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MARINFORSK-Marine ressurser og miljø

ECOsystem dynamics in the NORwegian SEa - new methods for understanding recent changes

Alternative title: Nye metoder for økt forståelse av endringer i Norskehavsøkosystem

Awarded: NOK 8.3 mill.

The primary objective of project EcoNorSe was to improve our understanding about the interactions and the dynamics of the Norwegian Sea ecosystem by developing and using modern methods for identifying and quantifying the diet of these ecologically and economically important pelagic fish populations. At the beginning of the project, a set of ambitious goals was set with most of them achieved with its completion. The detailed sampling carried out during the scientific cruises has provided us with a unique data set that combines information on both the short- and long-term dietary habits of the main pelagic stocks in the Norwegian Sea, comprising the lipidic composition, stable isotopes concentrations in fish tissues and fish prey tissues and direct observations of fish stomach content items. Additionally, the concurrent sampling of the surrounding feeding environment provided us with indispensable information on possible selectivity on specific prey, thus allowing the extraction of conclusions on the feeding habits and interactions of these species under changing climatic and anthropogenic pressure scenarios. Modelling work on the drivers of spatiotemporal distribution of Atlantic mackerel, as well as bioenergetics modelling of the annual consumption of zooplankton by pelagic fish feeding in the Northeast Atlantic, have already utilised both past data and data collected during the surveys that took place during of the EcoNorSe project. In the first of these two studies, we identified the main drivers that affect mackerel's distribution in the entirety of the Nordic Seas. The temperature in the upper part of the water column, along with food availability and the concurrent presence of herring, seem to regulate mackerel's distribution, whereas density-dependence did not seem to be directly affecting the species' distribution. The second publication addressing EcoNorSe questions revealed that the three pelagic fish species consume higher zooplanktonic biomass than estimated in the past, as calculated by a bioenergetics model. In particular, mackerel and herring require approximately ten times their biomass in prey to sustain the observed growth levels, while blue whiting requires around six times its biomass. Despite these numbers, the ability of the three fish species to diversify their diet allows them to coexist in the Norwegian Sea. Finally, there is an ongoing analysis that is exploring the changes in biomass of the Norwegian Sea ecosystem components, using end-to-end ecosystem model simulations, based on the observation that mackerel has expanded its spatiotemporal distribution in the area. The main question to be addressed with this analysis is whether the increased presence and biomass of this ecosystem component (mackerel) in the area exerts significant pressure that affects the biomass of other ecologically and economically important ecosystem components (e.g. herring). Due to unforeseen setbacks in the samples collection, the progress in publication of data regarding the trophic interactions of the pelagic fish species has been somewhat slow, also due to the inherent complexity of combining this diverse information soundly. However, these setbacks were tackled in time and in the final meeting of the project, the necessary collected samples had been analysed. In that final meeting, detailed plans for at least four publications that will make use of the dietary information collected, as well as of new information available in scientific literature during the project's period, were made. We have already presented some results in peer-reviewed scientific publications and conferences, but more are expected in the years to come. The project's activity was presented to a broader audience through the project's webpage ( and electronic media (,

EcoNorSe results are an excellent basis for further studies of trophic interactions in the Nordic Seas, as the international cooperation achieved allows the results to impact research throughout the Nordic Seas and the Bay of Biscay, rather than only the Norwegian Sea. New and updated information on diet matrices provided by lipids, stable isotopes and genetic information, as opposed to the snapshot information derived by stomach contents analysis, will be highly important for improving bioenergetic modelling studies. The published results from EcoNorSe, have already served as input for DYNAMEET, a joint workshop funded by NFR, that promoted collaboration between EcoNorSe and the ICES Working Group on the Integrated Assessment of the Norwegian Sea. Finally, another important outcome was that the post doctor employed in EcoNorSe developed skills and qualifications with which he obtained a researcher position at IMR.

The ecosystem in the Norwegian Sea has been under constant change during the last decades. Ecologically and commercially important pelagic fish stocks have all had their turn in being the most abundant pelagic species, but the exact nature of the interspecific interactions between these species is still poorly understood. In the last decade the NEA mackerel stock has been expanding drastically. While mackerel stock is thriving, NSS herring stock is currently low and keeps on declining due to lack of successful recruitment since 2004. Some hypothesize that the absence of strong year classes of NSS herring is a direct result of expansion of mackerel as they prey upon herring larvae, but practically no quantitative evidence to evaluate this hypothesis exist (see however Skaret et al. in prep). In addition to the suggestion that mackerel are the cause of reduced prey levels (zooplankton) for species such as herring, it has also been hypothesized that by eating herring larvae (a preferred prey for some bird species), the mackerel would worsen the already dire conditions of many sea bird populations along the Norwegian coast. In the spirit of ecosystem based fisheries management the supposedly detrimental effect of mackerel on other fish stocks and sea birds should be taken into account in the management of the Norwegian Sea Ecosystem. In this study we aim at improving our understanding about the species interactions and the dynamics of the Norwegian Sea ecosystem by developing and using modern methods for identifying and quantifying the diet of these ecologically and economically important pelagic fish populations. We will use modern statistical methods to scrutinize these data, and end-to-end ecosystem models to test the hypotheses regarding ecosystem dynamics from plankton, via fish, to sea birds under the current climate change. This project is an investment in understanding and long-term monitoring and management of the Norwegian Sea and other ecosystems.

Funding scheme:

MARINFORSK-Marine ressurser og miljø