Effects of warm oceanographic anomalies on the foraging variability of northern elephant seals

Evaluation of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in marine organisms over time addresses how environmental variability (e.g., El Niño or The Blob) affects habitat use and food resources, respectively. This work focuses on the impact of warm events in the Northeastern Pacific Ocean on the foraging strategies of adult female northern elephant seals (Mirounga angustirostris; NES) from the San Benito Archipelago in Mexico during their post-molting migration, through isotopic variability in pups as maternal indicators. Analysis of δ¹⁵N and δ¹³C was carried out on lanugo samples (n = 311) of weaned pups from the 2013–2017, 2019, and 2022–2023 breeding seasons and correlations with sea surface temperature (SST) anomalies of the potential foraging areas of female NES from the San Benito Archipelago were investigated. Isotopic niches showed high overlap throughout most of the study period, suggesting a limited impact of SST anomalies on their foraging strategies. However, values of δ¹⁵N and δ¹³C differed in 2014, 2018, and 2021 relative to other years, suggesting shifts to distant regions in latitude and longitude, and increased foraging effort during the post-molting migrations of these warm years. Findings demonstrate the flexibility and adaptive capacity of female NES relative to the warm events of the last decade.