Estimating spatial mixing within the St. Lawrence Estuary beluga population by comparing local individual diversity and abundance

Abstract

Interindividual variability in habitat preferences affect local abundance and residency times. Within a population range, this can lead to sectors having a continuous flow of unique individuals, with others being used by the same set of resident individuals. These patterns of habitat use by individuals, referred to here as individual spatial mixing, can have important implications for ecological and evolutionary processes. This study proposes a novel approach for estimating the degree of individual spatial mixing in an endangered beluga population, based on the comparison of local individual diversity obtained from photo-identification data against abundance indices derived from systematic aerial surveys. Divergences between long-term indices of abundance and diversity were observed across many sectors within the population's summer habitat. This was the case notably for the Saguenay Fjord, where on average only 1.8% of the total population count was detected during summer aerial surveys, but where 41% of all individuals identified in the photo-identification data were found at least once. The comparative approach proposed in this study to estimate individual spatial mixing can help quantify site fidelity patterns in wildlife populations and estimate its vulnerability to local stressors such as anthropogenic noise.