Multiscale feeding ground fidelity in a migratory marine predator revealed by integrating satellite telemetry and stable isotopes

Marine megafauna are considered ecosystem sentinels because their distribution and demography reflect variations in prey availability and ocean productivity. Fidelity to feeding areas can therefore serve as an indicator of the long-term ecological importance and productivity of particular regions. However, assessing feeding ground fidelity in vast, open-ocean environments remains challenging, as feeding habitats are spatially diffuse and dynamic, and direct observational data are rare. Here, we investigate feeding ground fidelity in the New Zealand southern right whale ( Eubalaena australis ) population by integrating methods with complementary strengths and limitations: satellite telemetry and stable isotope analysis. We deployed satellite tags to track whales and used movement models to infer feeding behaviour and locations. We collected skin biopsy samples from the tagged whales, and measured tissue δ 13 C and δ 15 N isotopes. We then compared the isotope value from whale skin samples with baseline ocean phytoplankton isoscape rasters adjusted for trophic level to identify likely feeding ground associations. The whales exhibited short-term (interannual) fidelity to feeding grounds at two different spatial scales. Satellite telemetry revealed movement patterns that could be indicative of feeding behaviour across a broad region south of Australia, broadly aligning with population-level isotope assignments. At finer scales, individuals showed repeated use of highly localised sites that could represent important feeding areas. Together, these results provide direct evidence of multi-scale feeding ground fidelity in southern right whales, likely reflecting a combination of maternally transmitted migratory patterns and more flexible, short-term responses to environmental or prey-driven cues. Our findings highlight the value of integrative approaches for detecting feeding ground use and fidelity in open-ocean systems, with important implications for identifying and protecting ecologically important feeding habitats in areas beyond national jurisdiction.