A new study has found that spinner dolphins living off Hawaiʻi Island are having far fewer calves than scientists expected.
The discovery has raised serious concerns that this small, isolated dolphin population could slowly decline if the trend continues.
The research was led by scientists from the University of Hawaiʻi at Mānoa and involved experts from several other organizations.
The findings were published in the journal Endangered Species Research.
Spinner dolphins are famous for their playful leaps and spinning jumps. They are also one of Hawaiʻi’s most popular wildlife attractions, drawing thousands of tourists each year.
However, the same tourism that brings people closer to these animals may also be putting their future at risk.
The study found that calves, which are dolphins younger than two years old, make up only about 9% of the local spinner dolphin population.
In a healthy and stable population, scientists would expect calves to make up around 17%. This large difference suggests that not enough young dolphins are surviving or being born to replace older animals.
Researchers believe that frequent human activity may be one of the main reasons. Previous studies have already shown that the spinner dolphins around Hawaiʻi Island experience more disturbance from people than almost any other dolphin population in the world.
During the day, spinner dolphins return to calm, shallow coastal bays to rest and socialize after spending the night hunting for food offshore.
Unfortunately, these same bays are popular with tour boats, snorkelers, swimmers and paddleboarders. Constant human activity may interrupt the dolphins’ rest, increase stress and make it harder for mothers to raise healthy calves.
To better understand the population, the research team used drones to photograph dolphins swimming near the surface. By measuring their body lengths and comparing them with information collected from stranded dolphins, the scientists created the first growth chart for this spinner dolphin population. This allowed them to estimate the ages of individual dolphins and classify them as calves, juveniles or adults.
Knowing the age structure of a population is important because it helps scientists predict whether a species can survive over the long term. A low number of calves is often an early warning sign that the population is not replacing itself fast enough.
Spinner dolphins are important to Hawaiʻi in many ways. They are part of the islands’ natural heritage, play an important role in the marine ecosystem and support a tourism industry worth more than 100 million dollars each year. Earlier research estimated that each individual spinner dolphin contributes more than 3.3 million dollars to the local economy over its lifetime.
Although a federal rule introduced in 2021 requires people and boats to stay at least 50 yards (46 meters) away from spinner dolphins, many experts believe this rule does not provide enough protection.
The researchers are calling for stronger conservation measures, including closing important resting bays to human activities during the daytime. They hope these changes will give the dolphins the quiet environment they need to rest, care for their calves and recover naturally.
Scientists say protecting this unique dolphin population now is far easier than trying to save it after numbers begin to fall. By balancing wildlife conservation with responsible tourism, Hawaiʻi may still be able to protect these remarkable animals for future generations.
