2012 analysis shows reduced estimates of long-term risk, but mortality events since then raise questions
The risk of extinction for the endangered Florida manatee appears to be lower, according to a new U.S. Geological Survey led study.
Based on the data available in 2012, the long-term probability of the species surviving has increased compared to a 2007 analysis, as a result of higher aerial survey estimates of population size, improved methods of tracking survival rates, and better estimates of the availability of warm-water refuges.
USGS scientists, working with colleagues from several other agencies and universities, used the manatee Core Biological Model to analyze the long-term viability of the manatee population in Florida, and to evaluate the threats it faces. A similar analysis completed in 2007 was used by the U.S. Fish and Wildlife Service as part of its 5-year Review of the status of manatees.
“Our analysis using data from 2007 estimated that there was nearly a nine percent chance of Florida manatee numbers falling below 250 adults over the next 100 years on either the Atlantic or Gulf Coast,” said Michael Runge, a USGS research ecologist and lead author of the study. “The current analysis, using data available in 2012, has the estimate dropping to a fraction of one percent, but we need to be cautious in our conclusion, because the analysis did not include several mortality events that have occurred since then.
The mortality events Runge was referencing were cold winters, loss of seagrass in prime habitat, and a red tide event, all of which affected the population.
“Although the estimated status in 2012 was better than in 2007, questions still remain about the population effects of the more recent cold-related mortality events in the winters of 2009-10 and 2010-11,” Runge said. “The 2012 analysis also does not account for the extensive loss of seagrass habitat in Indian River Lagoon in 2011 and 2012 nor the severe red tide event in the Southwest region of Florida in 2013.”
The potential effects of these events will be analyzed in the next update of the Core Biological Model, which is underway in collaboration with Florida Fish and Wildlife Research Institute and Mote Marine Laboratory, and is expected to be complete within the next year.
The major threats to long-term survival of Florida manatees remain boat-related deaths and loss of warm-water winter habitat. In the Southwest region, an increasing frequency of red-tide deaths also warrants concern.
Manatees are large, gentle, herbivorous, slow-moving mammals. They are entirely aquatic, and their range is limited by temperature. Manatees cannot survive for extended periods in water colder than about 17°C (63°F), and prefer temperatures warmer than 22°C (72°F). Manatees live in shallow fresh, brackish, and marine aquatic habitats, traveling readily among them. In Florida, they travel considerable distances during the winter to access warm water refuges, such as artesian springs and the heated discharges of power generating plants. Some individuals also travel long distances during the warm season.
The publication “Status and threats analysis for the Florida Manatee (Trichechus manatus latirostris), 2012,” USGS Open-File Report 2015-1083, by M. C. Runge, C. A. Langtimm, J. Martin, and C. J. Fonnesbeck is available online.