A view from the air--Where have the forests gone? (Sierpe River Area, SW Costa Rica)
Sea turtles are amongst the most fascinating animals on Earth because of the way they have adapted their bodies in order to survive life in harsh, saltwater environments. These various species of sea turtles are distinguishable by appearance, lifestyle and other unique characteristics. Unfortunately, most of the species have been overexploited and now face endangerment in the same habitats that once allowed their populations to thrive. Conservation efforts have been improved over the years, but more drastic measures need to be encouraged if the sea turtles’ future is to be secured.
Turtles and tortoises belong to the order Testudinata, which is divided into two suborders. These suborders, Cryptodira (hidden-necked turtles) and Pleurodira (side-necked turtles), are comprised of about 250 species. Sea turtles belong to the Cryptodirans suborder, consisting of species living throughout the tropical and temperate oceans of the world and most types living on land or in lakes and rivers. (Cogger 108). More specifically, sea turtles are separated into the family Cheloniidae (Loggerhead turtles, Flatback turtles, Green turtles, Hawksbill turtles, Kemp’s ridley and Olive ridley) and the family Dermochelyidae (Leatherback turtle) (Alderton, 175). These seven species of sea turtles reached their peak during the Jurassic and Cretaceous periods, 200 to 65 million years ago (Zweifel 114).
Sea turtles’ anatomical features began evolving about 150 million years ago, when some turtles moved from living on land to living in the sea (Lehrer 92). This unique evolution required the animal to make the necessary adaptations to life in an aquatic, saltwater environment. One change involved the limbs becoming paddle-shaped, in order to push itself through the water. This necessary movement also requires that the forelimbs be more powerfully developed than the hind, a distinction with most other turtles. Since the limbs have evolved to benefit them in the water, this is the only group that must drag its body when on land to lay eggs (Lehrer 93). Another majr evolutionary change took place internally with the lacrymal gland, located in the eye. The high levels of salt in the new aquatic environment caused stress on the kidneys of sea turtles. This adaptation to the environment allows the reptiles to take saltwater into their bodies and then excrete the salts through the lacrymal gland. This conversion from saltwater to freshwater keeps the internal organs from failing and prevents the sea turtle from becoming dehydrated (Alderton 40).
I chose to focus my paper on the Atlantic or Kemp’s ridley (Lepidochelys kempii) species because it is the most critically endangered marine chelonian and predominantly positioned in our Tropical Marine Ecology course’s area of study. This chelonian was named after Richard M. Kemp, a fisherman who located the species in Florida (http://turtles.org/ridleyd.htm). The Kemp’s ridley sea turtle is found mainly in the Gulf of Mexico and surrounding warm Atlantic waters. Occasionally, in the summer and fall seasons, the turtles will migrate up to New England via the Gulf Stream (Conant 76). This sea turtle may have become isolated in this area as a result of the Panamanian land-bridge closure four million years ago (Alderton 116). Kemp’s ridleys are carnivorous animals because the mainstays in their diet include crabs, lobster, snails, jellyfish, shrimp and clams.
Many physical characteristics help to distinguish the Kemp’s ridley species from all other sea turtles. First, it averages 23 to 27.5 inches, distinctively making it the smallest sea turtle. The size of the sea turtle caused it to receive the nickname “Bastard turtle” because of the belief that it is a hybrid between Loggerhead turtles and Green turtles (Conant 77). Even though Kemp’s ridley is the smallest sea turtle, it has an unusually large head. The head contains a recognizable “beak” that is used to catch and separate hard-shelled prey (http://www.cresli.org). Kemp’s ridley is also the only sea turtle with an almost circular carapace (upper part of the shell) because it is almost as wide as it is long (Conant 77). This carapace will change from a gray-black color at birth to a lighter gray-olive color at maturity. The plastron (lower part of the shell) will develop from gray-black to a cream-white color (http://turtles.org/ridleyd.htm).
After mating offshore, female sea turtles leave their aquatic environment in order to lay their eggs, while males remain in the ocean their entire lives. These females always return to the same beach for nesting. Extensive research has been done to try to determine if the sea turtles will only lay eggs at the beach in which they were born. It is believed that newly hatched sea turtles will eat some sand to imprint the smell and taste, allowing it to find the same beach in the years to come (Cogger 115).
The Kemp’s ridley has numerous unique characteristics relating to its nesting habits. First, this species only utilizes one nesting beach, Tamaulipas, Mexico, which is located on the eastern coast. This adds to its vulnerability of extinction because hunters can easily determine when and where the eggs are laid (Zweifel 114). The Kemp’s ridley females usually nest three times from April through July, with a 10 to 28 day resting period in between. The nesting process, which averages the laying of 110 eggs, may take place in a range from every year to every three years (http://dep.state.ct.us). Contrasting it from all other sea turtles, the Kemp’s ridley is a diurnal nester, as opposed to a nocturnal nester, which means they lay their eggs during the daylight hours. In order to elude predators and have a higher chance for survival, the nesting procedure must be done in a swift manner, causing the turtles to frantically dig and crawl atop each other. The Kemp’s ridleys collectively come ashore for the arribada, or “arrival”. In 1947, this communal nesting used to reach numbers of 42,000 at one time. Recently, with the decreasing population, the arribadas have reached levels as low as 400 females per season (http://www.nmfs.noaa.gov). The small size and light weight is an advantage of the Kemp’s ridley sea turtles. This allows for a smaller track to be left in the sand, which can lead predators to the nesting site. Sea turtles also prefer to nest when winds are strong, so that their track and scent is dispersed, further helping to conceal the nesting location (Alderton 119).
On December 2, 1970, the Kemp’s ridley was placed on the endangered list, a condition that has since remained unchanged. The endangerment is further evident because the overall population is believed to be less than 5,000, even though Kemp’s ridleys have received protection in Mexico since the 1960’s (Alderton 119). Predators are the main cause of this drastic reduction in population. Humans are their largest predator, but other animals such as coyotes, wild dogs and feral hogs also place a high risk on the Kemp’s ridleys’ survival. Collecting the eggs, fishing, killing the mature turtles for meat and directly taking them for indigenous use are a few of the ways that human involvement in the oceanic world has impaired the population (http://www.nmfs.noaa.gov). Even though these examples have led to a dramatic reduction, the shrimp trawlers have made an even greater impact. Before regulations were placed on shrimping, each year an estimated 500 to 5,000 Kemp’s ridleys found themselves caught in trawls, crab traps and gill nets, where they would later drown. The mortality is much higher for Kemp’s ridleys than other sea turtles because they feed mainly on the crustaceans being caught, as opposed to other turtles that favor marine vegetation (Alderton 120). It seems that a slow recovery is on its way due to stricter regulations in regards to shrimp trawlers. Turtle Excluder Devices (TEDs) must now be used in order to reduce the number of turtles that are trapped and drown, by recognizing objects larger than shrimp in the net. The shrimp fleets have been drastically reduced and the near shore water off of Tamaulipas, Mexico is closed during the nesting season, although it is loosely enforced (http://www.nmfs.noaa.gov).
Human population growth and coastal development are yet additional risks to Kemp’s ridleys. As the Mexican population grows and more people desire to live in areas close to the beach, the single nesting site of the Kemp’s ridley is becoming increasingly threatened. Kemp’s ridleys are also threatened by marine pollution, debris and dredging. These threats are still linked to humans because they are direct results of human actions. The nesting area and the two main feeding sites are in locations of high-density offshore oil extraction. Oil exploration and production leave Kemp’s ridleys at an elevated level of vulnerability to oil spills. Debris floating in the Gulf of Mexico, such as hooks, cans, cellophane or rope, can easily be ingested or cause entanglement of the sea turtles. The dredging operations may directly kill Kemp’s ridleys or cause degradation of their habitat. The channeling that is a result of the dredging leads to decreased water quality and altered current flow, which will change the migratory habits of the turtles (http://www.nmfs.noaa.gov). These examples are not the only causes of concern for Kemp’s ridleys, but they are the threats that pose the greatest problem with decreasing population numbers.
Luckily, conservation efforts have become more apparent in recent years and in some areas are proving to be beneficial. The Caribbean Conservation Corporation is the oldest sea turtle conservation organization in the world. It runs many tracking programs and focuses on the education, research and passing of conservation actions in order to increase sea turtle population (http://www.cccturtle.org/). One such effort is the Recovery Plan for U.S. Population of Kemp's Ridley Sea Turtle by the U.S Fish and Wildlife Service and National Marine Fisheries Service in 1992. The goal of this plan is to move Kemp’s ridleys from the endangered list to the threatened list (http://turtles.org/ridleyd.htm).
In 1947, research shows that there were 162,400 mature Kemp’s ridleys. Less than 30 years later, in 1974, the same study shows that the population level had dropped to 4,872 (http://www.seaturtle.org/). Currently, numbers are hard to determine, but it is estimated that less than 5,000 Kemp’s ridleys remain (Alderton 119). Hopefully, since hundreds of programs and projects have been enacted over the years, each one will make a small difference and together progress will be achieved. Individually we can all make a difference through actions such as donations, letters to government officials regarding conservation efforts, promoting the usage of TED’s and respecting the Kemp’s ridleys’ habitat. If humans want to be able to study and experience the unique aspects of Kemp’s ridleys, we must make an extreme effort in the near future to protect the remaining sea turtles, so their populations can once again flourish.
Alderton, David (1988) Turtles & Tortoises of the World, Facts on File Publications, New York. Pg. 40, 115-122, 175.
Caribbean Conservation Corportaion. http://www.cccturtle.org/. World Wide Web.
Cogger, Harold (1998) Encyclopedia of Reptiles & Amphibians; Second Edition, Academic Press, San Diego. Pg. 108-117.
Conant, Roger and Joseph T. Collins (1991) Peterson Field Guide; Reptiles and Amphibians of Eastern & Central North America; Third Edition, Houghton Mifflin Company, Boston. Pg.75-78.
Connecticut Department of Environmental Protection. http://dep.state.ct.us/burnatr/wildlife/factshts/krsturt.htm. World Wide Web.
Kemp’s Ridley. http://turtles.org/ridleyd.htm. World Wide Web.
Kemp’s Ridley Sea Turtle. http://www.cresli.org/cresli/turtles/kemprid.html. World Wide Web.
Lehrer, John (1993) The World of Turtles and Tortoises, Tetra Press, New York. Pg.92-101.
Office of Protected Resources. http://www.nmfs.noaa.gov/prot_res/species/turtles/kemps.html. World Wide Web.
Sea Turtles. http://www.seaturtle.org/. World Wide Web.
Zweifel, Richard (1992) Reptiles & Amphibians, Smithmark Publishers, New York. Pg. 114-117.
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