Maternal flexibility in Galápagos sea lions mitigates climate impacts but not population decline.

The Galápagos sea lion is an endangered marine apex predator that has experienced a 50% to 75% population decline over the last 50 yr. Using 21 yr of data, we present the first long-term analysis of pupping trends and pup survival in this species, revealing how extreme climate oscillations may shape population dynamics and future trends. We found that the Caamaño colony has been in decline since monitoring began in 2003, with the rate accelerating significantly after the 2010 reproductive period. This pattern cannot be explained by climate effects or reduced female fecundity but is more likely the result of decreasing recruitment due to lowered juvenile survival. Although there has been no overall change in median pupping point date, there has been a significant shortening of the duration of the pupping period since the acceleration of the population decline. We found that maternal foraging strategy has a significant effect on pupping timing, and its interaction with resource availability causes further interannual variation in timing. Male pups are born significantly earlier suggesting sex differences in gestational length or implantation. Although climate does affect pup survival to yearling age, there has been no temporal change in survival over the study period. Body condition at birth and juvenile presence within the colony have a positive impact on pup survival. Our results reveal that Galápagos sea lions exhibit resilience to the extreme climate variability of their environment through reproductive plasticity around parturition and that their continued decline is likely driven by reduced recruitment and increased juvenile mortality.