Multi-year Research Improves Knowledge Of Sea
Turtle Population
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June 19, 2006
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South
Carolina DNR photo |
The seventh sampling season for a federally funded in-water sea
turtle project designed to gain insight into the population trends,
migration patterns and general health of sea turtles recently
concluded off the coast of Charleston.
Since May 2000, biologists with the S.C. Department of Natural
Resources (DNR) have been using modified shrimp nets to capture sea
turtles and collect a suite of biological data on each turtle before
tagging and releasing them a short while later. During the first
four seasons of the project, trawling was conducted over an
expansive area from Winyah Bay to St. Augustine, Fla., and 936
individual loggerhead sea turtles were captured, of which only 13
have since been recaptured.
In addition to the high catch rates of turtles, low-recapture rates
also illustrated that further research would be needed to determine
whether juvenile loggerheads encountered in coastal waters during
the summer were resident or transient, and whether these animals
returned to the same areas each summer. The research focus shifted
in spring 2004 to a specific location off of Charleston to collect a
suitable number of juvenile loggerheads for satellite tagging.
This year, six juvenile loggerhead turtles were outfitted with
satellite transmitters, which are designed to track the turtle’s
location and diving behavior for up to one year. Since 2004, 24
juvenile loggerhead turtles have been collected through a series of
trawls in the Charleston Harbor shipping entrance channel and
satellite tagged.
Tracks showing the patterns for all of these animals can be viewed
online.
With few exceptions, loggerheads tagged off Charleston between
mid-spring and late summer have remained resident off of the coast
until late fall, though these turtles sometimes moved further
offshore than where the researchers would have encountered them
during their earlier regional trawl survey. Most surprising,
however, is that most of these animals also spend the winter and
early spring off the South Carolina and Georgia coast, in much
colder water than previously reported, and predictably return to
Charleston during April.
According to DNR biologist Mike Arendt, who manages the data for the
project, “It’s pretty wild to watch these turtles spend the winter
at different locations, sometimes hundreds of miles apart, only to
converge back within a few days of each other and to the same
general area where they were caught the previous spring.”
In April 2006, a third dimension to the project was added, a study
of the distributional patterns of elusive adult male loggerhead
turtles, which comprised only 31 of the 936 loggerheads that were
collected during the 2000-2003 regional survey. Because of
difficulties gaining access to adult male loggerhead turtles, only a
handful have ever been monitored with satellite telemetry, and thus,
very little is known about their behavior and distribution patterns.
Given the past successes of this research project, the team was
granted permission to target adult male loggerheads at the Cape
Canaveral, Fla., shipping entrance channel, a known hotspot for
adult males during the spring mating season.
Though it is still early in the monitoring cycle of the adult males
from Canaveral, already the researchers are intrigued by what they
are finding. Of nine adult males which were satellite tagged in
mid-April, seven continue to be tracked daily, a major success story
considering the vulnerability of the satellite transmitters to
physical damage by competitor male turtles during the breeding
season. Of the seven adult males currently being tracked, four have
recently traveled north from Cape Canaveral, as far as the Outer
Banks of North Carolina, while three have continued to be very
resident in the vicinity of Cape Canaveral.
Next April, biologists will return to Cape Canaveral to repeat their
work in order to increase the total number of animals studied as
well as to determine if the same patterns persist in multiple years.
The researchers will also increase efforts to address a fourth area
of uncertainty for sea turtle biologists: the origins and
distributional patterns of sick and emaciated sea turtles, also
referred to as “Barnacle Bills.” A theory regarding these emaciated
turtles is that they become cold-stunned during exposure to cold
winter waters, presumably from more northern areas, and then
passively drift into the southern region until they are so weak that
they strand on area beaches. Limited evidence crediting this theory
was obtained in summer 2005, when a rehabilitated loggerhead caught
by the DNR research team was released with a satellite transmitter
following three months of care at the South Carolina Aquarium, and
the animal immediately returned to North Carolina waters. This
migratory behavior was completely different than patterns observed
for any of the other 17 juvenile loggerheads collected from the same
area.
Over the past six years these researchers and their collaborators
have contributed greatly to the understanding of sea turtle life
history in the Southeast. As DNR biologist Julia Byrd explains,
“Through this program’s collaborative studies not only were catch
rates analyzed, but baseline health parameters, contaminant levels,
sex ratios and the genetic composition of the turtles in the waters
of this region have also been investigated. The results from these
studies will have a large influence on future research and
monitoring of sea turtles throughout these regions.”
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