A basking shark that was found washed up dead Wednesday in Blue Hill was not fully grown, but its cause of death is not yet known.
Researchers who conducted a necropsy on the male shark on Thursday did not come away with an explanation for why it died.
“There’s no obvious sign of cause of death,” John Chisholm, a shark scientist with the Boston-based New England Aquarium, said Friday. “A lot of times we can’t really figure out why.”
Chisholm, who drove from Massachusetts to examine the shark carcass, said he took tissue samples to see if the shark may have been sick, but has to wait on test results to find out. He was assisted on the necropsy by researchers from the Maine Department of Marine Resources and College of the Atlantic in Bar Harbor.
“That pathology will take a while,” he said.
The shark was measured at 24 feet long, but fully grown basking sharks can reach lengths of 35 feet or more, Chisholm said. Basking sharks, so named because of their habit of swimming slowly along the ocean’s surface, grow to sizes exceeded only by whale sharks, which are the largest type of fish on the planet.
Chisholm said he is trying to determine if the dead shark is the same animal that was recorded on video earlier in the week close to shore at Swan’s Island and then later in Blue Hill. He said he heard someone may have struck the shark with a boat in Blue Hill while trying to get a close look, but that the shark seen at Swan’s Island already seemed to be acting strangely.
“It probably is the same shark,” Chisholm said of the dead shark and the one shown in the recordings. “Sometimes they just have bad luck.”
Basking sharks have been known to get stuck in shallow waters as the tide goes out while they are feeding, he said. Marine mammals such as porpoises, dolphins or whales sometimes can be rescued from strandings because they breath air and can survive getting stuck on the shore, but such strandings are fatal for sharks, which require water to breathe.
Basking sharks resemble white sharks, which frequent Maine waters in the summer to feed on seals and fish, but that resemblance disappears when they feed, Chisholm said. Basking sharks have no teeth and swim with their huge mouths agape as they filter food such as plankton, krill and small fish from the water.
This is a big year for basking sharks in the Gulf of Maine, Chisholm said, and he’s been getting a lot of calls from people this summer who mistake them for white sharks. Basking shark accumulations in the gulf are cyclical, he said, and this is an above average year.
“People want to see white sharks, but this is a huge year for basking sharks,” he said. Basking sharks are more commonly sighted because they tend to be at the surface more than white sharks.
Basking sharks tend to leave people alone because they feed on much smaller prey. But Chisholm said that even though white sharks are spotted less often, it doesn’t mean that they’re not around. White sharks feed on seals, porpoises and large fish, all of which are common in the Gulf of Maine.
“If you are in the water in Maine, you have to be aware you’re in white shark habitat,” Chisholm said, adding that people should avoid getting in the water near seals or schools of fish.
“Don’t swim with the bait,” he said.
As for the shark carcass in Blue Hill, Chisholm said nature will take its course. Shark skeletons are made out of cartilage, not bone, so they tend to decompose more fully than a whale skeleton.
He and other scientists cut apart the dead shark during the necropsy, and the tide and other marine creatures will do the rest, he said.
“It will be a real windfall for all the local crabs and other scavengers,” he said.
