Abstract
The Florida manatee, Trichechus manatus latirostris, is an endangered marine mammal inhabiting Florida's marine and fresh waters. There is a great need for data regarding their poorly understood reproductive cycles in order to improve management strategies. The objective of this study was to analyze progesterone patterns from free ranging individuals throughout the female manatee reproductive cycle in concurrence with observed behaviors.
Florida manatees are diffuse seasonal breeders, reproducing during warmer months, but rarely in colder months due to low temperatures and decreased food quality.1 Therefore, manatees should exhibit increased progesterone concentrations during warmer months and decreased concentrations during colder months. It is also hypothesized that nursing will suppress the estrus cycle and weaning will reactivate it. Behavioral signs of mating and high estrogen peaks followed by high progesterone peaks should indicate the individual's time in estrus.
Three female free-ranging manatees were tagged and monitored over a two-year period. Weekly attempts were made to locate each female with a VHF receiver. If located, instantaneous behavior records were taken at ten-minute intervals over one hour followed by an attempt to collect a fecal sample. Sufficient data were available for analysis from one of the three manatees surveyed. Hormones contained in the feces were chemically extracted and progesterone concentrations were measured using an enzyme immunoassay (EIA); Progesterone CL425 (monoclonal UC Davis), intra-assay CV = 7.1%, inter-assay CV = 8.0%. Average fecal progesterone concentrations during colder months (November-March; 280 pg/g, n = 7) were 1.5 fold lower (p = 0.08) than during warmer months (April-October; 430 pg/g, n = 15). Average fecal progesterone concentrations while nursing (291 pg/g, n = 16) were 2.1 fold lower (p < 0.05) than after weaning (623 pg/g, n =6). The fecal progesterone concentration increased by 3.3 fold shortly after weaning when a mating herd was sighted.
These findings support our preliminary data and the hypothesis that a reproducing, wild, female Florida manatee exhibits a trend of higher fecal progesterone concentrations during warmer months and lower concentrations during colder months. Additionally, the results support the hypothesis that nursing may suppress fecal progesterone levels, and the event of weaning may reactivate progesterone production.
Acknowledgements
Funding is provided through the Florida Fish and Wildlife Conservation Commission, Whitney Marine Laboratory for Marine Bioscience, and the University of Florida Aquatic Animal Health Program at the University of Florida College of Veterinary Medicine. Behavior data and fecal samples were collected under UF IACUC number 200802158 and US Fish & Wildlife permit number MA038448-3. We thank the USGS - Biological Resources Division, Sirenia Project; especially Dr. Robert Bonde and Susan Butler for their assistance with tagging and tracking these animals. The authors also wish to thank the Crystal River Wildlife Refuge for assisting in the tagging and tracking of the animals, and Allison Gopaul for assisting in fecal sample preparation and hormone extractions.
Reference
1. Rathbun GB, Reid JP, Bonde RK, Powell JA. Reproduction in free-ranging Florida manatees. In: O'Shea TJ, Ackerman BB, Percival HF, editors. Population Biology of the Florida Manatee, Information and Technology Report 1. Washington, DC: U.S. Department of the Interior, National Biological Service: 1995; p 135–156.