Near-record numbers of manatees have died in Florida waters in early 2011, the second straight year of above-average deaths, alarming officials who are also puzzled by a surge in dolphin fatalities along the US Gulf Coast.

Of the 163 manatee deaths recorded from January 1 to February 25, 91 of them have been blamed on cold water temperatures off the southern US state, where normally temperate weather draws the protected sea creatures during winter months, according to the Florida Fish and Wildlife Conservation Commission.

Manatees live near the coastline, and when weather turns cold they often shelter near springs or in warmer discharge canals at power plants to avoid the condition known as "cold stress," which can weaken and eventually kill the aquatic mammals.

A record 185 manatees died in Florida during the same period last year, according to the commission.

Authorities at the National Oceanic and Atmospheric Administration are also investigating the huge increase in baby dolphins found washed up dead along the US Gulf Coast, in the first birthing season since the BP oil spill disaster.

Eighty-three bottle-nosed dolphins, more than half of them newborns, were found dead in January and February along the coasts of Texas, Louisiana, Mississippi, Alabama and Florida, where millions of barrels of oil from a leaking undersea well poured into the Gulf of Mexico over three months.

"Direct or indirect effects of the BP/Deepwater Horizon spill event are... among the potential reasons for this increase in strandings," NOAA spokeswoman Kim Amendola said Wednesday.

"We have not found an indicator on what could be causing these deaths," but said several factors could have contributed to the deaths including biotoxins, "red tide" algal blooms, or infectious disease, she said.

"We are following the situation closely," she added.

The oil from the spill spread through the water column in massive underwater plumes and also worked its way into the bays and shallows where dolphins breed and give birth.

Dolphins breed in the spring -- around the time of the April 20 explosion that brought down the BP-leased drilling rig -- and carry their young for 11 to 12 months.

Birthing season goes into full swing in March and April.