Hurricanes and Florida Manatees
 

In the 1980s and 1990s severe coastal storms impacted the Florida panhandle and north Gulf Coast. Research by the Sirenia Project, USGS Florida Integrated Science Center, identified lower apparent adult survival rates for manatees of the region during three years with extreme storms rated Category 3 or higher on the Saffir-Simpson hurricane scale: 1985 with Hurricanes Elena and Kate, 1993 with the March "Storm of the Century", and 1995 with Hurricane Opal. Mechanisms that could have led to lower estimates of survival included death from stranding, injury from debris, being fatally swept out to sea, or displacement into poorly monitored areas due to storm-generated longshore currents or storm-related loss of habitat.

In the unprecedented hurricane seasons of 2004 and 2005, seven major hurricanes impacted areas of Florida encompassing three regional manatee subpopulations. The effects of these hurricanes on manatee survival rates remain to be seen. Mark-resighting photo-identification data are being collected to estimate survival rates during 2004 and 2005. The magnitude of effect should vary with the destructiveness of the storms, which depends on wind speed, size, storm wave and surge height, speed of forward motion, and near shore bathymetry that would affect storm surge and storm currents. Other factors can also exacerbate or ameliorate risk to the manatee population, such as density of manatees within the strike area, the number of storms within a season, protective features of the coastline such as barrier islands, or occurrence of other mortality factors during the same year, such as toxic red-tide blooms or severe cold weather. Florida manatees, endangered and living at the northern limit of their natural range, are subject to multiple sub-lethal stresses that can have chronic and debilitating effects, possibly making individuals more vulnerable to storm death.

For further information please contact Cathy Langtimm. Email: Cathy_Langtimm@usgs.gov

Seven hurricanes ploughed through manatee habitat in 2004 and 2005. This map depicts the tracks of the hurricanes that impacted manatee habitat. Hurricanes Charley, Frances, Ivan and Jeanne hit in 2004, and Hurricanes Dennis, Katrina and Wilma hit in 2005. The names of all 7 of these storms have been retired by the World Meteorological Organization because of the extensive devastation they caused.
 

CURRENT RESEARCH

HURRICANE EFFECTS 2004-2005

C. A. LANGTIMM, M. D. KROHN, J. P. REID, B. M. STITH, AND C. A. BECK. 2006. Possible effects of the 2004 and 2005 Hurricanes on Manatee Survival Rates and Movement. Estuaries and Coasts 29(6A):1026-1032. (pdf: ESTU2006_29_6A_1026_1032.pdf)

   Abstract -- Prior research on manatee (Trichechus manatus latirostris) survival in northwest Florida, based on markresighting photo-identification data from 1982–1998, showed that annual adult apparent survival rate was significantly lower during years with extreme storms. Mechanisms that we proposed could have led to lower estimates included stranding, injury from debris, being fatally swept out to sea, or displacement into poorly monitored areas due to storm-generated longshore currents or storm-related loss of habitat. In 2004 and 2005, seven major hurricanes impacted areas of Florida encompassing three regional manatee subpopulations, enabling us to further examine some of these mechanisms. Data from a group of manatees tracked in southwest Florida with satellite transmitters during Hurricanes Charley, Katrina, and Wilma showed that these animals made no significant movement before and during storm passage. Mark-resighting data are being collected to determine if survival rates were lower with the 2004 and 2005 storms.

Open access to all of the papers published in this special issue of Estuaries and Coasts "Hurricane Impacts on Coastal Ecosystems" can be found at:
 http://estuariesandcoasts.org/contents/ESTU2006_29_6A.html

Meyers, J. M., C.A. Langtimm, T.J. Smith, III, and K. Pednault-Willett.  2006. Wildlife and habitat damage assessment from Hurricane Charley: recommendations for recovery of the J. N. "Ding" Darling National Wildlife Refuge Complex.  USGS Open File Report 2006-1126.  http://sofia.usgs.gov/publications/ofr/2006-1126/index.html

PAST RESEARCH

HURRICANES 1982-1999

Ecological Applications: Vol. 13, No. 1, pp. 257–268.

LOWER SURVIVAL PROBABILITIES FOR ADULT FLORIDA MANATEES
IN YEARS WITH INTENSE COASTAL STORMS

Catherine A. Langtimm and Cathy A. Beck

  Abstract -- The endangered Florida manatee (Trichechus manatus latirostris) inhabits the subtropical waters of the southeastern United States, where hurricanes are a regular occurrence. Using mark–resighting statistical models, we analyzed 19 years of photo-identification data and detected significant annual variation in adult survival for a subpopulation in northwest Florida where human impact is low. That variation coincided with years when intense hurricanes (Category 3 or greater on the Saffir-Simpson Hurricane Scale) and a major winter storm occurred in the northern Gulf of Mexico. Mean survival probability during years with no or low intensity storms was 0.972 (approximate 95% confidence interval = 0.961–0.980) but dropped to 0.936 (0.864–0.971) in 1985 with Hurricanes Elena, Kate, and Juan; to 0.909 (0.837–0.951) in 1993 with the March "Storm of the Century"; and to 0.817 (0.735–0.878) in 1995 with Hurricanes Opal, Erin, and Allison. These drops in survival probability were not catastrophic in magnitude and were detected because of the use of state-of-the-art statistical techniques and the quality of the data. Because individuals of this small population range extensively along the north Gulf coast of Florida, it was possible to resolve storm effects on a regional scale rather than the site-specific local scale common to studies of more sedentary species. This is the first empirical evidence in support of storm effects on manatee survival and suggests a cause–effect relationship. The decreases in 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 series of smaller hurricanes, could increase the probability of extinction. With the advent in 1995 of a new 25- to 50-yr cycle of greater hurricane activity, and longer term change possible with global climate change, it becomes all the more important to reduce mortality and injury from boats and other human causes and control the loss of foraging habitat to coastal development.

Full Scientific Paper:

Langtimm, C. A., and C. A. Beck. 2003.  Lower survival probabilities for adult Florida manatees in years with intense coastal storms. Ecological Applications 13:257-268. <pdf: Langtimm&Beck Ecol. Apps.pdf>

Short popular press abstract of the research:

Major Hurricanes along the North Gulf Coast of Florida Affect Adult Survival Rates of the Endangered Florida Manatee.  Soundwaves – The Monthly Newsletter of Coastal Science.
http://soundwaves.usgs.gov/2003/05/pubs.html

Most recent analysis:

Langtimm, C. A., C. A. Beck. H. H. Edwards, K. J. Fick-Child, B. B. Ackerman, S. L. Barton, and W. C. Hartley. 2004.  Survival estimates for Florida manatees from the photo-identification of individuals. Marine Mammal Science 20:438-463.  <pdf: mmsc-20-03-438..463.pdf>
 

ADDITIONAL HURRICANE RESEARCH BY USGS-FISC

Erosion and damage to US coast lines. Research by the USGS Coastal and Marine Geology Program of the Florida Integrated Science Center will provide important information on storm forces that may impact manatees. Before and after photographs of hurricane damaged coastlines in 2004 and 2005 can be found at http://coastal.er.usgs.gov/hurricanes/.

USGS Science: Before, During and After the Storm
http://www.usgs.gov/hazards/hurricanes/2007/default.asp