Effects of climate variation on young fish

Transcription

1 Nordic Climate-Fish 2nd Conference: Latitudinal changes in marine resources, exploitation and society within the Nordic and adjacent Seas August 2012 in Risør, Norway Effects of climate variation on young fish Geir Ottersen general ideas about climate effects on marine ecosystems variations in temperature-zooplankton-north Sea cod spatial population structure and detecting climate effects

2 How Does Climate Affect Fish? Predators Recruitment Distribution and migration Physiological Effects Metabolic processes Growth Prey Modified from slide by Ken Drinkwater, IMR Disease

3 Ecological response to climate signal Linear ecological response to climate signal Single climate event causes shift in ecological state Linear climate signal causes shift in ecological state when climate threshold passed. Ecological Response Climate Time Ottersen, Stenseth, Hurrell 2004 Climate fluctuations. Oxford Univ. Press

4 Linear ecological response to climate signal Ln(Recruitment) Cod at West Greenland Recruitment Temperature SST Year Stein and Borovkov

5 Single climate event causes shift in ecological state El Niño: Human and Climate induced crash in Peruvian anchovy stock

6 Variations in temperature-zooplankton-north Sea cod Increasing sea temperatures M. Llope, Instituto Espanol de Oceanografia Cadiz Changes in plankton composition May this gradual change cause a shift in ecological state when threshold passed? M. Edwards, SAHFOS (2008)

7 Shift in transfer of energy from pelagic fish to benthos Higher temperatures leading to an increase in the abundance of phytoplankton earlier in the year has changed the food web structure through competitive exclusion of holozooplankton by meroplankton (i.e., less organisms that are planktonic for their entire life cycle, more that are planktonic only during larval stages, thereafter benthic). The result is significantly diminished transfer of energy towards top pelagic predators (e.g. fish) and increased transfer to the benthos. ICES STATUS REPORT ON CLIMATE CHANGE IN THE NORTH ATLANTIC (eds. P.C. Reid and L. Valdes) September 2011

8 North Sea cod 2000 Recruitment (age 1) Recruitment in millions ICES Mean temperature in region Age-2 ambient temperature Age-4 ambient temperature Increasing ambient temperatures for cod IBTS Q1 G. Dingsør, G. Ottersen et al. In prep

9 Switch from C. finmarchicus (prefered food of larval cod) Calanus finmarchicus female towards C. helgolandicus Calanus helgolandicus female in the North Sea Edwards et al Ecological Status Report, SAHFOS, UK

10 Switch from C. finmarchicus towards C. helgolandicus in the Skagerrak Monitoring of plankton at station in the Skagerrak, off Arendal: Sampling of zooplankton: 2 times per month since 1994 WP2 vertical net tows (180µm), 50 0 m Samples recently reanalysed for identification of C. fin and C. hel Aims: - To describe the seasonal and interannual variation in relative proportions of the two species. - Reveal possible causes for the observed variations. T. Falkenhaug, E. Bagøien, C. Broms, IMR work in prep.

11 Seasonal and interannual variations in ratio of C. finmarchicus/ C. helgolandicus CVI females 1= 100% C. finmarchicus (blue) 0=100% C. helgolandicus (red) Month Year The period of C. helgolandicus dominance (ratio>0.5) has appeared earlier in the season in recent years ( ). T. Falkenhaug, E. Bagøien, C. Broms, IMR work in prep.

12 North Sea cod Enhancing stock-recruitment models by including climate and zooplankton in a combined Beverton-Holt and Ricker model (5 temperature regimes[panels], 3 levels of food [curve patterns]) Recruitment Very cold Cold Average Warm Very warm Spawning stock biomass

13 Conclusions calanus and cod C. finmarchicus occur in high abundance in spring, while C. helgolandicus peaks later in the season at lower abundances. The seasonal increase in temperature triggers a shift from a system dominated by C. finmarchicus to a system dominated by C. helgolandcus. This shift occurs in June, at ~13 ºC. Higher temperatures, earlier in the season will trigger earlier shifts from C.fin to C.hel. The stock-recruitment relationship of North Sea cod is not stationary, its shape depends on food (zooplankton) availability and sea temperature The change in calanus is bad news for early life stages of cod, which have Cal.fin. as preferred food, and is thus negative for recruitment.

14 Including spatial population structure helps detect effects of climate on population dynamics Stocks, i.e. management units, need not be real biological units (populations) but may consist of distinct spawning units with low levels of inter-mixing Spatial population structure is increasingly recognized in marine fishes: e.g., cod, yellowtail flounder, herring Climate effects are expected to be more difficult to detect if spatial structure is unaccounted for

15 Example from current research on Skagerrak coastal cod (using beach seine data on 0-group) Estimated mean and 95% Credible Intervals for β.sst: β.sst Larval SST With population structure Lauren Rogers, CEES UiO

16 Temperature effect appears weaker and becomes harder to detect if we ignore population structure. Estimated mean and 95% Credible Intervals for β.sst: Ignoring population structure! β.sst Larval SST With population structure Lauren Rogers, CEES UiO

17 Image: Glynn Gorick for ICES WG Cod and Climate Change Thanks, that s all