ST. PETERSBURG — A record number of newborn manatee calves turned up dead last year, but the state's manatee biologists cannot explain why.
In all, 101 of the 337 carcasses that scientists collected in 2008 were very young calves, the Florida Fish and Wildlife Research Institute in St. Petersburg announced Monday. By comparison, they found 59 dead calves in 2007, and 70 in 2006.
That nearly a third of all dead manatees were newborn or stillborn calves poses a baffling mystery for the state's necropsy laboratory — a sort of CSI for sea cows — located on a corner of the Eckerd College campus.
"It is a matter of concern," said Martine DeWitt, the scientist in charge of the lab. But she said she could draw no conclusions about what happened.
Manatee calves weigh about 60 pounds at birth and may stay with their mothers for up to two years. When they die at or near birth, the cause is often unknown.
The culprit may be stress from cold weather, pollution, noise or disease. They might have been poisoned by Red Tide. Sometimes a young manatee may have been orphaned and thus unable to survive alone — something that leaves no marks on the dead body.
The increase in newborn deaths could be due to an increase in the number of calves, DeWitt said, or it could be that the lab did a better job of finding the dead ones. The third possibility: "There could be more calves dying."
Three of the dead calves turned up off Pinellas County, with six off Hillsborough County and one in Pasco County. The most, 34, were found in Brevard County.
The necropsy lab also determined that 90 of the 337 manatees had been killed by speeding boats. That's the third-highest figure for watercraft-related manatee deaths in the past decade, a jump from the 73 killed by boats in 2007. The record, 95, was set in 2002; and in 2006 boaters killed 92 manatees.
Seven of the boat-related deaths occurred off Pinellas, while one occurred in Hillsborough's waterways. The most were in Lee County, which had 14.
The increase in dead newborns does not appear to be connected to the increase in boat-related deaths, DeWitt said. Only six of the manatees killed by boats were nursing females, she said, which would indicate that only a few manatee calves were orphaned by boaters.
But Katie Tripp, the director of science and conservation at the Save the Manatee Club, suggested there might be a subtle connection.
Although manatees can live to be 60, the lab's own records show that most female manatees that have been found dead were younger than 10, Tripp said. That means they have time to produce only one calf before they die, "and first-time mothers are often less successful at raising their young," she said.
Although no one knows for sure how many manatees swim in Florida's waterways, in 2001 scientists counted 3,300 of them, the most ever. Subsequent counts found lower numbers.
Manatees have been listed as endangered since the first federal endangered species list came out in 1967.