SAVANNAH, Ga. - Wildlife officials and conservationists are seeing fewer newborn right whales than they had hoped to see this winter off the coasts of Georgia and Florida.

Right whales are critically endangered, with experts estimating only about 450 of the giant marine mammals still exist. So conservationists keep a close watch during the winter calving season by conducting daily aerial surveys aimed at spotting whale mothers swimming with their newborns.

So far, researchers have spotted just nine baby right whales more than midway through the calving season, which runs from December through March. About 20 calves are spotted in an average season.

"It's been a slow season for sure," Clay George, lead marine mammal biologist for the Georgia Department of Natural Resources, told the Savannah Morning News.

Hunted the brink of extinction in the 1800s, north Atlantic right whales feed off the coast of New England in the summertime before pregnant females migrate to warmer waters off Georgia and Florida each winter to give birth. It's the only known calving area off the Atlantic coast. Entanglement in fishing gear and collisions with ships now pose some of the greatest threats to their survival.

Some hope remains that calving numbers will improve this year. Spotters have seen at least 10 females that are old enough to give birth but haven't yet been seen with a calf this season.

"That number of potential mothers adds to our hopes that we will be sighting more calves this season," said Patricia Naessig, right whale coordinator for the nonprofit Sea To Shore Alliance.

Biologists from the Georgia DNR, the Florida Fish and Wildlife Commission and the National Oceanic and Atmospheric Administration regularly use darts to collect skin and blubber from individual right whales for genetic testing. That allows researchers to track individuals, build family trees and get a better fix on the population numbers.

Samples have been taken from four calves so far this season. Researchers estimate they've taken samples from about two-third of documented calves since 2006.