological basis of limit reference or points for fish stocks in the ICES area, taking into account the possible effects of species interactions and regime shifts. - stock level “below which recruitment is impaired” As a minimum the limit reference points for North Sea herring, Norwegian spring spawning herring, North Sea cod, Baltic cod and Kattegat sole stocks; B pa : precautionary stock size - stock size at which the risk of the stock accidentally being below Blim is minimal Reference points North Sea herring 120 A B 100 Type Value Technical basis 80 B lim 800 000 t below this value poor recruitment has been experienced. recruitment 60 40 B pa 1 300 000 t part of a harvest control rule based on simulations. 20 0 0 0.5 1 1.5 2 2.5 spawning stock in million tons 1

  2. 120 120 100 100 80 80 recruitment recruitment 60 60 40 40 20 20 0 0 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 spawning stock in million tons spawning stock in million tons Example 1 Example 2 The danger of going below Blim is Blim Bpa very high. Consequently, it is wise Although recruitment to set a precautionary Bpa at a Blim Bpa starts declining below sufficiently large distance from Blim, the initial decline Blim. This will minimise the risk of recruitment is not very steep. The stock collapse. recruitment effect on recruitment of reducing the stock a little bit below Blim is small. Consequently, setting an extra safety margin (Bpa) above Blim seems to be unnecessary . spawning stock spawning stock Example 3 Here we have a dome-shaped Blim Bpa relation. According to the ICES definition, Blim is defined as the top of the recruitment curve. If we add a safety margin and put Bpa at some distance to the right side of Blim, we find that recruitment will be reduced in the range of stock size that we consider acceptable (to the right-hand side of Bpa. spawning stock 2

  3. 1952-1974 21.37 21.37 140 16 16 120 14 14 Recruitment as 0-group in billions Recruitment as 0-group in billions 12 12 100 10 10 80 8 8 60 6 6 40 4 4 20 2 2 0 18 18 20 20 0 1 2 3 4 5 6 2 2 4 4 6 6 8 8 10 10 12 12 14 14 16 16 Spawning stock size x 100,000 tons Spawning stock size x 100,000 tons 1960 1 9 6 0 1985 1 9 8 5 8 e+07 2 0 0 0 07 1986 1 9 8 6 8 e+ 1984 1 9 8 4 1998 Recruitment ent 1 9 9 8 1981 1991 1 9 8 1 1963 1982 1 9 9 1 1 9 6 3 Recruitm 1 9 8 2 1995 1983 1992 1 9 8 3 1 9 9 5 4 e+07 1 9 9 2 1999 1962 4 e+07 1961 1 9 6 2 1 9 6 1 1994 1969 1987 1 9 8 7 1966 1 9 6 9 1 9 9 4 1 9 9 9 1 9 6 6 1967 1988 1 9 8 8 1980 1 9 8 0 1 9 6 7 1993 1989 1964 1 9 8 9 1 9 6 4 1990 1 9 9 3 1 9 9 0 1970 1996 1 9 7 0 2 0 0 1 1965 1 9 9 61 9 9 7 1997 1 9 6 5 1973 1968 2 0 0 3 2 0 0 4 1971 1 9 1 7 3 9 7 1 1 9 6 8 2 0 0 2 1979 1 9 7 9 1978 1972 1 9 7 8 1 9 7 2 0 e+00 00 1977 1976 1 9 1 7 9 7 7 6 1975 1974 0 e+ 1 9 7 4 1 9 7 5 0 500000 1000000 1500000 2000000 0 500000 1000000 1500000 2000000 SSB SSB 3

  4. Conclusion on North Sea herring No basis for changing Blim based on current analysis. SGRECVAP results could be basis for revisiting reference point. The distance between Bpa and Blim defines a risk and should be evaluated in the context of harvest control rules in consultation with stakeholders and managers. 4

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