Saturday, October 22, 2011

Strandings provide rare close-up glimpse of the odd ocean sunfish

Strandings provide rare close-up glimpse of the odd ocean sunfish


Photo courtesy of "Krill" Carson

Mass Audubon seasonal researcher Tempe Regan is about to do a post-mortem on this ocean sunfish in Truro on Oct. 5.


By Rich Eldred
Posted Oct 14, 2011 @ 07:29 PM
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The inner arm of Cape Cod Bay is not only bad news for whales. Dolphins and sea turtles – it’s the end of the line for many an ocean sunfish as well.

The ocean sunfish is a large (up to 5,000 pound) flattened orbicular shaped fish with large dorsal and anal fins but virtually no tail fin. The reduced tailfin serves merely as a rudder while the other two fins proved the power. They’re often taller (up to 14 feet) than they are long (up to 10 feet). They’ll float near the surface, perhaps sunning themselves, with their large dorsal fin breaking the surface.

The Mola mola (its memorable scientific name) sports a beak-like mouth used for chewing up jellyfish and other similar gelatinous creatures.
Since there are a lot of jellyfish adrift in New England waters they aren’t uncommon offshore but few people have ever seen one alive.

One person who has seen a lot of sunfish is Carol “Krill” Carson, of Middleboro who founded the volunteer New England Coastal Wildlife Alliance in 2005. Her New England Basking Shark Project is dedicated to collecting sighting and stranding information on both basking sharks and ocean sunfish.

“That’s another large fish nobody knows anything about,” Carson said. “I thought wouldn’t it be nice if we could create a sighting network. The more eyes we have the more we can learn.”

The slow swimming sunfish arrive from the tropics in mid-summer and begin washing ashore right about now.

“They start (stranding) around late August and continue till early December, with September/October/November the highlight,” she reported. “They come in before the torpedo rays and sea turtles. We see them offshore feeding on jellyfish and for some reason they start to strand this time of year.”

They don’t seem cold-stunned like the sea turtles nor are they ill like dolphins. Perhaps they are feeding too close to shore. Carson often suggests people re-route them back out to sea.

“They get themselves in a bad position and the tide goes out,” she said. “When they’re high and dry they’re impossible to move. But in even a couple of inches of water you can move them easily. They are like saucers.”

The fish that wash up on Cape Cod Bay are smaller than those 2-ton giants. Carson suspects they are juveniles, much like the sea turtles that strand.

“Two weeks ago a couple called from Indian Neck [in Wellfleet]. I live in Middleboro and they said an ocean sunfish was stranding. I asked ‘Is it high tide yet?’ And told them ‘If it is safe you just push it back in,’ and they did,” Carson recalled. “They saved it because they caught it before it stranded.”

One sunfish discovered in Truro Oct. 5, wasn’t as lucky. The people who reported it to Wellfleet Bay Wildlife Sanctuary thought it was a dead sea turtle. Carson arrived the do a necropsy and collect data. Another one turned up in Sandwich over the weekend. Carson has recorded eight so far this year. Last year she was able to rescue two and necropsied 18.

“I think a lot are funneled into the bay side of the Cape,” Carson said. “They should be moving south like everything. They’re more tropical fish.”

It isn’t that easy collecting data, weighing the fish is a problem.

“I’ve learned how to measure them, photographed them, sexed them, and I’m collecting tissue samples in my freezer at home. I was contacted by a researcher in England who wanted samples so he could compare DNA so I sent him 26 samples,” Carson said. “David Clapp and Sam McGee are helping by creating a portable tri-pod with a crane scale to get weight measurements. It’s sort of a fun project. It’s true science.”

One thing surprised Carson. While sunfish are classified as the heaviest boney fish in the sea she can cut through any part of the animal. Including the skull, with a basic knife.

“They’re more cartilaginous than anything else,” she noted.

She’s learned to age them by counting the rings in the vertebrae.
Anyone who encounters an ocean sunfish on the beach, dead or alive, is urged to call Carson.

“I did two ocean sunfish yesterday and because they were sitting on the beach so long everything was decomposed,” she said. “The faster I get to the beach the better it is.”

Read more: Strandings provide rare close-up glimpse of the odd ocean sunfish - - The Cape Codder