Shifts in the habitat suitability for large hammerhead sharks under climate change

One of the chief consequences of climate change is the worldwide redistribution of species in the pursuit of physiologically and ecologically favourable conditions. As part of one of the most threatened groups of vertebrates, assessing how climate change may affect the distribution patterns of key shark species is essential for their long-term conservation and management. The present study aims to assess how climate change projections (based on the representative concentration pathways 2.6, 4.5, 6.0, and 8.5) for the middle and end of the century may affect the global patterns of habitat suitability (HS) for large hammerhead sharks – a unique and particularly threatened group of elasmobranchs. Here, a decline in the global average HS is projected for both Sphyrna lewini and Sphyrna zygaena, with the scale of HS decline generally increasing with time and RCP severity, while a global increase in HS is generally projected for Sphyrna mokarran, albeit reduced over the long-term and overturned under long-term RCP8.5. Meanwhile, poleward shifts are projected for all three species, with considerable tropical declines for both S. lewini and S. zygaena. Additionally, regional shifts in suitability have the potential to affect population connectivity, the access to key habitats, and levels of exposure to other anthropogenic pressures, along with the effectiveness of conservation and management efforts. Taken together, these results showcase the importance of climate change for species’ extinction risk assessments and the urgency of the consideration of climate change within the design and implementation of conservation measures.