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Sensitivity of the fish community to different prey fields and importance of spatial-seasonal patterns

Karen E. van de Wolfshaar*, Ute Daewel, Solfrid Sætre Hjøllo, Tineke A. Troost, Markus Kreus, Johannes Pätsch, Rubao Ji, Marie Maar

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ABSTRACT: Different fish species and life-stages not only depend on food abundance, but also on the size of planktonic prey, and (mis-)matches in time and space with suitable prey may influence growth and survival of fish during their lifetime. We explored the sensitivity of a fish community to spatial-temporal differences in plankton prey fields. Data from five different lower trophic level models in the North Sea (Delft3D-WAQ, ECOHAM, ECOSMO, HBM-ERGOM, and NORWECOM) were used to force the food web model OSMOSE that simulates spatially and temporally explicit higher trophic level fish dynamics. The estimated fish biomass levels were clearly and positively linked to the zooplankton biomass, and sensitivity studies with varying zooplankton biomass revealed that spatial and temporal variation in zooplankton drives the differences in absolute fish biomass. More zooplankton size bins resulted in less fish biomass due to size-based foraging constraints (i.e. a smaller proportion of bins falls within the prey size range of a fish, resulting in a decrease in available food). Nevertheless, we found a consistent response across models in the relative biomass contribution and spatial patterns of selected fish groups, indicating a low sensitivity of the composition of the simulated fish community to the zooplankton input. The robustness of the outcome will aid model acceptance and implementation into management action. Relative, not absolute, changes in primary and secondary production may therefore be used to study effects of management scenarios on the fish community.