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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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