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Marine biologists near end of 5-year study on health of Hanauma Bay

hanauma bay oahu Hanauma Bay Nature Preserve
Sophia McCullough
FILE - Hanauma Bay Nature Preserve. (April 12, 2022)

The University of Hawai‘i Institute for Marine Biology is winding up a five-year visitor capacity study on Hanauma Bay on Oʻahu.

Researchers are comparing data from before, during and after the ninth-month closure from March to December 2020 during the pandemic.

"We were really lucky because when they reopened the bay, they opened at 25% capacity of what it had been in 2019 numbers. And then they gradually increased to 50% capacity," said Ku’ulei Rodgers from the Coral Reef Ecology Lab. "So we were able to see what the differences were."

She said there were fewer fish as the number of people increased, but the biggest difference was the water quality.

"We put sediment traps in to see how much sediment is deposited on the bottom and then took water clarity measurements. The bay was 56% clearer during the COVID-19 closures than before the closures when it was open to the public in 2019," Rodgers said. "And then after the reopening of the bay, water clarity decreased again by nearly 30%."

Upon reopening after the pandemic, Hanauma Bay decided to remain closed twice a week on Monday and Tuesday — up from just one day.

Also after the pandemic, the bay implemented a reservation system and increased the nonresident visitor fee to $25.

"We recommend that they incorporate biological, physical and social aspects when they're looking at sustainability approaches. Besides the social carrying capacity, we're also doing a physical carrying capacity right now," Rodgers said.

Rodgers said one of the most disturbing findings was the predicted result of sea level rise. Based on models from NOAA and UH, a 6-inch sea level rise is predicted to occur by 2030, which would decrease the usable beach area at Hanauma Bay by 88%.

This interview aired on The Conversation on Jan. 30, 2023. The Conversation airs weekdays at 11 a.m. on HPR-1.

Catherine Cruz is the host of The Conversation. Originally from Guam, she spent more than 30 years at KITV, covering beats from government to education. Contact her at ccruz@hawaiipublicradio.org.
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