LU 66. zinātniskās konferences sekcija "Klimata mainība un ūdeņi Rīga, 2008.gada 22. februāris The Baltic cod reproduction volume as a proxy for cod year-class strength Maris Plikšs & Bärbel Müller-Karulis Latvijas Zivju resursu aģentūra
Outline The paper examines whether the dynamics in reproduction volume can explain the fluctuations in recruitment of cod can the reproduction volume be used to predict the year-class strength of the Eastern Baltic cod
Kam Baltijas Jūras vajag sālsūdens? Conley et al. 2002
Thank you! Photo: A Craasmann (FishBase)
Ecosystem Baltic Sea Thermocline River run-off Inflow >S >O 2 Halocline Spawn migrations Feeding area Nursery area Spawning habitat Reproduction volume S>11psu O 2 >2ml/l Uplift of anoxic waters during inflow Anoxic deep layer (H 2 S during stagnation) Modified after Köster et al. 2002
Ecosystem Baltic Sea 2nd critical stage: first larvae feeding Thermocline River run-off Inflow >S >O 2 Halocline Spawn migrations Feeding area Nursery area Spawning habitat Reproduction volume S>11psu O 2 >2ml/l 1st critical stage: Egg survival depending from abiotic environment (T,S,O 2 ) Uplift of anoxic waters during inflow Anoxic deep layer (H 2 S during stagnation) Modified after Köster et al. 2002
1000 t Million Eastern Baltic cod stock Eastern Baltic cod stock dynamics Recruitment 900 800 700 600 Age 2 Long term average 500 400 300 200 100 Spawning stock biomass (SSB) 0 1966 1971 1976 1981 1986 1991 1996 2001 800 700 600 500 400 300 B pa 200 100 B lim 0 1966 1971 1976 1981 1986 1991 1996 2001 ICES CM, 2007
Baltic cod reproduction volume Concept Station BY15A August 1976 Temperature, deg C 2 4 6 8 10 12 14 16 18 Salinity: > 11psu (Nissling, 1994) Oxygen: > 2 ml/l (Wieland et al., 1994) Temperature: > 2 deg C (Wieland et al., 1994) 0 Salinity, psu 7 8 9 10 11 12 13 Oxygen, ml/l 0 2 4 6 8 10 T 50 S O 2 Depth, m 100 RV 150 200 Salinity Oxygen Temperature
Baltic Sea Cod spawning areas 60 59 58 57 56 55 Bornholm Deep Gdansk Deep 54 14 16 18 20 22 24
1952 1955 1958 1961 1964 1967 1970 1973 1976 1979 1982 1985 1988 1991 1994 1997 2000 2003 Stdev 1952 1956 1960 1964 1968 1972 1976 1980 1984 1988 1992 1996 2000 2004 km**3 Baltic cod reproduction volume Dynamics 1200 1000 Abundant year classes 800 Regime shift? 600 400 Gotland Gdansk Bornholm 4.5 200 3.5 0 2.5 1.5 0.5-0.5-1.5 Anomalies
Baltic Sea Inflows in the Baltic (Matthäus, 2003)
Baltic Sea Eastern Gotland Basin Bornholm Deep Gdansk Deep
Rs Recruitment dependence from RV Rs versus RV 3 R s recruits per SSB i.e. stock recruitment success 2.5 yc 1971 2!! Poor recruitment and SSB estimates during late 1960 ies and early 1970 ies 1.5 1 0.5 y = 0.0023x + 0.6349 R 2 = 0.3585 p<0.0001 0 0 100 200 300 400 500 600 700 RV, km**3
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Residuals Rs versus RV Recruitment dependence from RV Residuals: Prevalence of positive residuals during regular inflow events till 1980, negative afterwards Residuals by years 1.5 1 0.5 0-0.5-1 Year Overestimation of YC in present environmental regime Underestimation of YC in case of inflow events
Residuals Rs versus RV Recruitment dependence from RV Residuals: Trend from negative residuals to positive with increasing RV (R 2 = 0.39, P> 0.001) y = 0.0022x - 0.4806 R 2 = 0.3904 Residuals versus RV 1.5 1 0.5 0 0 100 200 300 400 500 600 700-0.5-1 RV, km**3 High variation in case of small RV (spawning in one Basin) Underestimation of YC in case of high RV
1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 Milj.ind. Recruitment dependence from RV Prediction of R 1000 800 600 400 Inflow 1993 200 0 Year-class R age2, observed R age 2 predicted (thousands) Geomean (10yrs) Other interactions neglected, as: 1) Cannibalism (Uzars & Plikshs, 2000; Köster et al 2000) 2) Pelagic fish feeding on cod eggs (Köster & Möllmann, 2000) 3) Larval survival (Hinrichsen et all, 2002) 4) SSB structure and spawners quality (Marshall, 1998; Kraus et al, 2002)
Summary The reproduction volume is the primary parameter for success of reproduction and recruitment of the Baltic cod Abundant year classes of cod in the Baltic Sea can only be observed if the conditions for embryonic development are suitable in all principal spawning areas of cod in the Baltic
Summary Recent failure of recruitment is determined by regime shift in the Baltic, i.e. decrease of salinity in the Deep basins and water exchange with North sea During recent environmental conditions (RV only in Bornholm Basin) obviously high importance have other cod recruitment limiting factors e.g. first larvae feeding RV can be used in prediction of year-class strength of Baltic cod and performs comparable with the presently used 10 recent year geometric mean
Thank you! Photo: A Craasmann (FishBase)