AD 2015 Q4

By Allison Vitsky Sallmon, DVM
Like many kids who grew up in Florida
decades ago, my earliest interactions
with manatees just … happened,
and they did so quietly with a
minimum of fuss. The first “sea
cow” I encountered simply snuffled
toward me in the St. John’s River
while I swam near my parents’ dock. And the last time
I traveled to Crystal River (this is where I date myself),
it was a serene destination with a tiny dive operation or
two, a couple of local hotels and a few snorkelers floating
blessedly far apart from one another. Manatees had plenty
of room to approach humans — or not — as they foraged
in peace. It’s hard to believe that this area and this creature
are now the focus of contention.
But things change, even in Crystal River. Between
2000 and 2010, Citrus County (which encompasses
Crystal River) saw a population increase of more than 19
percent, which undoubtedly included many new residents
dreaming of tranquil days on or near the water. Local
ecotourism has grown even more. Florida’s manatees
gather every winter near freshwater springs and powerplant
outflows where the water is warm (a constant 72°F)
compared with ocean and air temperatures. Crystal
River’s Three Sisters Springs has the greatest freshwater
outflow in the area and a correspondingly large wintertime
manatee population. Visitors swarm the area to visit the
gentle, goofy-looking marine mammals that are a symbol
of Florida’s wildlife conservation efforts. Three Sisters
drew more than eight times as many visitors in 2013 as in
2006. The U.S. Fish and Wildlife Service (FWS) reports
that on the busiest days the springs can get more than 100
visitors per hour, and a brief Internet search reveals pages
of manatee-related activities for sightseers. Snorkeling?
Paddleboarding? Kayaking? If it has to do with viewing
manatees, people will line up to do it.
Manatee protection efforts have been adjusted and
expanded over the past several decades to keep up with
the influx of humans. Created in 1983 to protect Florida’s
endangered West Indian manatees, the Crystal River
National Wildlife Refuge (NWR) limits in-water activities
at the headwaters of Crystal River. Several winter
sanctuaries that ban all human-manatee interaction also
have been established. To prevent boat strikes, authorities
have lowered speed limits and limited watersports zones.
Although “swim-with” manatee permits have been
granted to some tour operators, more anti-disturbance
rules have been put into place over the years (prohibited
activities include pinching and standing on manatees,
suggesting that egregious conduct does take place on
occasion). Last year Three Sisters Springs implemented
additional precautionary measures, including decreased
paddlecraft access and the option to close the area to
the public during extreme cold fronts. But some recent
reports suggest that current guidelines may still fall short.
The Florida Fish and Wildlife Conservation Commission
(FWC) conducts statewide aerial surveys to track manatee
populations one to three times each year. While the
surveys aren’t perfect census tools, they indicate that
manatee numbers are on the upswing — from around
1,200 animals counted in 1991 to more than 6,000 in 2015.
But in Crystal River the increase in manatee numbers
is confined to small areas that are increasingly overrun
with people. Well-meaning as most of us may be, realities
remain: Local boaters want waterway access, local tour
operators want to please tourists, and visitors want to go
home having interacted with a manatee.
As for what the manatees want, we can assume their
primary goals are to eat and survive. Perhaps biology
determines the rest. We should consider a key feature
of manatees’ sensory systems. Their bodies are covered
with vibrissae (tactile hairs), which provide the animals
abundant information about their environment from the
pressure and movement of water.
“Simply put, touch is their ‘super-sense,’” explains
Iske Larkin, Ph.D., lecturer at the University of Florida’s
Aquatic Animal Health program. Martine de Wit, DVM,
of the FWC, concurs, stating, “These are very tactile
animals, and the proximity of lots of people may affect
them more than we can imagine.”
For the manatees, escaping the crowds means
moving to colder water. From a nutritional standpoint,
manatees exposed to water temperatures below 68°F
have much greater caloric needs — up to 50 percent
more according to one researcher — than manatees in
warmer habitats. Below a certain water temperature,
juvenile manatees simply cannot eat enough to survive.
Cold stress is particularly hard on young animals.
“These animals need to eat almost constantly to
maintain their internal temperature, as they cannot
hold heat as effectively as adults,” explains Mike
Walsh, DVM, co-director of the University of Florida’s
Aquatic Animal Health program. “When the springs
get crowded, many manatees will just leave. However,
young manatees can make bad decisions about when —
or whether — to return to warm water.”
When water temperatures drop into the 50s (°F), the
situation becomes more acutely dangerous. “At this
point, manatees get skin lesions that resemble frostbite
in humans,” explains Ray Ball, DVM, medical sciences
director at Tampa’s Lowry Park Zoo. “Manatee blood
vessels are structured in a unique and unforgiving
way to begin with, and their blood is very prone to
coagulation at cold temperatures.”
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