Beaked whales and El Niño: evidence for ENSO effects on Blainville’s beaked and goose-beaked whale space use in Hawaiian waters

Large-scale climatic phenomena, like the El Niño-Southern Oscillation (ENSO) cycle, influence marine systems across the Pacific and beyond. The effects of these cycles on Hawaiian marine communities, particularly their impact on cetaceans, remains understudied. Using location data obtained from satellite tags deployed on Blainville’s beaked whales Mesoplodon densirostris and goose-beaked whales Ziphius cavirostris , and sightings data from 2 decades of surveys off the west coast of Hawai‘i Island, we examined the effects of ENSO, season, and 2 other climatic cycles on the space use and sighting rates of these species. Beaked whale sighting rates during El Niño phases were more than double those during La Niña periods, and every period of effort during Central Pacific-‘flavored’ El Niño conditions yielded sightings of both species. Seasonal variation in goose-beaked whale sighting rates was also found. Moreover, both species exhibited variation in space use between climatic phases, with goose-beaked whales displaying a higher propensity to use the windward side of the island after extended La Niña conditions. Shifts in prey availability or predation avoidance in relation to seasons or ENSO events may be the primary drivers behind these findings. More tagging and sighting effort will be necessary to confirm the level of cycle intensity at which these species respond to ENSO cycles, as well as which combinations of climatic phenomena most intensely influence their environment. Our results provide valuable insights for the potential of climate change to influence space use by beaked whales and other odontocetes.