A juvenile basking shark that washed up in the surf on Menemsha Beach Sunday likely died of cold shock, according to biologists.
The young shark, a female, drew onlookers to the beach Sunday to take pictures and get a rare close glimpse at the animal. On Tuesday, scientists arrived to perform a necropsy and gather information that will contribute to shark research as a whole.
“It’s very unusual to have this shark here this time of year,” senior state shark biologist Gregory Skomal told the Gazette by telephone Wednesday morning.
Mr. Skomal said there were no obvious signs of a cause of death. “My guess, and probably anyone’s guess, is that it died of cold shock,” he said “It’s the time of year that basking sharks are not in this area, they move out of here and migrate to warmer areas.
“Water temperatures are very cold and probably the animal was lost,” he continued. “We don’t know why it didn’t migrate out.”
The shark was a juvenile, Mr. Skomal said, though the age is uncertain because basking sharks are “a species we have very little information on in terms of longevity and growth rates and size and age.” The shark was about 15 feet long.
Basking sharks usually arrive in New England waters in mid to late May and head south as early as August and as late as the end of November. Most leave by late September.
The sharks feed on tiny crustaceans called copepods, shrimp-like zooplankton. The sharks “rely heavily on the balloons of copepods that emerge here in spring, summer and fall . . . food availability isn’t as high in the winter,” Mr. Skomal said. “That’s why talking about basking sharks here in January, there’s probably a problem.”
The shark was thin and appeared to be emaciated. “The stomach by all accounts was largely empty,” Mr. Skomal said. “It may not have been feeding, it may not have been finding adult plankton patches and probably could not tolerate the extreme cold.”
While the shark had what appeared to be fishing line around its snout, Mr. Skomal said that was not a cause of death. “No, these animals are a lot stronger than that,” he said, noting that the fishing line was gone by the time scientists arrived. “Nothing that would have compromised the animal’s survival.”
Division of Marine Fisheries biologist John Chisholm, intern Grace Casselberry and Matt Pezzullo with National Marine Fisheries Service visited the Island Tuesday to perform a necropsy.
“There’s a lot you can learn from a dead animal,” Mr. Skomal said, and dead sharks offer information that is otherwise difficult to acquire.
“We don’t really want to go out and harpoon and kill basking sharks to learn more about them,” he said.
In marine mammals, he said, the cause of death seems to be the most important question to answer. With sharks, information focuses on the shark’s life.
Tissue samples answer questions about life history, and the shark’s stomach contents show what the animal has been eating. A dissection allows a look at the reproductive system to answer questions about age and growth.
Mr. Chisholm took the snout of the shark to study parasites that live in shark noses. The liver will be weighed and compared to healthy shark livers.
Mr. Skomal said one or two sharks a year, mostly basking sharks, wash ashore in the southern New England area. This is the third basking shark Mr. Skomal recalls washing up on Martha’s Vineyard, with others showing up at Philbin Beach and near Dogfish Bar. These included a 30-foot-long adult male. “It’s not very unusual to have them there,” he said. “It’s part of their migratory movements.” For this shark, “the time of year is the unusual part.”
“You learn a little bit about each shark, but really what you do is you combine it with data from multiple sharks,” Mr. Skomal said. Over the years, “a picture emerges as you plot this shark out with the rest of the group.”
Chilmark resident Jeremy Mayhew was out for a walk with his daughters when they saw the shark wash ashore around 12:30 p.m. Sunday.
“I saw those fins start rolling around out a little distance, they just kept coming in closer,” Mr. Mayhew told the Gazette. He said the shark was still alive when it beached. “It was flopping around, kind of struggling,” he said, and opening its mouth.
Mr. Mayhew contacted the Woods Hole Oceanographic Institution to let them know about his discovery.
“I recognized it as a basking shark . . . and I was pretty amazed just to see it,” he said. “I knew they weren’t supposed to be in the waters at this time.”
He said he saw a basking shark that washed up on Philbin in the past, and has seen them in the wild. “I have seen them before, out swordfishing with my father . . . it’s really quite amazing to see them going by with their mouths wide open. They’re beautiful creatures,” Mr. Mayhew said.
His twin daughters, nearly two years old, “didn’t know what to make of it,” Mr. Mayhew said, though they did start saying “shark.”