Studying spatial and trophic interactions between capelin and cod using individual-based modelling

Abstract

The objective of this study was to use spatially explicit individual-based models for simulating the movement, foraging, growth, and mortality of cod and capelin in the Barents Sea in order to identify general features in their migration patterns and the consumption of capelin by cod. The individual-based models are initiated from survey data run over 1 year and validated against survey information. Directed movement is based on a combination of movement vectors and temperature boundaries, and bioenergetics models are used to calculate growth. Capelin consumption by cod is calculated from local encounters between the species. For capelin, the best movement model can be summarized as: stay southwest of the 2.5°C and 4°C temperature front at 50-m depth for juvenile and mature individuals, respectively, in winter, and migrate northwards during summer, but do not pass the −1.5°C temperature front. The best cod model was to migrate south-southwest during winter and north-northeast during summer, within the temperature range 1°C to 8°C. The annual consumption estimates found here reflected the interannual and seasonal pattern from previous studies based on stomach samples, but were generally lower. Consumption estimates varied depending on the movement models, and the best movement model also produced the consumption estimate closest to that obtained in other studies. Introducing a simple rule stating that cod should move in a randomly selected direction when the local capelin density is zero increased the consumption estimate by 30%. This suggests that more emphasis needs to be put on exploring how behavioural rules in predators and prey affect their interactions. Even though there are some discrepancies between predictions and observations, the results achieved by the model with regard to spatial distribution, growth, and consumption are promising.