Spatial patterns in the distribution and early life characteristics of North Sea cod under the influence of climate change Hannes Höffle, Ph.D. student DTU Aqua Section Oceanography Supervisors: Peter Munk, DTU Aqua Brian MacKenzie, DTU Aqua Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name2DTU Aqua, Technical University of Denmark Table of contents 1.Background: The cod stock in the North Sea and the early life 2.Results of IBTS cruises 2004 and 2009 (preliminary) 3.Comparison of the two years and outlook to future work Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name3DTU Aqua, Technical University of Denmark The cod stock in the North Sea – How much is left? The Spawning Stock Bioass (SSB) is estimated to be around 50,000 t. Climate impacts on the Baltic Sea, Bornholm 09 ICES 2006

17/04/2008Presentation name4DTU Aqua, Technical University of Denmark The early life – a critical stage Predation Physiological stress Disease Problems in Development Pollution Starvation Recruitment Climate impacts on the Baltic Sea, Bornholm 09 Fuiman & Werner 2002

17/04/2008Presentation name5DTU Aqua, Technical University of Denmark What does a cod larvae need and how might climate influence that? Food: i.e. Calanus finmarchicus Suitable Salinity Suitable OxygenSuitable Temperature Faster metabolism More active (and more?) predators Balance of Turbulence and Stratification Supply from Atlantic Transport weakened since mid 80’s More and stronger extreme weather events Higher inflow and precipitation may change position of front Less soluble Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name6DTU Aqua, Technical University of Denmark How to assess the cod stock in the future? - The SUNFISH project SUNFISH = Sustainable Fisheries, Climate Change and the North Sea ecosystem Problem: Extrapolating from historical observations may be unreliable in the future Objectives: 1.Understand and evaluate climate change effects 2.Quantify effects on fishes Climate impacts on the Baltic Sea, Bornholm 09 Approach: Cod (Gadus morhua) Sandeel (Ammodytes sp.) Drift & Dispersal during early life Predictive models Including environmental cues

17/04/2008Presentation name7DTU Aqua, Technical University of Denmark Cod eggs, larvae and pelagic juveniles – my part of the story Climate impacts on the Baltic Sea, Bornholm Distribution of eggs & early larvae Fixed behaviour or hydrography? 2. Determinantes for drift and dispersal? 3. Prey preference & Settlement Do they run out of pelagic food?

17/04/2008Presentation name8DTU Aqua, Technical University of Denmark Investigation of early life stages – IBTS 1Q 2004 Hypothesis: Spawning areas are linked to recurrent hydrographic features like Salinity fronts. Indicators for spawning areas: -) Mature females in trawls -) eggs & larvae in plankton samples Findings: High Gadoid egg abundances:-) at Dogger bank -) at Fisher Banks -) off Norwegian coastal current -) off northern Scotland High plaice egg abundances: -) at Fisher Banks -) off Norwegian coastal current Early stage larvae were abundant where eggs occurred in high concentrations. Peak egg and larvae abundances corresponded to (frontal) hydrography. Salinity fronts may change due to climate change, because of shifts in FW-inflow. Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name9DTU Aqua, Technical University of Denmark Investigation of early life stages – IBTS 1Q 2004 Climate impacts on the Baltic Sea, Bornholm 09 Depth Salinity

17/04/2008Presentation name10DTU Aqua, Technical University of Denmark Sampling of cod ovaries during the day shift In total 68 plankton samples taken Sampling between 18:00 hours and 07:00 hours Sampling gear: Bongo Net with CTD and Depth Sounder Preservation of samples in Ethanol (500 µm) and Formaldehyde (330 µm) Sorting of single egg samples onboard (sample in Seawater on ice) IBTS – cruise 1Q st January – 17 th February 2009 Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name11DTU Aqua, Technical University of Denmark Ditstribution of Eggs in the North Sea Depth Climate impacts on the Baltic Sea, Bornholm 09 Total eggs counted: 9462 Calculated number of eggs in Samples: 51,445

17/04/2008Presentation name12DTU Aqua, Technical University of Denmark Distribution of Eggs in the North Sea Climate impacts on the Baltic Sea, Bornholm 09 Depth

17/04/2008Presentation name13DTU Aqua, Technical University of Denmark Size range of Eggs sampled in 2009 Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name14DTU Aqua, Technical University of Denmark How does 2009 compare to 2004? Gadoids Gadoids 2004 Gadoids 2009 Climate impacts on the Baltic Sea, Bornholm 09 Salinity

17/04/2008Presentation name15DTU Aqua, Technical University of Denmark What determines the major distributional patterns of cod eggs and early larvae? 2009 data is preliminary, changes may occur Difference in absolute number may be due to different timing of surveys. Reduced number of Gadoids south of Dogger Bank. Shift of Salinity front? Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name16DTU Aqua, Technical University of Denmark Outlook to future work Next cruise: IBTS 3Q 2009, 11th to 28th of August 2009 Target: Pelagic juvenile Cod (and other Gadoids) New questions: –Does cod prefer to spawn along certain salinity isolines? –Will there be new predators on larval and juvenile cod? –How will more events of extreme weather influence the survival? Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name17DTU Aqua, Technical University of Denmark Acknowledgements Peter Munk for a crash course in Surfer 7. Erik Selander for microscope photos. Zeren Gürkan and Niels Jørgen Pihl for help during the field sampling. Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name18DTU Aqua, Technical University of Denmark Thank you for your attention!