Already facing population losses due to slow reproductive rates, the marine mammals cannot sustain the increasing death toll exacted yearly by boats and personal watercraft in much of Florida, the report's author said.
"If boat mortality rates continue to increase at the rates observed since 1992, the situation in the Atlantic and Southwest regions is dire, with no chance of meeting recovery criteria within 100 years," said Michael Runge of the federal Patuxent Wildlife Research Center in Laurel, Md.
Regulators, wildlife activists and boating rights proponents have haggled over boosting protections for manatees, listed as endangered by both state and federal code.
The Patuxent report is an addendum to protection plans being hammered out by federal officials. Spurred by a lawsuit filed by manatee advocates, regulators plan to issue a new set of safeguards Monday.
Manatees continue to take large losses from collisions with boats and personal watercraft. Such incidents killed a record 95 manatees in Florida last year, following an average of 80 such deaths in the previous three years, state data show.
"If you want to save the manatee, you have got to bring that watercraft-related mortality under control," said Eric Glitzenstein, a Washington, D.C. attorney who led the legal action for manatee activists. "If not, it's a prescription for disaster."
Boating groups argue regulators would be better served to consider the effect of habitat loss and natural factors that kill manatees, like cold stress or sporadic episodes of red tide. Red tide is blamed for at least 60 manatee deaths off southwest Florida in the past two months.
"No matter what, though, they want to put all the manatee mortality on the backs of boaters," said John Kinney, vice president of Standing Watch, a boating advocacy group.