View the summary of the winter 2009-2010 cold-related unusual
When manatees experience prolonged exposure to water
temperatures below 68°F (20°C), they can develop a condition called
cold-stress syndrome, which can be fatal. The effects of cold
stress may be acute, when manatees succumb rapidly to hypothermia,
or longer-lasting as chronic debilitation. Chronic cold-stress
syndrome is a complex disease process that involves metabolic,
nutritional, and immunologic factors. Symptoms may include
emaciation, skin lesions or abscesses, fat depletion, dehydration,
constipation and other gastrointestinal disorders, internal
abscesses, and secondary infections. Over the past 10 years, the
Florida Fish and Wildlife Conservation Commission's (FWC) Fish and
Wildlife Research Institute (FWRI) has documented several winter
seasons (December-April) with higher-than-usual numbers of deaths
from cold stress: 2000-2001 (32), 2002-2003 (40), 2003-2004 (48),
2004-2005 (45), 2005-2006 (35) and 2008-2009 (69) (FWRI unpublished
data; counts include newborns that might have died from cold
Summary of Winter 2009-2010:
January 2-13, 2010, was the coldest 12-day period on record in
parts of south Florida (Naples, West Palm Beach), with temperatures
at or below 45°F (7.2°C). In central-east Florida, average daily
temperatures during this period were about 15° to 20°F (8° to 11°C)
below normal. The latter half of January was warmer, but unusually
cold temperatures returned around February 7 and lasted through
March. FWC staff made the first cold-related manatee rescue of the
year in Duval County on January 4. The first cold-stress-related
manatee deaths were reported in Brevard and Broward counties on the
east coast on January 7. On January 20, 17 manatees were reported
dead from cold stress, a record number reported on a single day.
During January-April, 58 manatees were rescued and 503 manatee
carcasses were verified in state waters. This carcass count
surpassed the record high annual carcass count of 429 in 2009.
Mortality was particularly high in the central-east and southwest
regions, which include Everglades National Park.
The United States Fish and Wildlife Service and the FWC
consulted the Working Group on Marine Mammal Unusual Mortality
Events, a component of the National Oceanic and Atmospheric
Administration's Marine Mammal Health and Stranding Response
Program. On February 26, the Working Group declared the event to be
an Unusual Mortality Event (UME). Prior to the official
declaration, the response was under way, as the FWC had assembled a
response team to direct the course of the investigation, maintain
close communication among response team leaders, provide
information to partner agencies and organizations, and contribute
to daily operations. Sub-teams included rescue/carcass-salvage
logistics, environmental sampling, aerial survey and ground
monitoring, data management/GIS, necropsy/medical, and media
relations. Throughout the cold event, law enforcement officers,
biologists, and volunteers recovered manatee carcasses. FWC staff
and volunteers transported most of them to FWRI's Marine Mammal
Pathobiology Laboratory for necropsy (non-human autopsy).
As of December 5, preliminary necropsy data indicate 244
cold-stress-related deaths in 2010, which is almost ten times the
five-year average (27) for the cold stress category for the same
portion of the year (January 1 - December 5). Thirteen of these
cold-related deaths were newborns. A record number of 172
cold-related deaths were reported between January 11 and February
9. Most of these manatees appeared to have died from acute
hypothermia, not from chronic debilitating effects of the cold.
This acute cold shock was seen in manatees of all sizes; chronic
cold-stress syndrome usually affects only juveniles. From mid-
February through the first week of April, the carcass count
remained above average, which was mostly attributed to chronic
conditions from exposure to cold. Undetermined causes of death and
unrecovered (but verified) carcass numbers for January-March 2010
were also at a record high (120 and 64, respectively). The
similarity of the timing and location of these carcasses and the
cold-stress carcasses suggests that the majority of the deaths from
unknown causes were also due to cold stress.
The high number of manatee deaths and their wide geographic
extent are of concern, but this and other cold-weather events are
natural occurrences. Our understanding of manatee population
dynamics is based on a combination of ecological information and
mathematical models. To evaluate the effect of this UME on the
Florida manatee population, scientists will need time to observe
and analyze the survival rates of the adult manatees they monitor.
The FWC and partner organizations will use this information to
better understand the roles of various threats and to improve our
ability to forecast population changes. This UME underscores the
importance of warm water to the species. Loss of warm-water habitat
is a significant long-term threat to the manatee population.
Adequate warm-water habitat must be effectively managed in order to
protect Florida's manatees.
View Larger Image in PDF format (546 KB)
Distribution of manatee carcasses reported in Florida, January
11-April 9, 2010. These dates mark the extent of the 2010
cold-related manatee mortality event. Manatees in all regions
except the northwest suffered unusually high mortality.
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