Guadalupe fur seal pup production predicted from annual variations of sea surface temperature in the southern California Current Ecosystem

Abstract

We evaluated the effects of sea surface temperature anomalies (SSTA) in the southern California Current Ecosystem on the annual Guadalupe fur seal (Arctocephalus townsendi) pup production, a species recovering from near extinction. Pup counts from 1991 to 1993 and from 2006 to 2019 were used to estimate deviations from a long-term trend as a proxy for the population's reproductive success. We estimated interannual SSTA as a subtraction from the linear trend spanning 1991-2019 for a 778,000 km2 area, which represents the primary foraging range of adult females. The long-term increase in pup production followed an exponential curve (R-B2 = rm), typical of species in a recovery phase. Pup production deviations from this trend responded to SSTA during the gestation period as a cubic polynomial function (R-B2 = rm 0.837), revealing that SSTA < -0.2°C and between ∼0.6 and 1.38°C increased pup production in the subsequent breeding season, whereas normal to slightly warm (-0.17 to 0.6°C) and extreme SSTA (>1.4°C) decreased pup counts, arguably resulting from low prey availability and quality. This model allowed us to estimate pup production for years without observations, needed to understand the environmental variability influence on the recovery process of this species, and therefore constitutes a practical tool for its conservation and management.