Researchers at the Hawaiʻi Institute of Marine Biology report that spinner dolphin populations along the Kona Coast are slipping, and human disturbance is a likely driver. Using 3D body measurements from drone images collected in 2021 and 2022, scientists estimated age classes and found calves made up only 9% of the population, compared with about 17% expected for a stable group.
HIMB’s Marine Mammal Research Program director Lars Bejder called the findings a wake-up call, noting years of concern from federal officials, community members, Hawaiian practitioners and some commercial operators about mounting pressure on these animals. Spinner dolphins typically live 20 to 25 years and reproduce slowly, so a drop in calves is expected to cascade into fewer adults over time.
The team said the results add important new evidence and raise concerns about the long-term viability of the Big Island population, while underscoring the need for stronger protections and better enforcement.
Spinner dolphin populations Need Rest
Spinner dolphin populations rest during the day in sheltered bays after feeding offshore at night. In Kona, steady tour activity and in-water recreation often interrupt that rest.
A 2018 UH study found dolphins were exposed to people within 100 meters for an average of 83% of their daylight resting time, and other research linked that disturbance to behavior changes and reduced rest. Bejder said he is unaware of another dolphin population that experiences such high levels of contact with people.
In 2021, the National Oceanic and Atmospheric Administration adopted a 50-yard approach limit for people and vessels under the Marine Mammal Protection Act. The rule spans a vast area, and while NOAA has partnered with the U.S. Coast Guard and the state Department of Land and Natural Resources Division of Conservation and Resources Enforcement to uphold it, the benefits for dolphin rest are unclear.
By 2024, the agency had issued about 135 tickets and 76 penalties, ranging from 100 to 4,500 dollars.
DLNR spokesperson Andrew Laurence said spinner dolphin violations can be reported to the state, but officers can only respond, investigate and refer cases to NOAA’s Office of Law Enforcement. DOCARE now conducts marine patrols on Oʻahu, Hawaiʻi island, Maui and Kauaʻi, and NOAA Fisheries reports 614 patrols across the Pacific Islands region between 2021 and 2024.
Concerns also extend to tour operations off West Oʻahu, where roadside crowds have gathered in recent years to swim with resting dolphins. In 2021, one tour operator was fined 2,500 dollars for harassing dolphins by circling a pod and dropping swimmers among them.
In 2023, 33 swimmers were accused of harassing dolphins off Hawaiʻi island.
Are Closures Necessary?
Beyond the 50-yard rule, HIMB researchers urged NOAA to revisit a second measure first floated in 2021. The proposal would create daily time-area closures from 6 a.m. to 3 p.m. at four Hawaiʻi island sites, Kealakekua Bay, Hōnaunau Bay, Kauhakō Bay (Hoʻokena) and Makako Bay, and at La Perouse Bay on Maui, to protect resting dolphins.
The idea drew extensive public comment at the time, with more than 700 submissions both supporting and opposing the plan. NOAA documented 47 spiritual retreats and 47 commercial tour operators offering close, in-water dolphin encounters on Hawaiʻi island in 2017.
Critics argued dolphins sometimes approach people, and said evidence of harm from human activity was lacking. The Hawaiʻi Fishing and Boating Association and Jack’s Diving Locker opposed the rule.
The Hawaii Dolphin Educators’ Association said stronger enforcement of existing law would suffice. The Marine Mammal Commission supported closures and recommended buffer zones to keep vessels from positioning just outside the boundary near resting dolphins.
The commission also urged outreach to clarify that most other ocean recreation, including spearfishing and freediving, would remain largely unaffected. The Kauhakō ʻOhana Association submitted signatures supporting the proposal, and several commenters noted allowances for Native Hawaiian practitioners to continue customary practices.
Others, including Native Hawaiian scientist Roxane Keliʻikipikāneokolohaka, called the approach heavy-handed. NOAA has not finalized the closures.
Stefanie Gutierrez, a spokesperson for NOAA Fisheries’ Pacific Islands Regional Office, said spinner dolphins depend on shallow, nearshore bays by day to rest, socialize and care for young, and that disruptions during these hours can affect long-term survival. She said the time-area closure rule remains under deliberation, without a timetable.
From the tour industry side, Fair Wind Cruises president Mendy Dant said she has observed more calves since the 50-yard rule began, though she has seen limited DOCARE enforcement since 2021. She said proposed closures would not affect the company, which already avoids the center of Kealakekua Bay to leave space for resting dolphins.
Dant added that many operators comply by stopping short and letting wind drift carry them, and that dolphins sometimes approach boats. She expressed more concern about unguided kayak users who may not know the rules.
Bejder emphasized that the problem is broader than tourism alone. Any recreation that intrudes on resting areas can add to cumulative stress.
He said marine tourism is valuable, but it must be done sustainably to protect both the dolphins and the industry that depends on them.
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