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Resolving Climatic impacts on fish stocks

Final Report Summary - RECLAIM (Resolving Climatic impacts on fish stocks)

The oceanic conditions show decadal and multi-decadal oscillations that reportedly influence ecosystems and fish and are intensified by the recent global climate change. The implemented global circulation models (GCMs) predict an increase in air and sea temperature, changes in precipitation and loss of sea ice cover, while the effects of climate change on wind and storms are less certain. There is ample evidence that the primary and secondary ecosystems’ productivity will be affected by such alterations, even though the impacts’ extent will vary between different geographic regions.

The RECLAIM project studied the effects of the observed and expected climate change on the productivity and distribution of fish and shellfish populations and reviewed the strengths and weaknesses of current scientific knowledge in order to identify critical information gaps and provide sound advice, recommendations and working hypotheses for future research. The identified research agenda included six equally prioritised proposals. One suggestion was generic while the remaining five were specific, but necessary to fill critical information gaps.

RECLAIM included an extensive literature review of the ocean climate, marine ecosystems and fish population. The project exploited biophysical models to define the effects of modifications in radiation, temperature and winds. Patterns of change were identified by analysing biological time-series in relation to climatic variables. Moreover, a framework was developed to assist the mechanistic understanding of the processes, based on principles of physiology and ecology.

An important parameter for the evaluation of likely impacts of climate change was the eco-physiology of the various life history changes of different species. Climate warming was expected to be more detrimental for benthic animals than for pelagic species, with probable effects on fish depending on benthic prey types. In addition, substantial implications on fisheries were expected; nevertheless, further research was required to scientifically support this conclusion.

The project utilised GCMs to derive conclusions on the potential modifications in water salinity, temperature and acidification and in CO2 concentrations. However, GCMs were not capable of representing observed ocean oscillation patterns and finer modelling resolution had to be developed so as to improve simulation accuracy in the future. Moreover, research towards the creation of downscaling strategies for dynamic regional models was necessary to quantify the potential impacts on local biology. Finally, the uncertainties in regional projections had to be reduced.

An attempt to define the effects of fishing in primary ecosystems’ production was also undertaken for different areas. The occurrence of productivity changes was indisputable for all ecosystems; nevertheless the complexity of the influencing factors and their interrelations resulted in varying conclusions, depending on the different geographical conditions which in turn influenced most environmental parameters. Long-term ecosystem monitoring programs were highlighted as being essential for collecting useful data to thoroughly understand the involved processes.

Numerous evidence of the relation between climate and fish population was available during RECLAIM elaboration, even though the underlying mechanisms were not well known. A variety of methods was used to define fish life stages with maximum climatic sensitivity, including analyses of the abundance and mortality across successive growth stages. No common patterns were identified between the examined organisms; nevertheless it appeared that prey abundance, particularly during the late larval and early juvenile periods, was a critical environmental parameter. The adaptive capacity of fish and other organisms to changes in abiotic factors could mitigate the anticipated impacts; however, this capacity was largely unknown and had to be further investigated.

RECLAIM used nutrient, phytoplankton, zooplankton and detritus dynamics (NPZD) models to determine climatic influence on fish larvae and the simulation results were compared to observations’ data. Useful conclusions were derived for fish, as well as for plankton and benthic species. Moreover, a combination of NPZD and dynamic energy budget (DEB) modelling was utilised to approximate the completion of species’ life cycles. Future research attempts should focus on the likely consequences of changes to commercial fisheries and regional economies, which were not extensively analysed during RECLAIM.

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