TITLE: MANATEES: STUDY SEES RISK, HOPE: A TINY INCREASE IN THE DEATH RATE COULD DOOM THE CREATURE, BUT A SLIGHT IMPROVEMENT WOULD ASSURE THE SPECIES' SURVIVAL.
BYLINE: Victor Hull REGIONAL REPORTER
EST. PAGES: 2
DATE: 08/21/97
DOCID: SSTA72330312
SOURCE: Sarasota Herald-Tribune; SSTA
EDITION: All; SECTION: A SECTION; PAGE: 1A
(Copyright 1997)
Just a slight increase in the number of manatees killed each
year by boats would be enough to doom the species to extinction,
according to a ground-breaking scientific analysis.
The analysis, by two University of Florida researchers and a federal biologist, concluded that 14 to 17 more manatee deaths per year, or a 10 percent increase over current levels, would "guarantee" extinction in less than 1,000 years.
"That sounds like a long time," said Lynn Lefebvre,
the manatee project leader for the U.S. Geological Survey's biological
resources division in Gainesville. "But ecologically, that's
a drop in the bucket. You have to look at the bigger picture."
The increase would amount to only one additional manatee death
per year in each of several populous coastal counties where manatees
tend to congregate.
Given Florida's rising population, and the soaring number of
boats plying the state's waters, such an increase in manatee mortality
is conceivable. Without the effective enforcement of regulations
to protect manatees, the species' demise is inevitable, the study's
authors concluded.
"It's a very predictable outcome," said the report's
co-author, Stephen Humphrey, interim dean of the University of
Florida's College of Natural Resources and Environment.
But if measures to protect manatees from boat collisions, pollution
and habitat destruction reduced their deaths annually by 10 percent,
the species' survival would be assured, the analysis found.
"If we can change attitudes and behavior to be manatee-friendly,
we can coexist with manatees forever," Humphrey said.
That's a big "if." Efforts to impose boat speed limits
or restrict the development of marinas and boat ramps have been
met with various degrees of resistance. Many large metropolitan
areas, including the Tampa Bay area, have yet to adopt manatee
protection plans.
Enforcement of the restrictions in place is sporadic. The number
of boats registered in Florida has soared nearly 25 percent in
the last decade, but the number of law enforcement officers on
the water has declined in the last three years.
The analysis, published in the scientific journal Conservation
Biology earlier this year, presents the most comprehensive view
of the statewide condition of the manatee population to date.
The technique used in the analysis is one commonly used by
biologists to predict the fate of various species, but this is
the first time it has been applied to manatees.
Previously, scientists were unable to use the population model
because they couldn't reliably determine the ages of dead manatees.
That hurdle was overcome by one of the co-authors of the report,
Miriam Marmontel, whose doctoral research at the University of
Florida included the finding that a bone in the manatee skull
can be used to pinpoint the age of an individual animal.
Using data gathered from manatee carcasses statewide over a
15-year period, the researchers gleaned information on the reproductive
and mortality rates of manatees to get a better handle on the
age characteristics of the overall manatee population and its
growth rate.
They concluded that the Florida manatee population from 1976
to 1991 remained essentially stable. The scientists then considered
how the population would react to several scenarios, such as random
epidemics, weather catastrophes and increases or decreases in
deaths caused by humans.
Manatees, like other large mammals, take longer to reach sexual
maturity and reproduce more slowly than many animals. A female
manatee may produce only one calf every three years. Thus, an
increase in the number of manatees killed could have a severe
impact on the species' ability to reproduce.
The small overall population - estimated at 2,000 to 3,000
animals - makes manatees more vulnerable to catastrophic natural
events, such as cold snaps or red tide outbreaks like the one
that killed more than 150 manatees last year.
The reproduction rate of manatees can't be increased, and humans
can't control the weather. But if they reduced the number killed
by boat collisions, the statistics show that more of them would
reach maturity and reproduce.
Still, some boating enthusiasts say the restrictions in place
already are excessive. In Sarasota County late last month, opponents
of a manatee protection zone on the Myakka River presented the
County Commission with a petition bearing nearly 1,000 signatures
from people who want reduced speed limits repealed.
"In essence, they've shut the river down for human use,"
said Budd Hegele, who owns a house by the Myakka River and complains
of being stopped by Florida Marine Patrol officers enforcing the
speed limit. "They've made the manatee into a sacred cow.
It's been totally absurd, the limits to which it's taken. They
don't want humans using the waterway."
Manatees, cuddly looking whiskered creatures often referred
to as "gentle sea cows," are perhaps Florida's best-known
endangered species. Their images are emblazoned on everything
from license plates to coffee mugs, making them the poster species
for the state's environment. The large animals feed only on aquatic
plants, such as sea grass. Because they move slowly and frequent
shallow areas along the coast and in canals, they're vulnerable
to boats.
The new analysis confirms mathematically what many manatee
experts have long assumed about a species that has been listed
by the federal government as endangered for the last 30 years.
"Our work shows as clearly as anyone can possibly show
from a neutral standpoint that the state policy of planning and
implementing boat regulations is justified, and, if properly implemented
and enforced, it should work," Humphrey said.
Manatee mortality These figures show the number of manatee
deaths in Florida over the past 10 years:
TOTAL DEATHS DEATHS BY BOAT
1987 114 39
1988 133 43
1989 168 50
1990 206 47
1991 174 53
1992 163 38
1993 145 35
1994 193 49
1995 201 42
1996 415 60
1997 *111 26*
Through June
SOURCE: Florida Department of Environmental Protection
ART: PHOTO (C);
Caption: A manatee comes up for air in Sarasota Bay. A new study uses a population model to predict the fate of the species.
STAFF PHOTO/ALLISON LONG
OTHER TERMS: TAG: 9708210312