The Baltic cod reproduction volume as a proxy for cod year-class strength

Transcription

1 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

2 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

3 Kam Baltijas Jūras vajag sālsūdens? Conley et al. 2002

4 Thank you! Photo: A Craasmann (FishBase)

5 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

6 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

7 1000 t Million Eastern Baltic cod stock Eastern Baltic cod stock dynamics Recruitment Age 2 Long term average Spawning stock biomass (SSB) B pa B lim ICES CM, 2007

8 Baltic cod reproduction volume Concept Station BY15A August 1976 Temperature, deg C Salinity: > 11psu (Nissling, 1994) Oxygen: > 2 ml/l (Wieland et al., 1994) Temperature: > 2 deg C (Wieland et al., 1994) 0 Salinity, psu Oxygen, ml/l T 50 S O 2 Depth, m 100 RV Salinity Oxygen Temperature

9 Baltic Sea Cod spawning areas Bornholm Deep Gdansk Deep

10 Stdev km**3 Baltic cod reproduction volume Dynamics Abundant year classes 800 Regime shift? Gotland Gdansk Bornholm Anomalies

11 Baltic Sea Inflows in the Baltic (Matthäus, 2003)

12 Baltic Sea Eastern Gotland Basin Bornholm Deep Gdansk Deep

13 Rs Recruitment dependence from RV Rs versus RV 3 R s recruits per SSB i.e. stock recruitment success 2.5 yc !! Poor recruitment and SSB estimates during late 1960 ies and early 1970 ies y = x R 2 = p< RV, km**3

14 Residuals Rs versus RV Recruitment dependence from RV Residuals: Prevalence of positive residuals during regular inflow events till 1980, negative afterwards Residuals by years Year Overestimation of YC in present environmental regime Underestimation of YC in case of inflow events

15 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 = x R 2 = Residuals versus RV RV, km**3 High variation in case of small RV (spawning in one Basin) Underestimation of YC in case of high RV

16 Milj.ind. Recruitment dependence from RV Prediction of R Inflow 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)

17 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

18 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

19 Thank you! Photo: A Craasmann (FishBase)