The Connecticut River, from its mouth in Old Lyme and Old Saybrook to the Holyoke Dam in Massachusetts, would be one of several areas designated as a “critical habitat” for the endangered Atlantic sturgeon under a proposal set to be finalized as early as next week.

The National Marine Fisheries Service last year published a draft proposal for the critical habitat designation, a component of the Endangered Species Act, which requires more intensive environmental studies before any federally funded project could be undertaken in those areas, said Jennifer Goebel, spokeswoman for the New England office of the fisheries service.

“Any project that is federally funded or federally permitted would have to go through a higher level of scrutiny to make sure it doesn’t adversely impact or destroy the habitat,” she said Wednesday.

The pending designation provides further support to opponents of a Federal Railroad Administration plan for a tunnel under the Connecticut River as part of a bypass project. That plan, proposed in 2015, was effectively abandoned in a decision by the railroad administration on Wednesday.

Goebel said the timing of the critical habitat designation with the proposed rail project was coincidental. The timing of the designation, she said, was set by the requirements of the Endangered Species Act that “critical habitat” areas be established within three years of species being declared endangered. The Atlantic sturgeon became an Endangered Species in 2012. An ancient species on the brink of extinction, Atlantic sturgeon can live up to 70 years and grow to weigh up to 400 pounds.

The fisheries service received more than 1,900 public comments on the draft rule. The final version is being simplified from the draft version, Goebel said.

"The rule is still undergoing review, so it's premature to discuss any other possible changes," she said.

The proposed “critical habitat” areas would include portions of the Penobscot, Kennebec, Piscataqua, Merrimack and Androscoggin rivers in Maine, New Hampshire and Massachusetts; the Hudson River in New York; sections of several rivers that feed into the Chesapeake Bay; and the section of the Connecticut River. The importance of the Connecticut River came to the attention of the fisheries service in 2014, after a Connecticut fisheries biologist found juvenile sturgeon in the lower river. Research done on sturgeon caught by Tom Savoy of the state Department of Energy and Environmental Protection’s Marine Headquarters in Old Lyme concluded that the fish had been born in the river, the first time a breeding population had been found there in decades. Savoy's research was funded by Connecticut Sea Grant.

Goebel said that while proposed rule would impact construction projects, there would be no new restrictions on commercial or recreational fishing in those areas.

“It also doesn’t create any new preserves or refuges,” she said.

The presence of endangered Atlantic sturgeon in the lower Connecticut River was among arguments made against the railroad plan by groups including the Connecticut Audubon Society and its Roger Tory Peterson Estuary Center in Old Lyme. Claudia Weicker, chairwoman of the Board of Directors of the Peterson center, said the railroad administration “overlooked” the sturgeon when the proposal was developed, but was made aware of it in comments submitted by her group.

“We obviously support the critical habitat designation for the sturgeon and for a number of other fish that it will protect as well,” including the short-nosed sturgeon and American shad, she said.

If the rail project had gone ahead, she said, it would have had to comply with strict guidelines for the timing of construction, the types of equipment that could be used and the level of vibration and noise created.

Old Lyme First Selectwoman Bonnie Reemsnyder said she is pleased that the critical habitat designation will be finalized.

“This gives us another good reason to protect the river and not to do any more harm to it,” she said.

j.benson@theday.com