Habitat fidelity of adult grey seals over multiple years in a changing marine ecosystem.

backgroundIndividual foraging site fidelity is a common mechanism for dealing with environmental variability across marine predator species. However, there has been little research on long-term individual repeatability to date, especially over time periods where significant environmental and ecological change has occurred. The grey seal is a long-lived pinniped species that forages on the Scotian Shelf and in the Gulf of St. Lawrence, two ecosystems which are characterized by spatio-temporal variability in oceanographic conditions and have also undergone dramatic changes to ecological structuring and functioning in recent decades.

methodsBetween 1995 and 2018, 22 adult grey seals (17 females, 5 males) were repeatedly instrumented with tracking devices in two or three different years. We fitted continuous-time correlated random walk state-space models to estimate grey seal locations and move persistence along tracks. We then calculated the kernel utilization distribution overlap for home ranges (99%) and core areas (50%) within and between individuals as well as for areas (95%) associated with apparent foraging behaviour (move persistence < 0.5).

resultsHere, we show that grey seals demonstrated long-term moderate to high levels of fidelity in home ranges between years. By contrast, there was little between-year overlap in core areas used. Nevertheless, areas associated with low move persistence, inferred as area-restricted search and hence where foraging maybe more likely, were highly consistent between years. Habitat overlap between individuals was low across years.

conclusionsHome range fidelity appears to persist over the life of grey seals, despite significant environmental and ecological change occurring within their habitat during our study period. These findings contribute to understanding the potential consequences of projected environmental change for this and other central place foraging species.