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Galápagos sea lion (Zalophus wollebaeki, Sivertsen 1953)

Abstract:

The Galápagos sea lion (GSL, Zalophus wollebaeki) is the smallest sea lion species in the world, endemic to the Galápagos archipelago and formerly considered a subspecies of the California sea lion (Zalophus californianus). Breeding rookeries occur throughout the archipelago. Females are highly site faithful; hence genetic exchange between rookeries occurs predominantly through male dispersal. Females start their reproductive career rather late at a mean age of 6 years, give birth to a single pup, and nurse it unusually long for between 2 and 4 years. If a female bears another pup during lactation, the newborn's survival is seriously reduced. The extended period of maternal care lowers the reproductive rate to around 0.4 pups per adult female per year. Moreover, in years of strong El Niño events, pup mortality increases, and even older animals commonly die of starvation. Pups show distinct personalities such as shy and bold within their early social environment, thus shaping how they explore new situations and habitats. Once independent, diving strategies can also consistently differ between individuals: some forage via shallow dives, whereas others dive deep and/or mostly at night. Over the last 15 years, survival rates across all age classes have decreased in one important rookery located in the center of the species' distribution. Recent demographic models in the Caamaño rookery pbkp_redict substantial population decrease in the coming years, likely to be further exacerbated by increasing sea surface temperatures due to global warming and more frequent El Niño events. Low abundance within a small distribution area makes the GSL vulnerable to a combination of anthropogenic and stochastic environmental disturbances. Fishery interactions, pressures from increased tourism, and habitat intrusion along with the potential for introduction of diseases are presently great dangers which may pose a serious threat to this endangered species.