Entanglement in marine debris is a risk for cetaceans worldwide, with 97% of cases caused by derelict fishing gear. Most reports of entanglement cases are of coastal dolphins or baleen whales, and documentation and reporting vary by region. Around the main Hawaiian Islands (MHI), the degree of entanglement risk is difficult to assess as strong currents, remote rugged coastlines, and the presence of scavengers make the discovery and examination of stranded cetaceans unlikely. Here we report observations of two life-threatening entanglements and use a combination of photographs, drone footage, underwater video, and morphometric measurements to assess the severity of entanglements and the types and sources of the marine debris. On 5-May-2021, a juvenile Blainville’s beaked whale (HIMd306), was observed swimming with knotted 4-inch mesh polypropylene netting wrapped around the front third of the body, including a wrap around the rostrum, preventing the whale from feeding. HIMd306 was first encountered in February-2019 and was seen on six occasions prior to entanglement. A morphometric comparison between 11-Mar-2021 and 5-May-2021 revealed weight-loss and poor body condition with evidence of starvation (mid-body average girth decrease was 6.4%). On 22-Oct-2025 an adult male false killer whale (HIPc373) from Cluster 4 of the endangered MHI population (seen 16 times between 2009-2025) was encountered with a loop of 3-strand polyblend rope wrapped tightly around the body, cutting through the leading edge of the partially-severed dorsal fin. New and necrotic tissue suggested wound healing, although trauma to the site was ongoing. HIPc373 was in good body condition, possibly due to food provisioning as prey-sharing is commonly seen in this species. Response crews were organized to assist with disentanglements for both individuals but neither was re-sighted. This is the first documentation of likely lethal entanglements in marine debris of both species, highlighting another threat to island-associated populations in Hawai‘i.
Citation:
Douglas, A.B., R.W. Baird, C.J. Cornforth, M.A. Mohler, S.D. Mahaffy, and S.N. Yahn. 2026. Entangled in Hawaiian Waters: First Documentation of a Blainville’s Beaked Whale (Mesoplodon densirostris) and an Endangered False Killer Whale (Pseudorca crassidens) with Life-Threatening Entanglements in Marine Debris. Presentation at the 26th Biennial Conference on the Biology of Marine Mammals, San Juan, Puerto Rice, 19-23 October 2026.
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