Sea turtles are clearly in need of conservation today. However, without data that provides knowledge of their biology, it is very hard to frame appropriate management strategies. Intensive research often needs extensive infrastructure and funding which may or may not be available to all field biologists. Fortunately, even the simplest of monitoring programmes can help collect basic data on various aspects of sea turtle biology, which could be crucial to their conservation.
Simple tools such as tagging have been used for decades to find answers to these questions. In recent times, more sophisticated techniques such as satellite telemetry and molecular genetic analyses have been used to deal with these questions. Such advances in science and technology offer us the chance to understand more about these animals. Go to India research project profiles.
Tagging is particularly useful to study animals at the nesting beach. Identifying an animal uniquely enables us to estimate the number of clutches laid each season. If this is known, beach surveys that only include nest counts can be used to estimate the number of nesting females. Tagging also provides information on time intervals between nesting (inter-nesting interval) and distance between nesting sites (site fidelity). Most turtles generally lay within the same area (0 to 10 km) each time they nest. In some cases, such as with olive ridley turtles in Orissa, they may travel larger distances (a few 100 km) for re-nesting. Some leatherbacks have nested on beaches separated by more than 700 km.
When tags are returned from other areas by field biologists or fishers, it helps in identifying migration routes and foraging grounds of turtles tagged in breeding areas and vice versa. However, long distance returns of tags are usually very low compared to the number of tags applied.
A tag inventory has been established at the Archie Carr Centre for Sea Turtle Research (ACCSTR), University of Florida, Gainesville, to keep a record of all tags used in sea turtle tagging programmes. This database can be accessed at http://accstr.ufl.edu/taginv.html. Tagging programmes should register their tag numbers and codes in this database. Field biologists who encounter or receive information on unidentified tags can search the database to locate the origin of the tag and provide the information to the tagging programme.
Tagging provides information about migration only as far as the sites of tagging and tag recovery, hence allowing inferences about the beginning and perhaps, the end points of the migration. For details of the migratory route, and behaviour during migration, one has to turn to a more advanced technique, namely telemetry. Radio telemetry is a widely used technique in wildlife studies, and has been used with limited results to study turtles within the breeding area. This involves placing a transmitter on the turtle and tracking it with a receiver. However, once a sea turtle begins its (often) long journey to its foraging area, it is impossible to track and follow these turtles. Satellite telemetry solves this problem as the transmitter signal is received by a satellite, and the animals can be tracked wherever they go. This data can be used to trace the precise migratory route of the turtle, and collect associated information such as swim speed and travel rate. Transmitters can be fitted with equipment to provide information on water temperature and activity of the turtle.
Transmitters, also called PTTs (Platform transmitter terminals) are attached to the animal whose long distance movements are to be studied. Once they are turned on, the transmitters send high frequency signals which are received by polar orbiting weather satellites. ARGOS, a French company, has equipment on board these satellites for tracking animal movements. The transmissions are first decoded to identify the transmitter, each of which has a unique code and then the position of the transmitter is calculated. The data are then downloaded by ARGOS. Once the data are received, the latitudes and longitudes can be plotted on a map and the migratory routes of the animals can be traced. A tracking tool is also available at http://seaturtle.org/stat/.
For many years, sea turtle biologists have grappled with questions such as: Are black turtles and green turtles separate species? How closely related are olive and Kemp’s ridleys? From which rookery does a group of foraging turtles derive? Do clutches have multiple paternities? And do turtles return to their natal beaches to nest? Sea turtles have long been believed to nest on their natal beaches, i.e. the beaches where they were born. For many years, this remained mere speculation. Firstly, the hatchlings grow from a few centimeters in size to adults that are many times larger, ranging from the 80 cm ridleys to the 180 cm leatherbacks. Tags that would successfully last through till adulthood (which could take ten or more years) are not available. Secondly, considering that only one in a thousand hatchlings survives till adulthood, the number of tags that would need to be applied to get significant results would be astronomical. In the early 1990s, a technique became available that could successfully address the question of natal homing in turtles – molecular genetic analysis. In simple terms, if turtles did not return to their natal beaches, the genetic markers of the populations would mingle. If however, turtles were faithful to their natal beaches, then markers in different populations would be distinct.
Molecular genetic analysis is useful in investigating the population distribution of highly migratory sea turtles, establishing linkages between feeding grounds and breeding areas. The better understanding of the range of a population of sea turtles can in turn help identify conservation priorities and involve regional partners in collaborative conservation efforts.