Manatee (Trichechus manatus) encounters and research vessel effects in the Drowned Cayes, Belize, Central America

Bilgre, Barbara 1

Between July 28, 2000 and February 22, 2001, 73 manatee (Trichechus manatus) surveys were conducted across 42 days in the Drowned Cayes, Belize, Central America. Manatees were encountered in 89% of the surveys. One hundred ten sightings produced a field count of 216 manatees including 10 older calves and 17 yearlings. Surveys were conducted from three different 8 m boats, each utilizing a 75 hp outboard motor, and included opportunistic searching while the boat was in motion (46% of all sightings), and dedicated searching in 41 different locations with the boat stationary and motor turned off (54% of all sightings). The mean number of manatees per sighting was 2.02, though manatees were not typically interacting with each other when more than one manatee was in an area.

To determine potential effects of the research vessel on manatee behavior, I analyzed encounters of 82 manatees, in groups of 3 or less, where the boat was within 50 m of the manatees. Boat activities included motoring, drifting, poling, and tied, and the manatee responses were swimming toward, away from, ignoring, or observing the boat. Manatees ignored the boat more than any other response during each of the four boat activities. Manatee responses to boat activity were significantly different for the entire dataset (c2 = 20.3, 9 df, P = 0.05). When the dataset was partitioned by year, manatee responses to boat activity was significantly different in 2000 (c2 = 24.7, 9 df, P = 0.05), but not in 2001 ((c2 = 6.4, 9 df, P = 0.05).

Results of this study on manatee distribution and abundance, and manatee responses to boats may aid the Government of Belize and NGOs in the improvement of Manatee Tour Guide training since manatee-watching is one of the favored marine activities of tourists visiting Belize.