Functional responses of a medium-ranging marine predator highlight the importance of frontal zones as foraging locations

Abstract

The distribution of marine predators is linked to bio-physical processes that structure the spatio-temporal availability of prey species. Within shelf seas, tidal fronts are highly productive regions occurring at the interface between mixed and stratified waters. Fronts are predictable but dynamic features, with their timing and strength varying seasonally and annually. The availability of frontal habitats will also vary between animal populations depending on geographic location. Thus, understanding the associations between marine predators and frontal habitats across a range of environmental conditions will assist marine management and conservation. Here, we assessed functional responses of breeding black-legged kittiwakes Rissa tridactyla to environmental covariates related to tidal fronts (front strength, distance to fronts, sea surface temperature [SST] and surface chlorophyll concentration) from 10 UK colonies located throughout the North Sea. Kittiwakes showed a tendency to forage in areas of higher, but not maximal, front strength when such areas were available. Areas closer to fronts (<10 km) were selected when available, though we also observed increased usage of areas distant from fronts (30-50 km). Kittiwakes tended to forage in cooler, mixed waters, particularly as average SST rose. When average chlorophyll concentrations were low, habitat usage peaked in areas of higher chlorophyll. The results highlight the importance of frontal habitats and the dynamic, non-linear nature of seabird responses to habitat. Accounting for dynamic changes in habitat availability will play a key role in future conservation efforts, particularly as marine renewable installations and climate change may influence water stratification patterns.