Rare shark spotted off New England coast
Dusky sharks were hunted to near-extinction in the late 20th century.
A species of large-bodied shark that nearly disappeared from Atlantic waters has been seen feeding on seals off the coast of New England, according to marine biologists.
Typically it's great whites that are expected near the Massachusetts coast in the summertime. However, several sightings of what were believed to be great whites attacking seals actually turned out to be the elusive dusky shark, John Chisholm, adjunct scientist at the New England Aquarium’s Anderson Cabot Center for Ocean Life, told ABC News.
Dusky sharks were nearly hunted to extinction in the late 20th century when commercial fisheries in the Gulf and Atlantic ramped up, according to Demian Chapman, senior scientist and director for the Center for Shark Research at the Mote Marine Laboratory & Aquarium in Sarasota, Florida.
Meat and fins of many shark species are highly valued, and they are targeted and taken as bycatch in commercial and recreational fisheries, according to the Florida Museum of Natural History. The demand for fins came primarily from China, Chapman told ABC News.
As a result, populations of dusky sharks declined significantly. In 2006, populations were estimated to represent between 15% and 20% of their mid-1970s abundance, researchers say.
Shark experts have been recording signs of their comeback in recent years -- bolstered by federal protections issued by the National Marine Fisheries Service, the experts said. In 1993, NOAA Fisheries implemented the first Fishery Management Plan for Sharks of the Atlantic Ocean.
This plan included a prohibition on shark finning -- the process of removing shark fins at sea and discarding the rest of the shark -- and grouping sharks into different complexes to simplify the management of dozens of species. Many of these measures still in place today.
Dusky sharks, along with other species, have been heavily protected since 2000. It was one of the first species targeted for prohibited status under federal regulations, meaning that fisherman who catch them have to release them, Chapman noted.
Their populations are vulnerable and slow to recover because of their slow growth rate, late age of maturation and small litter sizes, Danielle Castillo, zoological curator of aquariums at SeaWorld San Diego, told ABC News.
"These sharks do not reach reproductive maturity until they are around 20 years old and females only reproduce every few years," she said.
They have one of the slowest life trajectories of any shark species, according to the Center for Shark Research's Chapman.
"If they experience high fishing mortality, they just can't replenish the population, so they decline," he said.
Dusky sharks have historically been found off the Massachusetts, Chisholm from the New England Aquarium said. Sightings of them off Woods Hole and Nantucket are mentioned in "A History of the Fishes of Massachusetts," a collection of six installments published between 1853 and 1867 by naturalist David Humphreys Storer, he noted.
"They're starting to recolonize their old stomping grounds, right off of southeastern Massachusetts, off Cape Cod and Nantucket," Chisholm said.
Populations of Dusky sharks have been so low in recent decades that scientists never had proof that they actually fed on seals until recently, Chisholm said.
In 2020, researchers began receiving reports by citizen scientists of grey seals being preyed on by sharks. The assumption was that species were white sharks, since they also prey on seals in the region, Chisholm said.
The mistake may have to do with their similar colors and sizes, at times, the experts said. Males dusky sharks can grow up to 14 feet, which is about the size of a sub-adult white shark, according to Chapman.
The biggest distinction between the two species is the dusky shark is leaner and has and has a long upper caudal tail, in which the upper lobe of its tail is longer than the bottom, Chisholm noted. White sharks have homosocial tails, meaning the upper lobe and the lower lobe are almost equal in size.
"If you were swimming and you saw a shark of that size, no matter what species it is, you're probably getting back on the boat," Chapman said.
In 2023, Megan Winton, a senior scientist with the Atlantic White Shark Conservancy, captured video of a dusky shark killing a seal.
Before then, shark researchers knew dusky sharks were scavengers because whale carcasses had been found in their stomachs.
"But this was the first proof that they were actively hunting and catching and eating these seals," Chisholm said. "So it was a big discovery for us."
Researchers from the Atlantic White Shark Conservancy, the New England Aquarium and the Massachusetts Division of Marine Fisheries published their findings in the journal Environmental Biology of Fishes last year.
Dusky sharks migrate to the Gulf during the winter. Between 2003 and 2022, the Mote aquarium did not catch a single dusky shark, Chapman said. But in December 2022, biologists caught two dusky sharks in a row -- both females longer than 10 feet -- further proof that the species is rebounding.
Ever since, Mote researchers have been catching and tagging between two to six dusky sharks every winter, according to Chapman.
"We've started to see them come back, which is fantastic," he said.