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Major Hurricanes along the North Gulf Coast of Florida Affect Adult Survival Rates of the Endangered Florida Manatee

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Injured manatee: Contact with a boat propeller injured this manatee. The healed scar is one of the "naturally occurring" marks used to identify this individual. Annual resightings of uniquely scarred animals provide the data to estimate annual survival rates. Photographs are used to document the sightings and verify identifications of individuals in the scar-catalog data base. This female, BS107 (a.k.a. "Phyllis"), has been photographed regularly since 1988 and gave birth to twins in 1991.
A paper entitled "Lower survival probabilities for adult Florida manatees in years with intense coastal storms" by Catherine Langtimm and Cathy Beck, wildlife biologists at the U.S. Geological Survey (USGS)'s Center for Aquatic Resource Studies in Gainesville, FL, was published in the journal Ecological Applications in February.

Understanding how animal populations respond to hurricanes has generally been limited by a lack of critical prehurricane data necessary to make poststorm comparisons. This study presents the first empirical evidence for the storm effects on manatee-survival rates and was based on 19 years of photo-identification data. Identifying and understanding hurricane effects for this species and others is critical for short- and long-term planning by researchers, managers, and policymakers.

The study identified lower survival rates in 1985 with Hurricanes Elena and Kate, in 1993 with the March "Storm of the Century" that impacted the entire east coast, and in 1995 with Hurricane Opal. These storms were category 3 or greater on the Saffir-Simpson scale.

The decreases in manatee survival could be due to direct mortality, indirect mortality, and (or) emigration from the region as a consequence of storms. Future impacts to the population by a single catastrophic hurricane, or by a series of smaller hurricanes, could increase the probability of manatee extinction.

With the advent in 1995 of a new 25- to 50-year cycle of greater hurricane activity and intensity identified by meteorologic researchers, and longer-term change possible with global climate change, the study concludes that it becomes all the more important to reduce manatee mortality and injury from boats and other human causes and to control the loss of foraging habitat to coastal development.

Recent publications on manatees from the Center for Aquatic Resource Studies:

  • Langtimm, C.A., and Beck, C.A., 2003, Lower survival probabilities for adult Florida manatees in years with intense coastal storms: Ecological Applications, v. 13, p. 257-268.
  • Deutsch, C.J., Reid, J.P., Bonde, R.K., Easton, D.E., Kochman, H.I., and O'Shea, T.J., 2003, Seasonal movements, migratory behavior, and site fidelity of West Indian manatees along the Atlantic Coast of the United States: Wildlife Monographs, v. 151, p. 1-77.

Related Web Sites
Center for Aquatic Resource Studies
U.S. Geological Survey (USGS), Gainesville, FL
Ecological Applications
Ecological Society of America (ESA) publication

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