Quantification of trophic interactions in the Norwegian Sea pelagic food-web over multiple decades.

• Main Authors: Planque, Benjamin, Favreau, Aurélien, Husson, Bérengère, Mousing, Erik, Hansen, Cecilie, Broms, Cecilie, Lindstrøm, Ulf, Sivel, Elliot
• Format: Article in Journal/Newspaper
• Language: English
• Published: Zenodo 2021
• Subjects: Linear inverse modelling; herring; mackerel; blue whiting; copepods; krill; amphipods; Norwegian Sea,; competition; Norwegian Sea; Copepods
• Online Access: https://dx.doi.org/10.5281/zenodo.5710848; https://zenodo.org/record/5710848

While ecosystem-based fisheries management calls for explicit accounting for interactions between exploited populations and their environment, moving from single species to ecosystem-level assessment is a significant challenge. For many ecologically significant groups, data may be lacking, collected at inappropriate scales or be highly uncertain. In this study, we aim to reconstruct trophic interactions in the Norwegian Sea pelagic food-web during the last three decades. For this purpose, we develop a food-web assessment model compatible with existing observations and knowledge. The model is based on inverse modelling and is designed to handle input observations and knowledge that are uncertain. We analyse if the reconstructed food-web dynamics are supportive of top-down or bottom-up controls on zooplankton and small pelagic fish and of competition for resources between the three small pelagic species. Despite high uncertainties in the reconstructed dynamics, the model results highlight that interannual variations in the biomass of herring, mackerel and blue whiting can primarily be explained by changes in consumption rather than by predation or fishing. Variations in the biomass of copepods and krill were also linked to variations in consumption, while the past dynamics of amphipods can be explained by both consumption and predation. The model results provide little support for the hypothesised competition for resources between the three small pelagic species, despite their overlapping diets. We conclude that it is unlikely that the assessment and management of these commercial stocks during the last 30 years would have benefited from explicit incorporation of trophic interactions.