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Are fish populations and ecosystem dynamics shrinking in the Norwegian Sea
Published:  17 September, 2012

THE NORWEGIAN SEA is home to many different species of fish. Of them, the Norwegian Spring-Spawning Herring, blue whiting and the Northeast Atlantic mackerel make up what is known as the ‘pelagic complex’. All three species are planktivorous and inhabit similar parts of the sea.

It follows that the three species could have considerable effects on each other as well as on the ecosystem itself – but just how much?

The question is answered in the current issue of Marine Biology Research (8:5–6 [2012]).

An international team of researchers from the INFERNO project (2006–9), many of whom were from the Norwegian Institute of Marine Research, set out to address the hypothesis that the planktivorous fish populations feeding in the Norwegian Sea have interactions that negatively affect individual growth, mediated through depletion of their common zooplankton resource. In other words, is the size of fish reduced when there is more competition for a depleted resource?  

During the period in question, there was a downward trend in zooplankton biomass, meaning less food for all fish. Changes in fish-migration patterns, temperatures, horizontal and vertical distribution, variability in the abundance of food as well as seasonal and lifecycle trends in feeding also had the potential to affect the three species.

The studies confirmed the original hypothesis: ‘all the stocks showed signs of density-dependent length growth, whereas for herring and blue whiting there were also significant effects of interspecific competition.’  

As a result of the nine papers and related research presented in this special issue, marine scientists will not only have a better idea of what’s happening under the waves of the Norwegian Sea, but also how future trends can be predicted.

Several of the papers address the use of 3D and Individual-Based Models (IBMs) to estimate the horizontal and temporal overlap of fish and the amount of food they might consume. As the authors note, the models can be widely applied: ‘Individual-based ecosystem modelling systems try to thoroughly integrate differences among species, populations, size/year classes, and habitats in temporally and spatially dynamic algorithms aiming at generating predictions on larger-scale ecological processes and changes.’

Although the specifics of the data and the modelling presented relate to the Norwegian Sea, the authors intend that their work should reach a wider audience, firmly believing that it ‘may represent a very valuable example of what could be applied in many other marine ecosystems’.

The authors also feel that ‘it will be important to include these findings in the future ecosystem based management of the Norwegian Sea’; this special issue of Marine Biology Research is thus essential reading for conservationists, marine biologists and anyone with an interest in commercial fisheries or the northern seas.

Read the full editorial published in Marine Biology Research online now:

Download the entire special issue ‘Effects of interactions between fish populations on ecosystem dynamics in the Norwegian Sea - results of the INFERNO project’ now:

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