There are plenty of aquatic predators near the shore to worry about, but channel swimmers are concerned about another dangerous fish in the open ocean: cookiecutter sharks.
In the past decade, a handful of swimmers have been bitten while attempting to cross the Ka’iwi Channel between Oʻahu and Molokaʻi.
In some instances, multiple sharks attacked a single swimmer, carving out round pieces of flesh from their victim and leaving cookie cutter-shaped bite marks.
Michael Spalding survived an attack in 2009 while crossing the ʻAlenuihāhā Channel from Hawaiʻi Island to Maui, suffering a bite to his calf and stomach.
That day, he started at 3 p.m. when he believed the tide to be perfect. About 10 miles into the swim and five hours later, Spalding said he felt the first, shallow bite on his chest.
"It was just like a pinprick but it alerted me the fact that I have to get out of the water as quick as possible," he told reporters after the incident.
A recent study from University of Hawaiʻi researcher Steven Minaglia, a channel swimmer himself, found a striking association between cookiecutter shark bites and moonless nights.
After years of observing shark bites, Minaglia said he noticed that five of the six victims were bitten when the moon was absent from the sky. He added that they were bitten in almost the same location within the channel, swimming over very deep water.
"The only way to prove a theory that dark is a risk factor was I had to look at the people swimming in the light and find out what was unique about them. And that's when the project really took off," he said.
He said he spoke to hundreds of swimmers and even some doctors who could give context to his theory.
Going forward, he said he will keep a close eye on swimmers for recurring patterns in the data.
"I look at it as maybe it's a lifetime of research into this. I don't think we're finished with it."
To read the report, click here.
This story aired on The Conversation on March 7, 2024. The Conversation airs weekdays at 11 a.m. on HPR-1.
