Spatiotemporal variation in pup abundance and preweaning survival of harbour seals (Phoca vitulina) in the St. Lawrence Estuary, Canada

Marine mammal populations worldwide greatly benefitted from conservation measures put in place since the 1970s following overexploitation, and many pinniped populations have recovered. However, threats due to bycatch, interspecific interactions or climate change remain, and detailed knowledge on vital rates, population dynamics, and their responses to environmental changes is essential for efficient management and conservation of wild populations. In this study we quantified pup abundance and survival of individually marked harbour seal (Phoca vitulina Linnaeus, 1758) pups during the preweaning period at Bic Island and Metis sites in the St. Lawrence Estuary from 1998 to 2019. We used mark-recapture models to evaluate competing hypotheses regarding variation in daily preweaning survival rates and capture probability during the pups' first 30 days of life. Pup abundance increased from 76 [95% CI: 59, 101] to 323 [95% CI: 233, 338] in the past two decades at Bic Island and from 66 [95% CI: 47, 91] to 285 [95% CI: 204, 318] at Metis. Preweaning survival was generally higher at Bic (0.73 [95% CI: 0.58, 0.82]) than at Metis (0.68 [95% CI: 0.52, 0.79]). We hypothesize that differences between habitats and human disturbance contribute to lower preweaning survival at Metis, but behavioural studies are needed to understand the impacts of disturbance on mother-pup interactions during the nursing period. Key words: abundance, Bayesian capture-mark-recapture models, harbour seal, marine mammals, Phoca vitulina, population dynamics
Introduction Identifying the factors driving changes in population growth, composition, and size is central to ecology (Krebs and Myers 1974; Krebs 1996, 2015). Population growth depends on vital rates, including [...]