Pods of playful Hawaiian spinner dolphins are popular with tourists along the western shore of Hawaii’s Big Island. But noise from sightseeing boats and other coastal users wakes these vulnerable animals from their essential daytime slumber, a new study shows. A pending federal rule would protect the species, but advocates on both sides are unhappy with it.
Like all dolphins and whales, Hawaiian spinner dolphins (Stenella longirostris) rely on sound to communicate and forage. They hunt in the coastal ocean at night, when shrimp and squid—their favorite foods—migrate upward from deeper waters. The dolphins work together to herd hovering prey into clumps, and each individual feeds in turn. Full and fatigued, they retreat to sheltered “resting bays” along the heavily trafficked Kona coast, where they normally snooze and quietly schmooze during the day.
To document the impacts of boat engines, military sonar, and other unnatural sounds on these animals, a team led by biologist Heather Heenehan of the Duke University Marine Laboratory in Beaufort, North Carolina, deployed underwater acoustic recorders in four popular resting bays off the shores of Kona, Hawaii, from 2011 to 2013. Terabytes of recordings showed that under natural circumstances, the bays were loudest at night with sounds of snapping shrimp and clicking dolphins on their group hunts. But during the day, whale watch boats, snorkeling charters, and naval ships produced volumes of sound up to 45 decibels higher than the natural nautical noises. Forced awake, the dolphins began to vigorously click with one another in an effort to communicate over the din, the team will report next month in Marine Policy.
This humanmade noise takes a toll, says study co-author Julian Tyne of the Murdoch University Cetacean Research Unit in Perth, Australia. Tour boats alone generate enough noise to disturb daily dolphin siestas, forcing the animals to pull the daytime equivalent of “a few ‘all-nighters’ in a row,” he says. “The dolphins are exposed to these human activities over 80% of the time, when they should be resting.”
Under the Marine Mammal Protection Act of 1972, the barrage of sound may constitute illegal harassment, the researchers believe. The dolphins can’t just go elsewhere to avoid the cacophony, they note, because they use the secluded bays to avoid sharks. Moreover, surveys suggest the Kona coast population of spinner dolphins has declined from 2300 in the 1990s to about 600 today, based on the team’s focal surveys. The team has yet to study the effect of sleep deprivation on the dolphins’ well-being, but they believe noises are from fully awake dolphins. But spinner dolphins are exposed to human activity more often than any other cetacean in the world, the researchers say, and the humanmade noise probably isn’t helping.
The National Oceanic and Atmospheric Administration (NOAA) issued a proposed rule in August to prohibit tourists from swimming with the dolphins or boats to come within 45 meters of them. But the regulations—extended for public comment through today—are controversial.
A 45-meter buffer isn’t enough, says Peter Thomas, international and policy program director at the Marine Mammal Commission in Bethesda, Maryland, who was not involved in the study. That margin still leaves the species vulnerable to human disturbance and noise, he says. Thomas calls for complete time-area closures, which would prohibit human activities during peak spinner dolphin resting periods in the most critical bays—a position supported by Heenehan’s team.
But time-area closures are too intrusive for the Big Island’s visitors, says Jim Coon, president of Hawaii’s Ocean Tourism Association in Maui. Coon is concerned that public comment on NOAA’s proposed rule allows those who are less familiar with the situation, like people who don’t live in Hawaii, to carry the same weight as locals, who, he says, are generally the best informed and the most affected. “It’s important … that the local community is educated and part of the decision-making process.”
No single solution will satisfy everyone, says sustainable tourism expert James Higham of the University of Otago in New Zealand, who was not part of the study. Although robust populations of dolphins can handle whale watching and other human influences, more tenuous groups might not make it, he says. Further studies should determine the size, health, and level of isolation of specific Hawaiian spinner dolphin populations to discern which ones need strict rules against human contact, Higham urges: “Priority No. 1 should be to protect them and to safeguard them from imminent risk of extinction.”