(CNN) The U.S. Fish and Wildlife Service has proposed to remove the West Indian manatee from the endangered species list and reclassify it as "threatened" after "significant improvements" in its population and habitat conditions.

The portly creatures were among the first species added to the list in 1972. There were only an estimated 1,267 manatees in Florida when the agency began aerial surveys of the population in 1991. Today, there are more than 6,300 in Florida, a 500% increase in the species population in the state, the service said.

"The manatee's recovery is incredibly encouraging and a great testament to the conservation actions of many," Cindy Dohner, the Southeast regional director, said in a news release Thursday. "Today's proposal is not only about recognizing this progress, but it's also about recommitting ourselves to ensuring the manatee's long-term success and recovery."

The announcement is the latest chapter in a decade-long battle to remove the manatee from the endangered species list. The designation came with federal restrictions on such things as boat speed and waterfront development that are credited with protecting the species and reversing its decline.

The Florida Home Builders Association sued the U.S. Fish and Wildlife Service in 2005, demanding a review of the endangered species list. The review concluded in 2007 that manatees could be reclassified from "endangered" to "threatened."

'Good' news and 'bad' news

When the service failed to act on its own recommendation, residents in Crystal River formed the organization Save Crystal River and filed a petition in 2012 and two lawsuits seeking reclassification to keep additional restrictions from being added, at the request of environmentalists.

"The good news is that the manatee population is increasing and federal officials are finally acknowledging this fact," said attorney Christina Martin, with Pacific Legal Foundation, a libertarian-leaning watchdog group representing Save Crystal River. The group also represented Florida Home Builders Association.

"The bad news is that federal officials took so long to accept the good news about the manatee's improvement," Martin said in a statement. "We are glad to see that the manatee is doing well, but all taxpayers should demand that the government do much better, going forward, in following the requirements of the Endangered Species Act."

If the manatee is no longer endangered, Brevard County Commissioner Curtis Smith wants to get rid of slow speed zones for boats that took effect in the 1990s to protect the slow-moving manatees from fast boats. Smith says the restriction was based on emotion for the lovable sea cow, not science.

Two Florida lawmakers, Sen. Jeff Brandes and Rep. Larry Ahern, have introduced legislation to study the effectiveness of boating speed zones.

What the change would mean

Conservation groups greeted the news with guarded optimism, questioning the wisdom of applying the status to the entire West Indian species, which includes manatees in the Caribbean and Central and South America.

The Fish and Wildlife Service is "happy with the status quo, but the threat is still out there, and it's not going away," said Katie Tripp, director of science and conservation for Save the Manatee Club . "You don't celebrate when you're not done with the game. There's a lot more work to be done to safeguard the habitat, to get manatees removed from the Endangered Species Act altogether."

The act defines an endangered species as one currently in danger of extinction throughout all or a significant portion of its range. A threatened species is one that is likely to become endangered within the foreseeable future.

The manatee also remains protected under the Marine Mammal Protection Act.

A 90-day comment period began Friday, during which the public is invited to submit scientific or technical feedback to help the service reach its final decision on the proposal. If approved, the new classification is not expected to take effect until 2017.

The proposal to downgrade the manatee to "threatened" will not change federal protections credited with reversing the species' decline, according to the service. Those measures include regulated boat speed requirements and habitat protection.

"The manatee is one of the most charismatic and instantly recognizable species," said Michael Bean, principal deputy assistant secretary for Fish and Wildlife and Parks at the Department of the Interior.

"It's hard to imagine the waters of Florida without them, but that was the reality we were facing before manatees were listed under the Endangered Species Act. While there is still more work to be done to fully recover manatee populations, their numbers are climbing and the threats to the species' survival are being reduced."