Life History: Sea Turtle Decline

The number of sea turtles present in all the World's oceans is declining.

Film evidence from the major nesting beach of Kemp's Ridleys at Rancho Nuevo, Mexico, indicates that 40,000 females nested there in a single day in 1947. Monitoring of this beach showed about 1,300 females nesting in 1966, since 1967 to 1970 only a few nesting aggregations (called arribadas) of 2,000-2,500 turtles have been reported. Since 1978 all nests have been counted and numbers have declined steadily by about 14 nests per year, with the current level of nesting less than 1% of the estimated nests deposited in 1947 (Decline of the Sea Turtles: 47).

Anecdotal evidence indicates that sea turtles were once very abundant, so abundant in fact, that there are published historical notes indicating one could walk ashore on the backs of turtles and that turtles were captured and stowed on sailing ships to be used for food on transoceanic trips. Local anecdotal stories abound about being able to see many turtles nesting in a given night on Georgia's sandy beaches.

Data gathered on Little Cumberland Island, Blackbeard Island, and Wassaw Island, Georgia, indicates a clear decline of 3% per year for nearly thirty years. Overall Georgia decline is now about 1.5% per year (and is statistically significant). There is some evidence of the Georgia decline lessening and leveling out, but until the curve turns upward (and is statistically significant) all efforts to preserving sea turtles in the northern Loggerhead subpopulation of the Carolinas-Georgia- Northern Florida should continue unchecked.

Personal observation of various species of sea turtles nesting in many other areas leads scientists to conclude that sea turtle populations are generally declining around the world.

Populations of Leatherback sea turtles in the Pacific have declined in the last decade to approximately 10% their former level, a population crash that is well documented. Pacific Leatherbacks are now critically endangered and may not recover to former population levels.

Loggerhead stranded on St. Catherines Island with no evidence of injury or disease; this turtle probably drowned in a shrimp net.

The rapid decline of the size of the population of Kemps Ridley sea turtles, the slow, but steady decline of the Loggerhead sea turtles in Georgia and South Carolina, and observational data of the decline of other sea turtles has led conservationists and scientists to the conclusion that sea turtles are in danger of becoming extinct.

All sea turtles are now listed as endangered species or as threatened species.

Threats to Sea Turtles
The Decline of the Sea Turtle documents the many factors that are driving sea turtles toward extinction. These factors are now well documented and include natural causes and human causes.

The death of sea turtles caused by various natural factors that have been around for a long time including:

• Predation
• Diseases and Parasites
• Other nesting sea turtles
• Vegetation Erosion, Accretion, and Tidal Inundation
• Heavy Rains
• Thermal Stress
• Old Age

The death of sea turtles due to human interactions has significantly increased in the past 50 years and includes (from Decline of the Sea Turtles) the following threats and take (number of deaths).

Systematic study of sea turtle injuries and deaths have been sparse. April Norem (2006) systematically studied injuries of sea turtles at the St. Lucie Nuclear Power Plant, in Florida. She developed a Sea Turtle Injury Identification System for use in her study and advocated its use.

Numbers of Loggerhead sea turtles killed by shrimp fishing have been dramatically reduced in the past five years by installation of turtle excluding devices (TEDs) on shrimp nets and by increasing the size of TED trapdoors in 2004, showing that humans and sea turtles, or other endangered species, can live in harmony with one another, if we study and understand the ecology and life history of the organisms AND resolve to accommodate other organisms with which we share the Earth.

When turtles strandings become extreme, shrimping is attenuated or closed. This graph shows that sea turtle deaths rapidly decrease with the closure, then just as rapidly increase again when shrimping resumes. (From National Park Service).

The Sea Turtle Stranding Network (STSSN), established in 1980, documents all sea turtles found stranded on US beaches, transports live stranded turtles to rehabilitation facilities, and salvages dead turtles for necropsy and research. One of the primary threats to sea turtles is the shrimp trawler fishery. Data collected in Texas, and replicated in Georgia, indicates that when trawling is suspended (called a closure) the strandings of sea turtles rapidly declines. Sea turtles killed by trawling are mostly healthy individuals that are simply drowned by being trapped under water for to long.

Marine turtles are protected species under the jurisdiction of two U.S. government agencies, the National Marine Fisheries Service (NMFS) and the U.S. Fish and Wildlife Service through the Endangered Species Act of 1973 and the Marine Mammal Protection Act of 1972.