Researchers took advantage of the pandemic to see how thousands of snorkelers can change an ecosystem.

A new study that examined years of data on the presence of fish in Molokini Crater before, during and after the pandemic has found that the daily barrage of tour boats and snorkelers drastically changes the way fish use the marine ecosystem. 

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Before the pandemic paused tourism in Hawaii, the number of tourists flocking to Maui was reaching all-time highs. More than 40,000 tourists came in August 2019 to snorkel or dive in Molokini, a crescent-shaped islet off the southwestern coast of Maui.

By the next spring, Hawaii locked down to stop the spread of Covid-19, and for the first time in recent history, there were no visitors to Molokini.

For researchers like Kevin Weng of the Virginia Institute of Marine Science, it was an unheard-of opportunity to study the way that human activity changes the marine environment in one of the busiest snorkeling destinations in Hawaii.

“Our conclusions from this study are that we should reduce the human footprint at Molokini,” Weng told Civil Beat. 

The crescent-shaped Molokini islet is a popular snorkeling and diving excursion off of Maui. (Nathan Eagle/Civil Beat/2020)

The study released Wednesday in the scientific journal PLOS was conducted in partnership with the National Geographic Society’s Alan Friedlander and Whitney Goodell and the Hawaii Department of Land and Natural Resources’ Laura Gajdzik and Russell Sparks.

During the height of the pandemic, the researchers teamed up to send divers to Molokini to document the volume and types of fish in the area, building on similar surveys that had been regularly conducted years before anyone had heard of Covid-19. The scientists also captured fish and put tracking devices on them to shed light on how they moved in and around Molokini during the day and night. 

The findings were clear. Since 2004, the volume of fish at Molokini had dropped, even though fishing hasn’t been allowed in the protected area for decades. But when the pandemic lockdown hit and tourists and snorkel boats disappeared, the fish population suddenly rebounded.

This chart shows monthly changes in the number of people visiting Molokini since 2013. (Courtesy: PLOS/2023)

The biomass of fish — the measurement used to estimate how many pounds of fish are living per square meter or acre — surged. Scientists also documented more predators, like omilu, in the shallow waters protected by the Molokini Crater. 

When the tourists returned, things changed again. Researchers were able to document that when Molokini was packed with boats and people — usually in the mornings when the wind is calmer — the predators left to deeper waters, something they didn’t do when the area was free of people. The volume of fish dropped again to pre-pandemic levels. 

The scientists are still working to understand what that means for the health of the delicate ecosystem and how it might influence marine life ranging from corals and smaller fish to the predators themselves. 

“It’s a major undertaking to do all this,” said Weng. “Normally, you would want to have a grant with lots of funding in order to undertake a project like that.” 

For years, scientists have been studying the presence of fish at Molokini Crater. (Courtesy: Kevin Weng)

Because of the pandemic’s unexpected arrival, Weng and his colleagues didn’t have the typical time to plan or apply for grants to pay for the study. Instead, they connected with the nonprofit Maui Nui Marine Resource Council, which helped them raise more than $4,000 for the project. The nonprofit also linked them with Maui residents who were willing to loan out their cars and temporarily house the scientists. 

The effort came as a growing number of Maui residents are calling for state leaders to reform the community’s reliance on tourism.

The study calls for examining ways to reduce the traffic in Molokini by focusing on attracting a smaller number of tourists who are willing to spend more money, rather than making things cheap to attract as many paying customers as possible. 

“Molokini is being over-used,” DLNR’s Russel Sparks said in a news release. “Management is needed to improve not only ecosystem health but the visitor experience.”

Civil Beat’s coverage of Maui County is supported in part by grants from the Nuestro Futuro Foundation and the Fred Baldwin Memorial Foundation.

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