Spatial richness patterns of large pelagic fishes in the Eastern Pacific Ocean

In the Eastern Pacific Ocean, the purse seine tuna fishery targets skipjack, yellowfin tuna, and bigeye tuna. However, bycatch of billfish is also common. Growing concerns about the rising bycatch levels and the capture of juveniles' tunas underscore the need for spatial explicit management strategies. This study aims to model the geographic distributions of four tuna species (skipjack, yellowfin, bigeye, and black skipjack) and five billfish species (swordfish, sailfish, striped marlin, blue marlin, and black marlin) to understand how interannual variability shapes richness patterns of these species to inform spatial management efforts. Species distribution models were developed using MaxEnt based on environmental scenarios representing cold, neutral, and warm conditions from 2000 to 2020. A database of occurrences was compiled from Inter-American Tropical Tuna Commission's, while environmental variables were obtained from Copernicus Marine Service. Predicted distribution maps for each species were combined to generate species richness maps under different environmental scenarios. Areas of high species richness were identified near the Baja California peninsula, the southern Gulf of California, off the coast of Central America, and between the Ecuadorian coast and the Galapagos Islands, regions that overlap with known spawning and feeding grounds. Species richness patterns showed an interannual variability, expanding during warm periods and contracting during neutral and cold conditions, highlighting the need to adapt spatial management to environmental variability of oceans. These findings provide a basis for future spatial planning and conservation initiatives, highlighting the need for dynamic, flexible conservation strategies that can adapt to a changing ocean.