Abiotic Stressors Expose Peruvian Fur Seal Parental Care

Vulnerable Peruvian fur seals (PFS) Arctocephalus australis are genetically isolated subspecies of South American fur seals and have a major breeding colony in Punta San Juan, Peru. PFS display strong site fidelity on densely populated rookeries, likely due to their highly productive foraging environment associated with upwelling. PFS are susceptible to strong environmental fluctuations known as El Niño-Southern Oscillation (ENSO) events, evidenced by sea surface temperature anomaly (SSTA) fluctuations in the Niño 1+2 index. Fur from 2009 (15 adults, 28 pups), 2010 (28 adults, 27 pups) and whiskers from 2015 (6 dam-pup pairs) are comprised of keratin and are isotopically comparable. Stable carbon and nitrogen isotope ratios (δ ¹³ C and δ ¹⁵ N) were employed to detect patterns in foraging habits and how they are reflected in pup tissues. The difference in δ ¹⁵ N between adult females and pups was no more than 0.8‰ in all three years, and both age classes had an average overall decline of 1.6‰ from 2009 to 2015. This is in contrast with δ ¹³ C; females in 2009 and 2015, as well as pups, had nearly identical values. The 2010 adult δ ¹³ C were significantly more enriched by 0.8‰ compared to the other two years, likely indicative of a more productive food web. The adult fur represents growth during the peak of the 2010 moderate La Niña phase (a cooler, productive period), while the pup lanugo, depleted by ~0.5‰ compared to the two other years, was grown during both the ENSO normal and moderate La Niña phase. The lipid-rich diets consumed by the dams of these pups may have provided additional lipid during critical fetal growth that would be represented in depleted δ ¹³ C exhibited in the pup fur. The combined isotopic data from foraging adults and their developing fetuses provide finer-scale resolution of the effects of ecosystem change than population estimates.