Multidecadal changes in home range characteristics of grey seals in a context of environmental changes and population growth in the Northwest Atlantic

Most marine ecosystems are experiencing increasing cumulative impacts from climate change, fishing, shipping and land-based pollution. The resulting ecosystem responses are challenging to monitor. Studying the space use of top marine predators may provide insight into how these ecosystems react to these impacts. However, natural populations are composed of unique individuals that differ in many ways, including how they use space. Here, we used data from a multidecadal biotelemetry research program on grey seals in the Northwest Atlantic to investigate temporal changes in space use in the context of environmental changes and increasing population size. We quantified temporal changes in monthly home range size, shape and distribution of grey seals in the Gulf of St. Lawrence between 1992 and 2022, while also quantifying interindividual differences. We found that the monthly home ranges of grey seals have increased in size and shifted in distribution over the last 3 decades, indicating that the seals appear to have expanded their space use. We detected individual differences in mean home range characteristics and their level of variability, suggesting that individual identity plays a role in the large-scale space use of grey seals. We also found negative correlations between the mean and level of variability in both home range size and shape, hinting at the potential presence of different tactics within the population. This study highlights how top marine predators can modify their behaviour to adapt to environmental changes and illustrates the importance of considering interindividual differences when exploring population space use patterns.