Foraging efficiency in diving predators based on prey availability : determining how prey schooling patterns and behaviour affect foraging strategies in two alcid divers

Seabirds worldwide are under great pressure from overfishing, habitat loss, predation, disturbance and climate change, evident in the rapid decrease of their population sizes. To conserve these numerous species, the need to share resources have become central, where especially human competition over commercially sought prey species has been pointed out as a key issue. Although the foraging behaviour of seabirds have been extensively researched over the last half century, few studies have had the opportunity to simultaneously study the prey availability as well as predictability of availability. In this essay, I will provide the theoretical framework and knowledge gaps that gives the foundation for my Ph.D. thesis. Thus, the essay will go into detail on topics concerning seabird movement (as monitored using global location/position sensors and dive movement recorders) and the available prey stock dynamics (by echo sounder equipped autonomous sail drone and research vessel), to describe the effect of schooling behaviour on two alcid species foraging efficiency. Firstly, I will describe how schooling behaviour is known to be affected by biotic and abiotic factors concerning the fish itself (e.g. species, biomass, time of day/season, predators present). Secondly, I will explore which factors in schooling behaviour that influence foraging efficiency in diving seabirds the most and how, determining the keys to availability of prey dependent on distance for central place foragers. Third, I will discuss the micro-migration and foraging conditions outside breeding season and during the critical onset of breeding. Finally, I will outline possible effects of increased fishery, competition and climate change by changing variables in the fish school behaviour equations. I review relevant literature on the study species; two closely related seabirds, razorbills Alca torda and common guillemots Uria aalge, and their main prey species, sprat Sprattus sprattus, herring Clupea harengus and three-spined stickleback Gasterosteus aculeatus. The alcid species forage on the same prey species in partly overlapping areas, but with different physiological adaptations affecting preferred flight distance and dive depth. This gives a great opportunity to explore species variations in response to changes in a common foraging environment.