13/02/2012 Recruitment variability in North Sea herring Pelagic RAC - PDF document

13/02/2012 Recruitment variability in North Sea herring Pelagic RAC 8 February 2012 150 recruitment North Sea herring Recruitment failures in North Sea herring 100 0-group x 10 9 Ad Corten 50 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 3 possible causes of sustained low recruitment Comparison of two periods with low recruitment 150 2,5 1) insufficient egg production recruitment Period 2 recruitent as 0-group x 10 9 2 SSB 2) long-lived predators spawning stock in million tons 100 1,5 3) oceanic processes Period 1 1 50 0,5 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Long-lived pelagic predators in Period 2 Comparison of two periods with low recruitment 150 2,5 • mackerel recruitment Period 2 2 recruitent as 0-group x 10 9 SSB • horse mackerel spawning stock in million tons 100 1,5 • herring ? Period 1 1 50 0,5 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Reduced Atlantic inflow 1

13/02/2012 Experiments on cannibalisme at RIVO in 1983 (1) Experiments on cannibalisme at RIVO in 1983 (2) Larvae 15 minutes Larvae 30 minutes after ingestion after ingestion Experiments on cannibalisme at RIVO in 1983 (3) Cannibalism in Sardinella maderensis (1) Larvae 60 minutes after ingestion 0 0 4W 0 0 8E 0 4E Cannibalism in Sardinella maderensis (2) Drift of larvae and migration of adults 0 62 after spawning 200 m 0 60 Shetland Orkney 0 58 Aberdeen Bank 0 56 Central North Sea 0 54 0 52 spawning area nursery area drift larvae 0 50 English Channel adults 2

13/02/2012 Cannibalism explains low recruitment in recent period, and Spawning stock and recruitment 1970 - 2009 high recruitment in 1980 - 1985 150 2,5 120 recruitment Low recruitment 1970 - 2009 SSB 2 100 recruitent as 0-group x 10 9 High recruitment spawning stock in million tons 100 80 1,5 recruitment 60 1 50 40 0,5 20 0 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 0 0,5 1 1,5 2 2,5 Spawning stock in million tons Precautionary approach by ICES Hockey stick relationship used by ICES 120 1960 1985 100 8 e+07 1986 1984 1998 80 B lim B pa B trig Recruitment 1981 1991 recruitment 1963 1982 1995 1983 1992 60 4 e+07 1999 1962 1961 1994 1987 1969 1966 1980 1967 1988 1993 1989 1964 1990 1970 1996 40 1965 1997 1973 1968 1971 1979 20 1978 1972 0 e+00 1977 1976 1975 1974 0 0 500000 1000000 1500000 2000000 0 0,5 1 1,5 2 2,5 Spawning stock in million tons SSB Cannibalism at high stock sizes is also a management risk SSB dropping below B lim is not the end of the world 150 2,5 recruitment and spawning stock recruitment 120 SSB 2 recruitent as 0-group x 10 9 100 spawning stock in million tons Low egg 100 Cannibalism production 80 1,5 recruitment 60 1 B lim 50 40 0,5 20 0 0 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 0 0,5 1 1,5 2 2,5 Spawning stock in million tons 3

13/02/2012 Conclusions • Cannibalism offers a simple explanation for the low recruitment in recent years, and also for the exceptionally good recruitment in the Thank you for your period 1980-1985 when adult stock size was low attention • If adult stock size is maintained at levels > 1.5 million tons, recruitment will probably stay below average and the North Sea herring stock will not produce its maximum yield • ICES should consider the effects of cannibalism on recruitment, and its consequences for management Period 1: scarcity of Atlantic plankton suggests reduced Period 2: no reduced oceanic inflow into North Sea oceanic inflow into northwestern North Sea 6 1.4 6 1.4 Metridia lucens Metridia lucens Period 2 Candacia armata Candacia armata 1.2 1.2 5 5 Metridia lucens Metridia lucens Candacia armata Candacia armata 1 1 4 4 0.8 0.8 Period 1 3 3 0.6 0.6 2 2 0.4 0.4 1 1 0.2 0.2 0 0 0 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 0 0 4W 0 0 8E 0 4E Period 1: reduced Spawning stock and recruitment 1960 - 2009 Atlantic inflow into the 0 62 North Sea probably inflow slowed down transport 120 200 m 1960 - 2009 of larvae to nursery 0 60 areas 100 Shetland Orkney 0 58 80 Aberdeen recruitment Bank 60 0 56 Central North Sea 40 0 54 20 0 52 spawning area nursery area 0 0 0,5 1 1,5 2 2,5 drift larvae 0 50 English Channel Spawning stock in million tons 4

13/02/2012 Changes in stock structure after 1975 Changes in plankton composition in central North Sea Northeast Bank West Dogger Flamborough Whitby Dowsing Sandettie Dieppe 1976-92 1955-75 Seine Bay Source: SAHFOS Distribution of herring larvae in February 2011 Annual yield North Sea herring at two different levels of SSB 1400000 1200000 Annual catch in tons 1000000 800000 Catch at SSB 600000 0.5 – 1.0 million t 400000 200000 Catch at SSB > 1.5 million t 0 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 5