hannes höffle, ph.d. student dtu aqua section oceanography supervisors: peter munk, dtu aqua

Spatial patterns in the distribution and early life characteristics of North Sea cod under the

influence of climate change

Hannes Höffle, Ph.D. studentDTU AquaSection Oceanography

Supervisors: Peter Munk, DTU AquaBrian MacKenzie, DTU Aqua

Climate impacts on the Baltic Sea, Bornholm 09

17/04/2008Presentation name2 DTU 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



The cod stock in the North Sea – How much is left?

• The Spawning Stock Bioass (SSB) is estimated to be around 50,000 t.


ICES 2006


The early life – a critical stage

Predation

Physiological stress

Disease

Problems in Development

Pollution

Starvation

RecruitmentClimate impacts on the Baltic Sea, Bornholm 09

Fuiman & Werner 2002


What does a cod larvae need and how might climate influence that?

Food: i.e. Calanus finmarchicus

Suitable SalinitySuitable 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


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


Approach: Cod (Gadus morhua)

Sandeel (Ammodytes sp.)

Drift & Dispersal

during early life

Predictive models

Including environmental cues


Cod eggs, larvae and pelagic juveniles – my part of the story


1. 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?


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.



Investigation of early life stages – IBTS 1Q 2004


DepthSalinity


•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 200931st January – 17th February 2009

581012

20

22

2426283032

41

4951535559

61 6371

73

7577

79

81

89919397

99 101

110112 114 116

118126

128

130

132

134136

138

149

152156

165173

176179

190193

196200

215217219221

223225

-3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12

Longitude

D anish Bongo sam pling IBTS 2009

50

51

52

53

54

55

56

57

58

59

60

61

La

titud

e

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

E6 E7 E8 E9 F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 G 0 G 1 G 2



Ditstribution of Eggs in the North Sea

DepthClimate impacts on the Baltic Sea, Bornholm 09

Total eggs counted: 9462

Calculated number of eggs in Samples: 51,445


Distribution of Eggs in the North Sea


Depth


Size range of Eggs sampled in 2009



How does 2009 compare to 2004?Gadoids

Gadoids 2004Gadoids 2009


Salinity


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?



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?



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.



Thank you for your attention!

hannes höffle, ph.d. student dtu aqua section oceanography supervisors: peter munk, dtu aqua

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