Kaua‘i fisherman finds oddity in belly of tuna; scientists identify rare octopus

Marine biologists on Kaua‘i have finally resolved a pint-sized yet long-standing enigma emerging from the depths of the Pacific Ocean.

Local fisherman and chef Alan Okuhara uncovered the tiny mystery several years ago while cleaning an ahi, or Pacific yellowfin tuna.

“Ahi fishermen, they cut up the ahi belly for see what they feeding on, for the color of your skirts and everything else, so you can know what lures you can run,” said Okuhara, who co-owns the popular restaurant Mark’s Place in Puhi. “It just so happened I found an octopus in the belly … I thought it was a squid, but the head was totally different.

“It was like a cross between a squid and an octopus, so I wasn’t sure what it was,” Okuhara continued. “It was the first time I’d seen one like that, so I gave it to Molly.”

Molly Lutcavage, a marine biologist and longtime researcher of Atlantic bluefin tuna, has studied ahi in Hawai‘i since 2015. She is a staunch advocate of partnerships between researchers and fishermen; in February, she organized a series of meetings between Kaua‘i fishermen and Capt. Dave Marciano of the National Geographic Channel’s long-running reality television series “Wicked Tuna.” Marciano, who has partnered with Lutcavage in the past, touted the benefits of scientific collaboration while swapping fishing yarns with his Garden Isle counterparts.

Lutcavage was intrigued by her friend Okuhara’s tentacular discovery. She too was unable to identify the small creature.

“This is an Alan thing,” Lutcavage laughed, explaining Okuhara habitually poses questions that baffle her scientific expertise.

Invoking the classic NPR program “Car Talk,” she continued: “You know ‘Stump the Chump’ with Click and Clack, the Tappet Brothers? … I’m the chump, and we try not to be stumped.”

Lutcavage placed the unknown cephalopod in a 30-milliliter vial filled with formalin, a standard preservative containing formaldehyde, and began searching for someone able to provide answers. She eventually delivered the specimen to Heather Ylitalo-Ward, the Hawai‘i Department of Land and Natural Resources Division of Aquatic Resources’ Kaua‘i district biologist. Ylitalo-Ward studied sexual selection in he‘e pali, or rock tako (Octopus oliveri) while pursuing her doctorate at the University of Hawai‘i at Mānoa.

“It fell down my list and I forgot about it,” she admitted. Ylitalo-Ward manages a small team responsible for all manner of duties, ranging from environmental education to removal of non-native coral from local reefs. “Then, the other night at the small-boat fisher meeting, Alan was there and said, ‘Remember the octopus that I gave you?'”

Ylitalo-Ward uncovered the specimen still floating in its vial. Looking closely, she noted the animal measured three centimeters long, had very large eyes, a very small head and a set of tentacles longer than their mates – an unusual trait for an octopus.

“In squid, obviously, they have two longer feeding tentacles that we’re familiar with,” she said. “Octopuses generally have pretty similar arm length all the way around, but this one clearly had very different size arms. I was thinking, ‘What could this possibly be?'”

Ylitalo-Ward finally settled on a visual identification, determining the specimen to be a male blanket octopus – a genus of rarely-seen octopus inhabiting the open ocean, or pelagic zone.

Blanket octopuses, which comprise four species found in waters throughout the world, lay claim to a variety of interesting features: Their name is derived from the long webs or capes connecting adult females’ arms. Males and immature females are known to rip tentacles from venomous Portuguese man o’ war (siphonophores closely related to jellyfish) for their own purposes.

“They’re able to collect some of those stinging tendrils, connect them to their arms and use them as a bit of a defense mechanism against being eaten by predators,” said Ylitalo-Ward.

The blanket octopus also boasts extreme sexual size-dimorphism and has one of the greatest sex size discrepancies in the animal kingdom. Female blanket octopuses reach six feet in length and weigh 40,000 times more than their diminutive male counterparts, which average less than three centimeters in length.

“They’re like aliens … the females are beautiful,” exclaimed Lutcavage. “But the tiny males, biting off pieces of Physalia, or man o’ war, and using them for defense: It’s just crazy. I’d like to see that in action.”

Ahi hunt in schools, chowing down on whatever is available – mostly small fish and squid. However, one fish destined to land on the Mark’s Place menu swallowed a blanket octopus whole, sparking an inquiry into the vast wonders of the ocean.

Okuhara is delighted to have, at long last, a solution to the puzzle he uncovered years ago.

“It’s really interesting,” he said.

But Okuhara – who Lutcavage describes as a scientist in his own right – still has questions that stump his friend and colleague.

“Alan brought me another mystery that we’re still trying to solve: In ahi, there’s a structure that people like to eat,” Lutcavage said. “But nobody knows what it is or what it does … It doesn’t occur in any other tuna, like bluefin or bigeye.”

The structure is found in the stomach cavity of ahi and is made out of collagen and elastic fibers with almost no blood supply. It’s well-known to Hawai‘i fishermen, many of whom eat it, comparing its chewy texture to abalone.

“I’ve asked everybody … Nobody knows what it does. They just say, ‘Oh, it’s chewy and people eat it,'” said Lutcavage. “But listen: Form and function. Nature doesn’t just do things for no reason. I know it has a function of some kind or it wouldn’t be there.”