Movement, diving and foraging success in a large, sexually dimorphic marine predator: Insights from telemetry

Establishing where and when predators forage is essential to understanding trophic interactions. Recently, the abundance of grey seals (Halichoerus grypus) in the Northwest Atlantic has raised concerns about the impact of predation on commercial fish species. However, current predation models are limited by assumptions that predation is constant in time and space. Therefore, the goal of my research was to examine the spatial and temporal scales of foraging in grey seals. Advances in telemetry make it possible to study diving, movement and distribution of feeding at sea. Given evidence of sex-specific differences in diving and energy storage in this body-size dimorphic species, I predicted that sex would be important in structuring foraging behaviour.; I examined the use of space by grey seals by quantifying movement patterns using locations from satellite telemetry. Using correlated random walk (CRW) and Levy Flight models, I found that individuals used three types of movement: those which followed a CRW, those which were over-predicted by the model and used Sable Island year-round (residents), and those which were under-predicted by the model and used larger-scale directed travel. Movement type was related to sex, with males more likely to exhibit directed travel. The failure of most to fit a Levy Flight suggested that prey were not randomly distributed. The temporal pattern of feeding success using stomach temperature telemetry revealed considerable individual variation, some of which was related to sex. The number of feeding events and average time associated with feeding was greater in males. By linking distribution and feeding success with dive data from time-depth-recorders, I investigated how feeding was related to both movement and diving behaviour. Foraging trip length, accumulated bottom time and angular variance were all predictors of successful feeding. Diving characteristics differed by movement type, independent of sex, such that residents had longer bouts and dove to shallower depths. My research demonstrated that although grey seals exhibited marked individual variation in movement, diving and feeding patterns, males and females differed both in the characteristics of feeding and the way they used space. These findings have implications for the way we model predation in marine ecosystems.