Distribution of herring (Clupea harengus) and zooplankton in the Norwegian Sea, as determined from generalised additive models

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We analyse the variability in the distribution and feeding of the Norwegian spring-spawning herring in the period from 1995 to 2004, using survey data collected throughout the Norwegian Sea each year in May - June. The spatial component is handled by fitting generalised additive models (GAMs) to the data. GAMs are an extention of generalised linear models, allowing flexible nonparametric effects of covariates such as latitude and longitude. We also describe the spatial and temporal variability in zooplankton biomass, water temperature and salinity. The data suggest that both herring body size, stomach fullness and zooplankton biomass was higher in the western part of the ocean basin, and that herring generally had a relatively wide and patchy distribution.