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Potentially Misidentified Species:
Ridley Sea Turtle
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
The loggerhead turtle is circumglobal, and inhabits continental
shelves, bays, estuaries, and lagoons in temperate, subtropical, and tropical
waters throughout the world. In the Atlantic, the loggerhead turtle's
range extends from Newfoundland to as far south as Argentina, with no clear
home-ranges defined to date (Lowe et al. 1990). During the summer,
nesting occurs in the lower latitudes, but not in the tropics. The worlds’
largest nesting population is found on the beaches of Oman. The second
largest nesting group is found along Florida's East coast, and it is with this
stock that the U.S. Fish and Wildlife Service is primarily concerned.
Loggerheads have been seen in estuaries as far north as New England and the
Canadian Maritime Provinces. Nesting is common from Florida through North
Carolina, but again, the majority of loggerheads are found in Florida.
Southern Japan is the only known
breeding area in the North Pacific. In the eastern Pacific, loggerheads
have been sighted from Alaska to Chile, with occasional sightings also reported
from coastal Washington. The majority of west coast sightings involve
juveniles spotted off the California coast.
IRL Distribution:
Caretta caretta occurs throughout the
Indian River Lagoon.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Caretta caretta becomes reproductively active at about 80 cm SL
carapace length (Ehrhart 1983). A long lived species, it is estimated to live in
excess of 50 years (Lutz and Musick 1997).
Abundance:
The loggerhead turtle was listed by the U.S. fish and Wildlife Service as
threatened in June, 1970, and its status has remained unchanged. Several nesting
subpopulations of loggerheads in the western North Atlantic have been identified
based on genetic research. The Northern Subpopulation occurs from North
Carolina to Northeastern Florida, and produces approximately 6,200
nests/year. This subpopulation declined throughout the mid-1980s, and
thereafter no population trends have been detected. Recent surveys of
South Carolina nesting beaches (utilized by more than 30% of the nesting
Northern Subpopulation) indicate a downward trend, and thus the subpopulation is
apparently stable or declining.
The South Florida Subpopulation, occurs
from just north of Cape Canaveral, Florida and extends to Naples on the west
coast of Florida. The South Florida Subpopulation appears to have shown
significant increases over the last 25 years, suggesting the population is
recovering. An increase in the number of adult loggerheads has been
reported in recent years in Florida waters, however, there has been no
detectable increase in the number of benthic juveniles. Since loggerheads
take approximately 20-30 years to mature, the effects of decline in immature
loggerheads might not be apparent on nesting beaches for decades. If real,
this decline of juveniles would signal an overall population decline.
Loggerhead populations in Panama, Mexico, the
Bahamas, Cuba, Honduras, Colombia, Israel, Turkey, Greece, and Japan, have
been declining in recent years, and can be primarily attributed to human
impacts. Coastal development, increased human use of nesting beaches, and
pollution cause the most severe impacts to loggerhead nest sites, while shrimp
trawling negatively impacts loggerheads in open waters. Shrimping is
thought to have played a significant role in the worldwide population declines
observed for the loggerhead.
Locomotion:
Primarily swimming; walks while nesting on ocean beaches
Reproduction:
Caretta caretta reaches sexual maturity at 12-35 years, with Lutz and
Musick (1997) reporting 25-35 years. Copulation occurs at sea at no particular
time of day or night. Nesting occurs throughout the summer, predominately
at night on ocean beaches with well drained sand dunes. Females use their
flippers to dig nests in the soft sand, and deposit clutches of approximately
100-120 eggs into the nests. After nesting, females cover the eggs with sand and
return to the water. Eggs require up to 60 days to develop before hatching.
Females may nest 2 - 4 times per season, with 4 nests per season reported by
Hopkins and Murphy (1984). Two and three-year nesting cycles have been reported.
Several factors affect the sexual determination of the hatchlings but much of it
can be accounted for by nest sand temperature. The pivotal temperature for this
species is approximately 29.0 °C. Lower temperatures encourage male
development, while warmer temperatures influence the development of females.
Mrosovsky and Provancha (1992) found hatchlings at Cape Canaveral were
predominately females (80-95%) over a five year study.
IV. PHYSICAL TOLERANCES
Temperature:
Optimum temperature range of both juveniles and adults
is subtropical and warm temperate.
V. COMMUNITY ECOLOGY
Trophic Mode:
Caretta caretta is omnivorous, with a diet
that includes sponges, crabs, clams, mussels, various fish. It is also known to
eat jellyfish, seaweed and seagrass (Ernst and Barbour 1989). Mendonca and
Ehrhart (1982) reported that the predominant food item found in Mosquito Lagoon
loggerheads was Limulus polyphemus, the horseshoe crab. Recent studies by
Provancha et al. (1997) indicate this prey item is in severe decline.
Competitors:
The loggerhead is the most abundant of the sea turtle species in Florida
waters, however, it most likely competes with other sea turtles for food.
Habitat:
The loggerhead wanders throughout marine waters
in its range. It enters bays, lagoons, and the mouths of rivers. There are
essentially four habitats along the Florida coast used by loggerheads. Nesting
adults utilize ocean beaches to deposit their eggs for incubation. Considerable
nesting occurs along the IRL beaches each summer between April and September.
About 98 % of all sea turtle nests are those of loggerheads (Provancha and
Ehrhart 1987). Hatchling sea turtles emerge from the nesting beach and enter the
sea, swimming out to the sargassum driftlines where they find shelter and food
(Carr 1986). The post-hatchling size class of 20-40 cm, previously known as the
"lost year", drifts its way to the eastern Atlantic where it forages
and grows along the Azores and Canary Islands. The IRL estuary provides
developmental habitat for subadult animals, 50 to 80 cm SL carapace length, (Ehrhart 1983, Provancha et al 1997). Netting surveys in the late 1970's, 1990's
and various cold-stunning episodes (see species report on the Green turtle) have
yielded basic data about the lagoon population (Witherington and Ehrhart 1989,
Provancha et al 1997). The loggerhead displays some degree of residency in the
lagoon but appears to migrate to and from the ocean more than the Green turtle.
Activity Time:
Loggerhead turtles are seen on land almost exclusively in the evening hours,
but are active throughout the day.
VI. SPECIAL STATUS
Special Status:
Threatened/Endangered
Notes on Special Status:
Caretta caretta is listed as threatened by U.S. Fish & Wildlife
Service. The most significant threats to loggerhead populations are
coastal development, commercial fisheries, and marine pollution.
Benefit in the IRL:
Aesthetic value; may also be good indicator species whose population
trends are reflective of habitat degradation.
VII. BIBLIOGRAPHY
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Report by: J. Dineen,
Smithsonian Marine Station
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Page last updated: July 25, 2001
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