1. DRV/RH/Ecohal The influence of climate change on commercial flatfish populations in the Bay of Biscay O. Le Pape, D. Guérault and Y. Désaunay Bergen ICES symposium, May 14 th 2004 The Influence of climate Change on North Atlantic Fish Stocks

2. DRV/RH/Ecohal Study area: Northern bay of Biscay (west coast of France) Continental shelf Important flatfish stocks/fisheries common sole and other species (mainly plaice, dab, wedge sole) Flatfish stocks on the shelf Coastal and estuarine nursery grounds

3. DRV/RH/Ecohal Climate changes Temperate area Increase of winter temperature Steadyness of summer temperature Planque et al., 2003 Expected increase of winter river flow Burger, 2002

4. DRV/RH/Ecohal Local study on a nursery  Validation at stocks/fishery scale  Vilaine Bay high density/viewable variability Synthesis of the consequences

5. DRV/RH/Ecohal Data Annual trawl surveys At the Vilaine Bay scale (for the 2 last decades) At the Bay of Biscay scale (shorter recent period, 15 y)

6. DRV/RH/Ecohal 2 questions Sea warming / species composition River flow / common sole recruitment

7. DRV/RH/Ecohal Flatfish species composition (  T°) 4 species  biogeographic distribution dab and plaice (cold temperate, southern limit) common sole (cold temperate, far from limit) wedge sole (warm temperate, northern limit) Temporal trends in annual abundance (Kendall tests) Juvenile in the Vilaine Bay Adults in the Bay of Biscay (stocks/fisheries)

8. DRV/RH/Ecohal Vilaine Bay (Juveniles) High variability  High variability  Low variability no trend High variability 

9. DRV/RH/Ecohal Bay of Biscay (mainly adults)  

10. DRV/RH/Ecohal Strong concordant signal (Nursery/Stock) Close from limits = higher variability disappearance of the 2 northern specie increase of the southern species steadyness of the common sole A northward shift in stock distribution

11. DRV/RH/Ecohal Why a northward shift ? General conclusion on temperate areas (Brander et al., 2003) Recruitment  stocks Local flatfish specificity/ seasonal  in warming Southern summer spawner / northern winter spawner Temperature = upper limit for spawning, eggs, and larvae low for benthic juvenile growth (shown in situ)  Winter warming = - Disturbance in spawning for northern species - Enhanced growth and survival of southern juveniles  Steadyness of summer temperature - Unchanged spawning of southern species - Unchanged growth of northern juveniles

12. DRV/RH/Ecohal River flow / common sole recruitment Study on Vilaine Bay (juvenile) (Vilaine river flow) Validation on the Bay of Biscay (2-group fish) (5 main river flows)

13. DRV/RH/Ecohal flow / sole settlement Youngest fish = Highest sensibility Important river flow  January - May (5 months period) Rising period = October - May Sole settlement = April - June

14. DRV/RH/Ecohal Vilaine flow / Juvenile abundance r = 0.77  < 10 -3 Vilaine fluvial discharge = positive influence on common sole recruitment (Nursery ground extent increases with river flow) River flow year y / 1 group abundance year y+1

15. DRV/RH/Ecohal Bay of Biscay : Flow / abundance r = 0.58 (Lower)  < 0.05 fluvial discharge = positive influence on common sole recruitment River flow year y / 2 group abundance year y+2

16. DRV/RH/Ecohal River flow  Recruitment Nursery/Stock Estuarine influence Larval transport Productive areas and Feeding habitat settling of benthic preys (Salen-Picard et al., 2002)  Fluvial regime  Recruitment (Sole and probably other flatfish) Favourable expected effect of higher winter flow

17. DRV/RH/Ecohal Climate changes / Flatfish fisheries Juvenile on nursery + Fishery/stock responses Winter warming Northward shift and replacement (Pauly, 1994+ DEB model) large northern species - high interest / small southern flatfish - less interest (Verified here !) Expected higher winter flow Enhanced recruitment for common sole and other remaining estuarine dependent winter spawners A balance between two opposite consequenses  Species composition / expected  sole recruitment