LIFE HISTORY AND POPULATION BIOLOGY
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.
Primarily swimming; walks while nesting on ocean beaches
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.
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