Peruvian pinnipeds as archivist of ENSO effects off the coast of Peru

Environmental fluctuations in the eastern Pacific Ocean are reflected in the tissues of one of its most vulnerable apex predators, the Peruvian fur seal Arctocephalus australis . The coastal waters off Peru are a region of great environmental fluctuations due to periodic (every 2-7 years) El Niño-Southern Oscillation (ENSO) events, which result in ecosystem-wide food web changes. Pinniped body tissues reflect the incorporation of prey from the region, which can be evaluated using stable carbon and nitrogen isotope ratios (δ ¹³ C and δ ¹⁵ N). Continuously growing tissues, like vibrissae (whiskers), can potentially provide a large scale timeline of environmental data in an ecosystem where changes regularly occur and human instrumentation to measure such changes is sparse. Sea surface temperature (SST) anomalies along the Peruvian coastline are encompassed in the body of water known as Niño 1+2; a SST anomaly index used to categorize ENSO events. This region distinguishes itself from the more widely studied water bodies Niño 3, 3.4, and 4 by exhibiting more frequent and shorter-lived heating and cooling oscillations in SST. These oscillations appear to coincide with the δ ¹³ C and δ ¹⁵ N signatures recorded in the Peruvian fur seal vibrissae collected from 2010 (n=29), 2011 (n=12), 2012 (n=11) and 2015 (n=12). The δ ¹³ C and δ ¹⁵ N covary along the vibrissal length except for distinct points where their patterns are inversely related. These points are identified as transition periods between the region’s rapidly changing El Niño/La Niña phases. Adult female δ ^{1 3} C values throughout all sampled years (n=49), ranged from -18.13 to -13.19 ‰ ± 0.33 ‰. This reflects wide fluctuations in ocean production over time, which is our proxy to ENSO effects. Preliminary δ ¹⁵ N values range from 15.83 to 21.55 ‰ ± 0.85 ‰. These data suggest that these fur seals might be using alternative foraging survival strategies during these ENSO periods by foraging at two or more trophic levels. These may be the first biologic data of their kind to reveal how abiotic, ecosystem-wide changes influence the trophic dynamics and resultant survivability of the Peruvian fur seal.