Abstract: The Florida manatee is an aquatic herbivore found in tropical, coastal waterways. This endangered species becomes sexually mature at sim2 to 5 years of age. Reproductively active adults often form mating herds, consisting of one focal female pursued by several males. Understanding Florida manatee (Trichechus manatus latirostris) reproductive biology is important for establishing population models, making management decisions, and recognizing differences between healthy and unhealthy states. Field and necropsy data indicate that manatees do not have well-defined breeding seasons and are diffuse in their breeding patterns. They exhibit reproductive activity throughout the warm months, having peaks during spring and lulls during winter months. Monitoring male testosterone concentrations in both wild and captive populations can provide direct comparisons of physiological data on the reproductive status of these animals. The objectives were to (1) validate the use of a commercial testosterone radioimmunoassay kit for measuring faecal concentrations of the parent steroid in male Florida manatees, (2) identify biologically meaningful distinctions between gender and levels of maturation measured with faecal testosterone concentrations, and (3) identify seasonal hormone fluctuations. Of individual adult mean values, 62% of males had higher testosterone concentrations than all adult females measured. The total range of male faecal testosterone concentrations measured was 120.8–36,240 ng/g dry weight; whereas, females ranged 120.8–5,919 ng/g. Seasonal fluctuations in hormone concentrations were observed in captive manatees with peaks during spring and/or fall, supporting the hypothesis that Florida manatees are a diffusely seasonal breeding species. Results indicate that radioimmunoassays of faecal hormones can be a useful, non-invasive tool for monitoring testosterone concentrations in Florida manatees, enhancing the accuracy of current monitoring methods of using behavior or morphometrics. This can be particularly helpful in field sites where animals are not captured for health assessments and water clarity limits observations of the animals, which is typical of most water bodies manatees inhabit.


Document Type: Research article

DOI: 10.1578/AM.31.1.2005.52

Page Numbers: 52 - 61

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