Present and future hotspots for basking shark encounters along the northern Northeast Atlantic coast

Sammendrag

Effective conservation and management require detailed knowledge about a species’ distribution and habitat preferences. The endangered basking shark (Cetorhinus maximus) faces pressures from maritime traffic, pollution, incidental bycatch, and climate change, yet fundamental information about its habitat use is limited, especially in the northern parts of its range. Using recently compiled citizen science observations from Norway and the British Isles, we fitted Boosted Regression Tree models to identify areas with high probability of basking shark encounters in surface waters along the northern Northeast Atlantic coast. The results indicated that the probability of encountering basking sharks in surface waters decreases as bottom depth increases, temperatures fall below 8–9°C, and chlorophyll concentrations are relatively low. Projections based on future climate scenarios suggest a northward shift in basking shark distribution, leading to reduced encounter probabilities off the southwestern coast of England and the mid-Norwegian coast, and increased encounter probabilities along the northern Norwegian coast and into the Barents Sea. We further fitted a detailed species distribution model within one of the areas with a high encounter probability, the Lofoten and Vesterålen archipelagos in Northern Norway. Here, the probability of encountering basking sharks was higher in convergence zones and areas with high zooplankton biomass in the upper water column. These findings can be used to highlight relevant areas for field efforts and where conflict with human activities is likely.