Spinner dolphins are one of the most delightful sights along the Hawaiian islands. These small, highly social marine mammals are known for their fun flips and tricks along the islands’ rugged coastlines.
These playful dolphins draw thousands of tourists to the water to watch their acrobatic antics.
Sadly, the increased attention of tourists may be harming spinner dolphins. The uptick in snorkeling and sightseeing boats over the past four decades could be affecting the pods’ ability to reproduce.
Dolphin calves under 2 years old make up just 9% of the population off Hawai‘i Island. That’s only about half of what is needed to sustain a healthy, stable population, according to a study published this month in Endangered Species Research.
“Our recent findings are rather depressing. Dolphins are not producing enough calves for the population to stay stable—and it’s likely due to human pressures,” Lars Bejder, director of the Marine Mammal Research Program at University of Hawai‘i Mānoa (UH), told me in an email.
If Dolphins Disappear, Hawaiian Tourism May Take A Hit
In Hawaiian culture, spinner dolphins are called Naiʻa. They are considered guardians or protectors that watch over and help people, especially those traveling on the ocean, according to the Maui Ocean Center.
If dolphin populations decline, it spells bad news for local communities. It could negatively impact the marine ecosystem, as well as the economy. Dolphin tourism generates more than $100 million annually for the state’s economy, with each dolphin valued at $3.3 million over its lifetime.
Spinner dolphins return to shallow bays each morning after hunting at night, resting in large pods in calm waters. This predictable behavior makes them popular tourist attractions.
But tourists may be loving the little spinner dolphins to death.
“The evidence suggests chronic human disturbance—especially tourism and recreational-related interactions during critical dolphin resting periods—as a likely contributing factor affecting reproductive success and calf survival,” said Fabien Vivier, the researcher from UH who led the study, in a press release.
Vivier and his colleagues conducted drone surveys of free-swimming spinner dolphins to estimate body size and age structure of pods off Hawai‘i Island as part of his doctoral research at the UH Mānoa School of Ocean and Earth Science and Technology.
They found fewer calves than expected, which doesn’t bode well for the longevity of this isolated population.
Previous research from the UH Marine Mammal Research Program helped inform a 2021 federal rule requiring people and boats to remain at least 50 yards away from spinner dolphins.
But the latest research suggests this distance is not enough. Humans are still disturbing dolphins while they rest, which seems to impact the pods’ overall health —much like our health would suffer if we had a constant stream of tourists tromping through our bedroom each night.
“Historically, it has been very difficult to quantify the effects of human disturbance to whales and dolphins. Sure, we can show that animals change their behavior and perhaps move away. But quantifying the consequences of these altered behavioral changes is difficult,” Bejder told me.
The new study is powerful, Bejder said, because it shows “the cumulative effects of years of chronic exposure to seemingly benign human activities”: the dolphins are not able to produce enough calves to sustain the population.
Bejder believes that additional regulations are needed to help spinner dolphins thrive in Hawai‘i. For instance, time-area closures in certain bays could keep people out of critical habitat for a few hours each day, giving pods the chance to rest peacefully.
This research can inform management options that balance tourism and cultural stewardship with marine mammal protections. Hopefully, we can keep Hawaiʻi’s spinner dolphins leaping long into the future.