Declining Abundance and Variable Condition of Fur Seal (Arctocephalus forsteri) Pups on the West Coast of New Zealand’s South Island

Abstract

New Zealand fur seals (Arctocephalus forsteri) were severely exploited by historical hunting. However, recently assessed colonies in New Zealand are mostly thought to be growing or stable. The exceptions are three colonies (Wekakura Point, Cape Foulwind and Taumaka Island) on the West Coast of the South Island (‘WCSI’), previously documented as in decline. We used mark-recapture and morphometric data to update understandings of pup abundance and condition at these colonies. Pup abundance has continued to decline. In 2025, 186 (95% CI = 178–194) pups were estimated at Wekakura Point, 131 (95% CI = 122–140) at Cape Foulwind and 566 (95% CI = 555–577) at Taumaka Island, representing declines of 83%, 71% and 61% from the respective maxima in the 1990s. Rates of decline have slowed at Wekakura Point and Cape Foulwind since 2016 but have increased at Taumaka Island. Pup condition demonstrated substantial interannual variation. Cape Foulwind pups had the greatest average mass and body condition index score, followed by Wekakura Point and then Taumaka Island. There have been consistencies between years of particularly low pup abundance and condition across the colonies, suggesting common stressors; however, there are likely also some localised factors. Emerging diseases and marine environmental change are evaluated as potential drivers.