SI2023 – A-16 – Factors Influencing Movement, Habitat Choice and Breeding Dispersal in Male Grey Seals (Halichoerus Grypus) on Sable Island, Nova Scotia – Nicole Harrington

Movement behaviours of male grey seals (Halichoerus grypus) within the breeding colony are indicative
of a polygynous female-defense mating strategy that varies largely according to competitive ability. As
such, males exhibit a sex-biased dispersal, with mating tactics broadly characterized by their movement
pattern; a tenured (single location defense, low movement) or transient (several locations and females,
high movement) tactic, or a combination of both. Male grey seal breeding dispersal and associated
movements may be a functional response to environmental (e.g., competition in habitat) and demographic (e.g., age, population density) factors, whose effects on the level of male movement during the breeding season, are largely unknown. This study investigated age, habitat choice and population density as hypothesized factors influencing male grey seal movement during the breeding season on Sable Island, Nova Scotia, using an established long-term database of repeated sightings of breeding male grey seals. Longitudinal sighting data were collected on 380 known-aged, permanently, and individually marked breeding males. The database had an age range covering the lifespan of the male grey seal, 4-35 years. Sighting data of male grey seals were collected during the breeding seasons (December to January) of 2004 to 2021 through weekly censuses of the entire colony. Most sightings of males on the breeding colony were between ages 19 and 23. Distance moved by each male between censuses showed large variability in movement across cohorts and among individuals, with a median movement distance of 2.5km. A Generalized linear mixed-effects model (GLMM) was used to examine the causal factors of male movement (i.e., age, and population size) where prime aged males were found to move less than young and old males, with long periods of tenure. High repeatability in individual movement variation (0.599, 95% CI [1.22-1.41]) was observed. Chi-squared tests found that males display habitat preference and differing habitat use between young and prime age groups. Identifying the factors driving male movement will provide an understanding of the relation between these movement patterns and variances in male mating success and fitness.

Nicole Harrington is a recent BSc graduate of Dalhousie, where she completed her honours research studying the movement patterns, habitat choice and breeding dispersal of male Grey Seals on Sable Island during the breeding seasons. Through this research, she spent the 2023 field season on Sable, assisting the DFO Grey Seal Team and visiting scientists with ongoing research, getting to experience first-hand the work she contributed to just the year before. Nicole‚Äôs research experience with Sable Island continues as she begins her master’s degree at Dalhousie this fall, examining Grey Seal diet.