A novel expert-driven methodology to develop thermal response curves and project habitat thermal suitability for cetaceans under a changing climate

Abstract

Over the last decades, global warming has contributed to changes in marine species composition, abundance and distribution, in response to changes in oceanographic conditions such as temperature, acidification, and deoxygenation. Experimentallyderivedthermallimits,whichareknowntoberelatedtoobservedlatitudinalranges,havebeenusedto assess variations in species distribution patterns. However, such experiments cannot be undertaken on free-swimming large marine predators withwide-rangedistribution,likecetaceans. Analternative approach is to elicit expert'sknowledge to derive species' thermal suitability and assess their thermal responses, something that has never been tested in these taxa. Wedevelopedandappliedamethodologybasedonexpert-derivedthermalsuitability curvesandprojected future responses for several species under different climate scenarios. We tested this approach with ten cetacean species currently present in the biogeographic area of Macaronesia (North Atlantic) under Representative Concentration Pathways 2.6, 4.5 and 8.5, until 2050. Overall, increases in annual thermal suitability were found for Balaenoptera edeni, Globicephala macrorhynchus, Mesoplodon densirostris, Physeter macrocephalus, Stenella frontalis, Tursiops truncatus andZiphiuscavirostris. Conversely,ourresults indicated a decline in thermalsuitabilityfor B.physalus, Delphinus delphis, and Grampus griseus. Our study reveals potential responses in cetaceans' thermal suitability, and potentially in other highly mobileand large predators, andittests this method's applicability, which is a novel application for this purpose and group of species. It aims to be a cost-efficient tool to support conservation managers and practitioners.