Studies of the West Indian Manatee: Anna Maria to Venice (Florida)
Kreckman, Todd A.
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West Indian manatees (Trichechus manatus) typically depart the waters extending from Anna Maria Island, Florida, to Venice, Florida, when the water temperature reaches 16º C and return in the spring when the water temperature rises in the bays of this area. Attempts to accurately determine the population size and distribution of these animals have only recently been initiated (Hartman, 1984). Three manatee programs using aerial surveys conducted in the study area during the 1970's compiled non-winter sightings of only twenty animals. Twenty-five flights averaged 21.5 manatee sightings (n=314) per survey in 1985 (Patton, 1985). From January-December 1985, 138 sighting events occurred in 81 hours of active surveying; manatees were sighted in groups of 1-12 animals, of which 8% were calves. Continued studies were needed to provide data for determination of the stability and actual size of this manatee population. The present study is intended as a follow-up to the 1985 Patton study prepared for the Florida Department of Natural Resources. Twenty flights from March-December 1986 averaged sightings of 13.5 animals (n=269) per survey. In 95 hours of active surveying 136 sighting events were recorded. Numbers of manatees in each sighting event ranged from 1-10 animals; 6.7% were calves. The decrease in the average number of manatees seen per flight from the 1985 study to the 1986 study may be a result of poorer sighting conditions experienced in 1986, but a reduction in the number of large groups (mating herds) may be a significant factor. Five areas of regular or recurring non-winter sightings identified in 1985 were comparably important in 1986: the southeast corner of Anna Maria sound; a large area between Tidy Island and Longboat Pass; the Buttonwood Harbor area; inside Midnight Pass; and the Roberts Bay, situated east of Siesta Key.