ENSO-driven distribution shifts in the critically endangered Mustelus whitneyi along the Northern Peruvian Coast

Mustelus whitneyi (humpback smooth-hound shark) is a Critically Endangered demersal species endemic to the southeastern Pacific and exploited by small-scale fisheries in northern Peru. This study evaluated how seasonal and interannual environmental variability, particularly associated with the El Niño-Southern Oscillation (ENSO), influences the spatial distribution of the species. Presence-only data collected between 2015 and 2018 were combined with six oceanographic variables selected from an initial set of eight candidate predictors from the Copernicus Marine Service to develop seasonal species distribution models (SDMs) using Maxent. To account for sampling bias associated with fisheries-dependent records, background selection was informed by a distance-based bias raster. Models performed better than random expectations in all scenarios, although performance varied among seasons and several models exhibited elevated omission rates, indicating lower predictive reliability during specific periods. Bottom potential temperature emerged as the primary environmental predictor, highlighting the importance of subsurface thermal conditions for this demersal species. Predicted suitable habitat showed seasonal and interannual variability. The largest predicted distribution areas were observed during El Niño conditions, particularly in austral spring 2015 and winter 2016, coinciding with warmer bottom waters. In contrast, neutral conditions in 2017 were associated with a contraction of suitable habitat during austral summer, whereas La Niña conditions in 2018 produced more fragmented spatial patterns. Overall, the results suggest that climate-driven environmental variability influences the spatial extent and configuration of the predicted distribution for M. whitneyi. This study provides the first ENSO-phase-specific SDMs for the species and offers a baseline for incorporating environmental variability into fisheries management and conservation planning in the Northern Humboldt Current System.