Climate impact on fish productivity: key mechanisms in North Sea plaice

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Herman Brouwer
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1 Climate impact on fish productivity: key mechanisms in North Sea plaice A.D. Rijnsdorp, R. van Hal, M. Hufnagl, R.D.M. Nash, A. Schroeder, L.R. Teal, I. Tulp, R. Witbaard, D. Beare, H.W. van der Veer Wageningen IMARES is een samenwerkingsverband tussen Wageningen UR en TNO

2 Objectives and approach Objectives Study role of climate change and fishing on changes in productivity Approach Bottom up approach focused on key mechanisms Life cycle perspective connectivity Habitat availability North Sea plaice as a research model Focus on pelagic egg/larvae and demersal juveniles

3 The North Sea and plaice living in it DEPTH CURREN T German Bight Wadden Sea Spawning Separate habitat Nursery sites Habitat connectivity areas Harding et al. 1978

4 Changes in the productivity of North Sea plaice Yield Body / growth recruit (kg) Cold years 0.1 Yield Body per growth recruit CV=13% Recruitment CV=50% Recruitment (10^6) Cohort 0

5 Recruitment and connectivity How will climate change affect long-shore residual currents? Bolle et al 2009 MEPS 390:

6 Recruitment Variation in recruitment determined by egg / larval mortality Overall level of recruitment is determined by available nursery grounds North Sea Van der Veer et al 2000 ICES JMS 57:

7 Larval supply to the nursery areas Low temperatures improve egg/larval survival but increase transport duration Recruitment is negatively affected mainly by transport distance Future strength of the current unknown Nursery size determines population size

8 Habitat quality of the nursery areas Temperature tolerance of juvenile plaice Marsdiep August monthly mean temperature inlet of the Wadden Sea 21 temperature * Daily measurements year Van Aken, NIOZ website

9 Habitat quality nursery areas Summer temperature may exceed upper tolerance limit Shifts in distribution to deeper (colder) waters Growth condition may be further limited in summer when temperatures are high and inter / intra-specific competition may be higher due to a decrease in nursery habitat availability

10 Temperature controlled growth of plaice determined by DEB Growth rate in August/September of 1-group plaice (15+ cm) 1963 cold 2003 warm ECOSMO-model data, Schrum et al. Next step is including food, to estimate a more realistic growth

11 Depth distribution of plaice 25-30cm 20-25cm 15-20cm

12 Competition Decrease in available food (Climate/De-eutrophication) Increase in small bodied Lusitanian flatfish species (Climate) (van Hal et al JSR in print). Polychaetes German Bight Plaice box area bivalves Schroeder et al (2010)

13 Conclusions Variations in productivity determined mainly by recruitment and for a smaller part by growth. Recruitment determined in pelagic phase (survival and transport success) Nursery grounds are critical habitat (bottleneck) Global warming will change nursery habitats and thus productivity Observed shift to deeper water is related to increase in temperature in conjunction with decrease in benthic food

14 Implications for fisheries and management The changes in distribution have implications for the management. The effectiveness of MPA s can change (Plaice box) Increase in discard mortality and thus a lower productivity of marketable plaice. Proportion within plaice box <=15cm cm cm

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