Fine‐scale habitat use of foraging sperm whales is driven by seafloor topography and water column structure

Abstract

Knowledge of the spatial distribution and habitat preferences of marine top‐predators is essential for monitoring their populations. The summertime abundance of male sperm whales (parāoa, Physeter macrocephalus) at the Kaikōura Canyon (New Zealand) has almost halved over the last three decades, possibly reflecting a shift in distribution away from this foraging ground. To better understand the seasonal drivers of habitat use by sperm whales, we recorded presence and absence locations of foraging whales during acoustic‐visual surveys, in conjunction with water‐column oceanographic sampling. Season‐specific generalized additive models (GAM) indicated that whale distribution was best predicted by seafloor depth, thermal stratification in the water‐column, and slope gradient and orientation. Habitat use differed between summer and winter, consistent with patterns in diving behavior and stable isotope ratios, suggesting seasonal fluctuations in prey targeted by sperm whales. Our results advance understanding of fine‐scale habitat use by sperm whales, with new insights into the ecological drivers of seasonal fluctuations in foraging distribution. Our study demonstrates the importance of quantifying water‐column processes in the study of habitat preferences by deep‐diving predators. We also identify thermal stratification as an oceanographic feature susceptible to climate change, which could contribute to the decline in sperm whale abundance at Kaikōura.