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Sea TurtlesKemp’s
Ridley Sea Turtles
Kemp’s Ridley Sea Turtles
Common Name: Kemp’s Ridley
Sea Turtles
Scientific Name: Lepidochelys kempii
Description
Adult Kemp's ridleys, considered
the smallest marine turtle in the world, weigh on average
around 100 pounds (45 kg) with a carapace (top shell) measuring
between 24-28 inches (60-70 cm) in length. The almost circular
carapace has a grayish green color while the plastron (bottom
shell) is pale yellowish to cream in color. The carapace is
often as wide as it is long and contains 5 pairs of costal
"scutes". Each of the front flippers has one claw while the
back flippers may have one or two.
Similar to olive ridleys, Kemp's
ridleys display one of the most unique synchronized
nesting habits in the natural world. Large groups of Kemp's
ridleys gather off a particular nesting beach near
Rancho Nuevo, Mexico, in the state of Tamaulipas. Then wave
upon wave of females come ashore and nest in what is known
as an "arribada," which means "arrival" in
Spanish.
There are many theories on what triggers
an arribada, including offshore winds, lunar cycles, and the
release of pheromones by females. Scientists have yet to conclusively
determine the cues for ridley arribadas. Arribada nesting
is a behavior found only in the genus Lepidochelys.
Female Kemp's ridleys nest
from May to July, laying two to three clutches of approximately
100 eggs, which incubate for 50-60 days. After incubation,
hatchlings emerge weighing about half an ounce (14 g) and
measuring about 1.5 inches (3.8 cm).
Reproduction and Development:
Nesting occurs from April to June during
which time the turtles appear off the Tamaulipas and Veracruz
coasts of Mexico. Precipitated by strong winds, the females
swarm to mass nesting emergences, known as arribadas or arribazones,
to nest during daylight hours. Clutch size averages 110 eggs.
Some females breed annually and nest an average of 1 to 4
times in a season at intervals of 10 to 28 days. Age at sexual
maturity is believed to be between 7 to 15 years.
Range and Population Level:
The range of the Kemp’s ridley includes the
Gulf coasts of Mexico and the U.S., and the Atlantic coast
of North America as far north as Nova Scotia and Newfoundland.
Most Kemp’s ridleys nest on the coastal beaches of the Mexican
states of Tamaulipas and Veracruz, although a very small number
of Kemp’s ridleys nest consistently at Padre Island National
Seashore, Texas. Hatchlings, after leaving the nesting beach,
are believed to become entrained in eddies within the Gulf
of Mexico, where they are dispersed within the Gulf and Atlantic
by oceanic surface currents until they reach
about 20 cm in length, at which size they enter coastal shallow
water habitats.
The Kemp’s ridley is the most seriously endangered
of the sea turtles. Its numbers have precipitously
declined since 1947, when over 40,000 nesting females were
estimated in a single arribada. The nesting population produced
a low of 702 nests in 1985; however, since the mid-1980's,
the number of nests laid in a season has been increasing primarily
due to nest protection efforts and implementation of regulations
requiring the use of turtle excluder devices in commercial
fishing trawls. During the 1999 and 2000 nesting seasons,
more than 3,600 nests and 6,000 nests, respectively, were
deposited on the Mexico nesting beaches.
Habitat:
Outside of nesting, the major habitat for
Kemp's ridleys is the nearshore and inshore waters of the
northern Gulf of Mexico, especially Louisiana waters. Kemp's
ridleys are often found in salt marsh habitats. The preferred
sections of nesting beach are backed up by extensive swamps
or large bodies of open water having seasonal narrow ocean
connections.
Adult Kemp's primarily occupy "neritic"
habitats. Neritic zones typically contain muddy or sandy bottoms
where prey can be found. Their diet consists mainly of swimming
crabs, but may also include fish, jellyfish, and an array
of mollusks.
Depending on their breeding strategy, male
Kemp's ridleys appear to occupy many different areas within
the Gulf of Mexico. Some males migrate annually between feeding
and breeding grounds, yet others may not migrate at all, mating
with females opportunistically encountered.
Female Kemp's have been tracked migrating
to and from nesting beaches in Mexico. Females leave breeding
and nesting areas and continue on to foraging zones ranging
from the Yucatán Peninsula to southern Florida. Some
females take up residence in specific foraging grounds for
months at a time, leading scientists to suggest that females
have a goal-oriented migration, opposed to the suggested wandering
strategy employed by olive ridleys. Kemp's ridleys rarely
venture into waters deeper than 160 ft (50 m) (Byles and Plotkin,
1994).
Newly emerged hatchlings inhabit a much different
environment than adult turtles. After emerging from the nest,
hatchlings enter the water and must swim quickly to escape
near shore predators. There is strong evidence that many sea
turtle species employ an open ocean developmental
stage because encounters with healthy, neonate sea turtles
are extremely rare in near shore waters. Some hatchlings remain
in currents within the Gulf of Mexico while others may be
swept out of the Gulf, around Florida, and into the Atlantic
Ocean by the Gulf Stream.
Juveniles of many species of sea
turtles have been known to associate with floating
sargassum seaweed, utilizing the sargassum as an area of refuge,
rest, and/or food. This developmental drifting period is hypothesized
to last about two years or until the turtle reaches a carapace
length of about 8 inches (20 cm). Subsequently, these sub-adult
turtles return to neritic zones of the Gulf of Mexico or northwestern
Atlantic Ocean to feed and develop until they reach adulthood
(Collard and Ogren, 1990).
Population Trends
The Kemp's ridley has experienced a historical,
dramatic decrease in arribada size. An amateur video from
1947 documented an extraordinary Kemp's ridley arribada near
Rancho Nuevo. It has been estimated that approximately 42,000
Kemp's ridleys nested during that single day! The video also
provided evidence of Kemp's ridley egg collection. Dozens
of villagers are seen on the beach excavating the nests and
subsequent interviews have suggested that 80% of the nests,
about 33,000, were collected and transported to local villages
(Hildebrand, 1963).
This video has also served to measure the
species' collapse. Twenty years after the video was filmed,
the largest arribada measured was just 5,000 individuals.
Between the years of 1978 and 1991 only 200 Kemp's ridleys
nested annually. Today the Kemp's ridley population appears
to be in the early stages of recovery. Nesting has increased
steadily over the past decade. During the 2000 nesting season,
an estimated 2,000 females nested at Rancho Nuevo, a single
arribada of 1,000 turtles was reported in 2001, and an estimated
3,600 turtles produced over 8,000 nests in 2003. In 2006,
a record number of nests were recorded since monitoring began
in 1978; 12,143 nests were documented in Mexico, with 7,866
of those at Rancho Nuevo.
On the Texas coast, 251 Kemp's ridley nests
were recorded from 2002-2006. For the 2007 nesting season,
127 nests have been recorded in Texas, with 73 of those nests
documented at Padre Island National Seashore. Those 127 nests
are a record for the Texas coast, passing the 2006 record
of 102 nests.
Threats
Kemp's ridleys face threats
on both nesting beaches and in the marine environment. The
greatest cause of decline and the continuing primary threat
to Kemp's ridleys is incidental capture in fishing gear, primarily
in shrimp trawls, but also in gill nets, longlines, traps
and pots, and dredges in the Gulf of Mexico and North Atlantic.
Egg collection was an extreme threat to the population, but
since nesting beaches were afforded official protection in
1966, this threat no longer poses a major concern.
For more information, please visit our threats
to marine turtles page
Management and Protection
The recent nesting increase can be attributed
to full protection of nesting females and their nests in Mexico,
and the requirement to use turtle excluder devices in shrimp
trawls both in the United States and Mexico. In 1966, conservation
efforts for the Kemp’s ridley were initiated on the
beach near Rancho Nuevo in Tamaulipas, Mexico. This locale
is the only place in the world where large nesting aggregations
of this sea turtle were and are known to occur. From 1966
to 1987, conservation efforts focused on the area of Rancho
Nuevo with one turtle protection camp. In 1978, the U.S. joined
with Mexico at Rancho Nuevo in a bi-national effort to prevent
the extinction of the Kemp’s ridley. In 1988, this bi-national
program expanded to the south and another camp was added.
In 1989, a third camp was established when the program was
expanded to the north of Rancho Nuevo. By 1997, a total of
seven camps had been established along the Tamaulipas and
Veracruz coasts to allow for increased nest protection efforts.
The Mexico government also prohibits harvesting and is working
to increase the population through more intensive law enforcement,
by fencing nest areas to diminish natural predation, and by
relocating all nests into corrals to prevent poaching and
predation. While relocation of nests into corrals is currently
a necessary management measure, this relocation and concentration
of eggs into a "safe" area is of concern since it
makes the eggs more susceptible to reduced viability due to
movement-induced mortality, disease vectors, catastrophic
events like hurricanes, and marine predators once the predators
learn where to concentrate their efforts.
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