Abundance estimates of Fraser’s dolphins (Lagenodelphis hosei) in Hawaiian waters exceed 40,000 individuals, yet the species is rarely encountered near the main Hawaiian Islands (MHI). To assess whether this apparent rarity reflects limited survey coverage or actual infrequent use of near-island habitats, we analyzed 167,229 km of effort and sighting data from 27 years (1999–2025) of small-vessel effort around the MHI. Fraser’s dolphins were only encountered 10 times off Hawaiʻi Island and once near Kauaʻi. Citizen science sightings have also been documented off O‘ahu. Restricting effort to just Hawaiʻi Island in conditions suitable for detection (depth >1,000m; sea state≤4), 99.1% of effort days and 79.2% of survey years yielded no sightings, with sighting rates peaking between winter and spring. No encounters occurred during El Niño conditions. All sightings were associated with positive daily SST anomalies (≥0.35°C) except a single 2012 encounter during a pronounced negative anomaly, which also represented the shallowest and closest-to-shore sighting off Hawaiʻi Island. Seafloor depth at encounters indicated that the highest sighting rates occurred in depths ≥3,500m, despite comparatively limited survey effort there. Nearly all encounters featured large, tightly aggregated groups exhibiting boat-avoidant behavior and associating with melon-headed whales (Peponocephala electra). Three sightings off Hawaiʻi Island were of a lone individual closely interacting with pantropical spotted dolphins (Stenella attenuata). Citizen science sightings of this distinctive individual suggest the association has persisted from at least May 2024 to December 2025. To provide insight into this unusual social pairing, a biopsy sample was collected, with genetic analyses pending. Overall, while multiple sightings within short intervals may reflect brief periods of near-island use before individuals or groups return offshore, Fraser’s dolphins do not appear to regularly inhabit near-island waters in Hawaiʻi. Instead, occasional near-island-presence is likely explained by transient oceanographic conditions, consistent with observations of this species elsewhere.
Citation:
Barrios, D.M., C.J. Cornforth, O.K. Miller, V. Pease, and R.W. Baird. 2026. Rare Near-Island Sightings of Fraser’s Dolphins in Hawai’i, Including a Lone Individual Associating with Pantropical Spotted Dolphins. Presentation at the 26th Biennial Conference on the Biology of Marine Mammals, San Juan, Puerto Rico, 19-23 October 2026.
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