Fishing gear threatens Hawaii's already endangered false killer whales

A concerningly high number of endangered false killer whales are being injured when they get hooked by fishing gear in waters off the main Hawaiian islands, according to a new research paper released Thursday.

Published in the scientific journal Endangered Species Research, the research concludes there should be closer monitoring of that unique but dwindling local population and how the creatures — actually dolphins, not whales, and not killers — interact with the small-scale commercial and recreational boats that fish in those waters.

That could include installing cameras to record encounters with the false killer whales, which feed on the same large fish those boats catch and often go after what is already on the hook, said Robin Baird, a research biologist with the nonprofit Cascadia Research Collective, which led the study.

Injuries such as this to a false killer whaleʻs dorsal fin typically happen as the dolphin struggles to free itself from fishing gear. The fin often gets damaged against the taut fishing line. (Courtesy: Robin Baird/Cascadia Research)

“We have an idea of where these interactions are likely occurring, but we donʻt know when theyʻre occurring or with what type of gear,” Baird said Wednesday. “Being able to come up with solutions requires (this) information.”

Cascadia, along with two Hawaii-based wildlife foundations and federal fisheries officials, analyzed photographs taken between 1999 and 2021 of three false killer whale populations found near or around the Hawaii archipelago, including the endangered group that inhabits the waters off the main islands.

The researchers flagged the photos that showed clear fishing-related injuries to the animalsʻ mouths and dorsal fins. The endangered group had the most documented injuries by far, the study showed.

Researchers were able to find photos of both the dorsal fin and the mouth for 153 individual dolphins for that group. Out of those 153, some 44 dolphins had been injured by fishing gear, the study found — nearly one in every three.

False killer whales hunt the same large species of fish coveted by local fishers in Hawaii, including ahi and mahimahi.

The rate of injury was drastically lower for the other two Hawaii populations, which arenʻt endangered. One of them is a pelagic, roaming group of several thousand dolphins. The other, which inhabits the Northwestern Hawaiian Islands, has nearly 500 individuals, according to the study.

The endangered group near the main islands is down to an estimated 138 dolphins, according to the study. Itʻs the only endangered population of false killer whales in the world, according to Baird. Theyʻre found anywhere from just off the beach to tens of miles offshore.

That swath of ocean generally coincides with Hawaiiʻs federally mandated “exclusion zone” — a region up to 70 miles offshore where the local longliner fleet is prohibited from fishing.

Thus, the dolphins are getting hooked by smaller-scale boats that fish closer to the islands, not the longliners, Baird said.

Thereʻs already a federally organized False Killer Whale Take Reduction Team thatʻs been working since 2010 to try and reduce the number of species deaths, but the fishers represented in that group are all from Hawaiiʻs longline fishing industry.

Baird on Wednesday recommended forming a new, similar hui (group) that would include the nearshore fisherman to address the plight of the endangered false killer whales.

False killer whales typically hunt and feed on ahi, mahimahi and other fish often sought by human fishers in nearby ocean waters. There have even been unique, documented instances in which the marine mammals have attempted to share their catch with people they encounter in the water, according to Baird.