The debate over how best to protect the dusky shark — which can migrate hundreds of miles in a season but whose juveniles return every summer to the mid-Atlantic — highlights the complicated task of recovering shark species. (Andy Murch/Getty Images/Visuals Unlimited)

The government plans to require almost all sharks landed by recreational fishermen off the Atlantic Coast and the Gulf of Mexico to measure at least eight feet from nose to fork in the tail, a move that some recreational fishermen said will end their sport but that conservationists say is needed to save an imperiled species.

The debate over how best to protect the dusky shark — which can migrate hundreds of miles in a season but whose juveniles return every summer to the mid-Atlantic — highlights the complicated task of helping shark species recover.

The National Oceanic and Atmospheric Administration has prohibited the catching of dusky sharks since 1999, but scientists found their population to be so depleted that they would need 100 years to recover.

The dusky shark, which averages nearly 12 feet in length and 400 pounds, takes two decades to reach sexual maturity and has small litters every three years, which makes it vulnerable to overfishing. Separately on Thursday, the environmental group WildEarth Guardians petitioned to list the dusky shark under the Endangered Species Act.

“They are going to be rebuilding for a very long time,” said Karyl Brewster-Geisz, one of the agency’s fishery management specialists. She added that officials are “disappointed that overfishing is still occurring, even though fishing is prohibited.”

While the new assessment found that some other species — such as the sandbar shark and the blacktip shark — are recovering, NOAA officials said they needed to impose some broader restrictions to address accidental catches of dusky sharks. Brewster-Geisz said dusky sharks end up on long lines set for other species, and recreational anglers sometimes mistake them for other types of sharks.

“It’s not an easy species to identify,” she said, adding that researchers estimate they will have to cut fishing mortality by two-thirds to recover dusky sharks.

But Mark Sampson, a charter boat captain based in Ocean City, said increasing the recreational landing requirement from a minimum of 41 / 2 feet to eight feet “is effectively going to shut down the recreational fishery” because blacktip sharks rarely reach eight feet and other species at that length would weigh hundreds of pounds.

“It just about blew me away,” said Sampson, who sits on the outside panel that advises NOAA Fisheries on managing migratory species such as sharks. “I’m all in favor of doing what it takes to protect dusky sharks. However, this isn’t the way to do it.”

Sampson, who also runs Ocean City’s annual shark tournament each June, said he believed NOAA was overestimating how many dusky sharks were accidentally being caught by recreational vessels.

Brewster-Geisz described the proposed rules as “science-based management.”

The draft regulations — which apply to 15 types of small and large coastal sharks — will also call for periodic closures of a month or two of commercial long-line fisheries off the East Coast in areas where dusky sharks are likely to die when caught on hooks set for other open-ocean species, such as tuna. The guidelines are subject to public comment until Feb. 12 and will be finalized by the end of April.

While shark fishing is not a major commercial activity off the U.S. coasts, it remains an active recreational sport. Recreational anglers landed about 16,260 coastal sharks in 2010, according to NOAA, while commercial vessels landed more than 104,000 that year.

“The challenge with dusky sharks is that they have such a different life history than these other species they’re being caught with,” said University of Victoria marine biologist Julia Baum, who has studied dusky sharks and other species swimming off the East Coast. She added that fishery managers were trying to figure out, “How do you protect them when you still have a viable fishery for these other species?”

Because it may take dusky sharks years to recover even after restrictions are put in place, Baum added, “it sets up this situation that’s ripe for conflict.”

Taylor Jones, WildEarth Guardians’ endangered species advocate, argued that only federal protection under the Endangered Species Act would ensure a viable dusky shark population.

“Sharks, the wolves of the sea, are key strands in the ocean’s web of life,” Jones said. “Human exploitation and persecution are driving many shark species to the brink of extinction.”

NOAA spokeswoman Monica Allen said the agency would examine the petition’s claims once it received it, “While we have not yet seen the petition on dusky sharks, we will review it carefully once we have it.”