Forecasting the response of a recovered pinniped population to sustainable harvest strategies that reduce their impact as predators

Abstract

Abstract The recovery of marine mammal populations has led to increased predation on commercially valuable prey species, creating conflicts with fisheries and calls for predator control. Grey seals are important predators of Atlantic Cod and Winter Skate in the southern Gulf of St. Lawrence (sGSL), and both species are likely to be extirpated unless grey seal presence in that ecosystem is strongly reduced. We aimed to identify harvest strategies that reduced grey seal presence in the sGSL to levels that favour fish recovery while maintaining grey seal conservation goals. We fit an integrated population model to grey seal abundance, reproductive and mark-recapture data, and projected future presence in the sGSL while varying the magnitude and age-composition of the annual commercial quota. We found that both removal and conservation targets could be met with annual quotas of 6000 seals if 50% of hunted seals were young of the year (YOY), though small amounts of overhunting reduced seal abundance below limit reference levels. Harvest strategies that targeted higher proportions of YOY were less likely to trigger conservation concerns, though these strategies required much larger quotas to achieve removal targets.