FIXED-WING AIRPLANE VERSUS HELICOPTER SURVEYS OF MANATEES (TRICHECHUS MANATUS)

The abundance of manatees, as with most marine mammals, is difficult to determine because they are visible for only short periods of time while at the surface of the water. Aerial surveys are generally considered to be the most accurate method of counting manatees, although there is no doubt that some undetermined proportion is missed. A Bell 47G helicopter was used to obtain a "truth count" to compare with counts made from a Cessna 172 fixed, high-wing airplane. The experiment was conducted at two different sites and on five consecutive days at each site. The first location was Crystal River, which is a clear, spring-fed river that flows about 11 km into the Gulf of Mexico on the central west coast of Florida. The second site was an 8-km-long section of the Indian River, which is a large, turbid estuary adjacent to Cape Canaveral on the east coast of Florida. Although the results cannot be used to assess the effectiveness of fixed-wing aerial censuses for determining manatee abundance, the data show that there is no significant advantage of using helicopters over fixed-wing airplanes for manatee counts in clear or turbid water situations.