The evaluation of the historical data on fish population versus climate conditions led to a clear identification of temperature as the crucial factor in determining the performance of cod populations in a latitudinal cline, a conclusion corroborated by the application of adequate modelling which demonstrated that sea surface temperature clearly exerts a relevant influence on cod recruitment dynamics in the Kola region (Barents sea) as well as in the North Sea.
Quantification of production (growth, fecundity) in different stocks based on field and experimental data indicate an inverse relationship with temperature. For eelpout as well as for cod growth performance and fecundity decrease significantly at higher latitudes. The results further on suggest that there is a thermal tolerance window of which the North and Barents Seas represent the upper and lower limits, respectively, for both fish species. Nonetheless, the thermal optimum of growth rate of all cod population studied was found at 10 C.
The investigation of blood circulation confirmed the conclusion that thermal tolerance is oxygen limited and that the mismatch between oxygen demand and oxygen supply to tissues during temperature increase is a result of circulatory malfunction. Modelling of physiological data and protein sequences indicated a stronger effect of temperature on the oxygen transport system than on key enzymes of anaerobic metabolism. These combined results of physiological, ecological and modelling data support and widen the basis for a comprehensive hypothesis recently developed to explain the limiting effects of temperature change on marine coastal fishes.
Respiration measurements and mitochondrial investigations corroborated a higher capacity of mitochondrial functions in cold adapted eurythermal species. As a consequence the cost of mitochondrial maintenance increases in the cold, costs of ventilation and circulation increase in due course, with less energy available for growth and reproduction. The lower growth rates with cold acclimation as well as with cold adaptation are in line with these physiological constraints. Temperature adaptation is linked to tradeoffs in cellular aerobic metabolism and energy budgets, causing consequences at the population level. Firstly cold-adapted Northern cod populations showed poorer growth at all temperatures reflecting permanent differences between populations. The statistical analysis of growth data and oxygen consumption rates showed that the acclimation temperature superimposes the influence of the phenotype on growth.
Summarising our results we could predict that global warming leads to a rise in growth performance and fecundity for northern populations and to a drop for populations living at the southern border of their distribution. Data modelling confirms this prognosis, predicting the disappearance of cod from their Southern distribution limits and also a decrease of total stock biomass. If warming extends to the Arctic, the loss of cod in the south will be compensated for to some extent by increased productivity in the North since warming in those areas will alleviate the trade-offs essential for cold adaptation but detrimental to high growth rates. These predictions are valid under the precondition that food availability and predatory pressure on the various life stages remain unchanged
The general objective of this proposal is to investigate the possible impact of climate induced temperature changes on the distribution and population dynamics of two fish species by evaluating the effects of the temperature regime on the physiological, genetic and ecological level. We have selected two model species which have their northern and southern distribution limits in the North Atlantic and the different populations of which have adapted to differing temperature regimes. Cod (Gadus morhua) represents the offshore species whereas the eelpout (Zoarces viviparus) is the coastal target.
The specific objectives of this proposal are related to the following tasks:
Ecological Studies: To identify effects of past, climate induced temperature changes on the distribution and population dynamics of cod and eelpout populations in North Sea, Baltic Sea, Norwegian Sea and Barents Sea by retrospective studies and to assess the influence of climate conditions on the population parameters of these species from different climate regions;
Physiological Studies: To determine the critical sublethal temperature limits of these species by identification and monitoring the temperature sensitive physiological key processes and to build up an energy balance;
Genetic Studies: To determine the adaptational potential of these species. Modelling To build up an integrated unitary model of the temperature-sensitive response of these species from the molecular to the population level. This combination of retrospective studies, field data analysis, physiological experiments, genetical investigations and modelling will further our understanding of the past and present impact of climate induced temperature changes on fish populations. The results will allow us to make better projections with respect to future anticipated global warming.
Funding SchemeCSC - Cost-sharing contracts