GPS Tracking Project of the World’s Largest Land Crabs
24 Nov 2016The largest land crab in the world, the coconut crab (Birgus latro), can weigh in excess of nearly nine pounds, and can span as wide as one yard (or 36 inches) across. Once commonly found throughout various tropical Indo-Pacific islands, numbers are rapidly declining due to habitat destruction, and overhunting.
The crab, that was placed on the International Union for the Conservation of Nature’s (IUCN) Red List of Threatened Species back in 1981, is still poorly understood in terms of its basic ecology. This is as a result of a deficit in monitoring and research, and is now something being worked on by a team of researchers.
The team who have travelled to Palmyra Atoll, 1,000 miles south of Hawaii, hopes to ascertain the answers to questions such as:
- Which exact habitats need to be protected to ensure the survival of the species?
- What are the habitat requirements of the crabs?
- How far do these crustaceans travel daily?
Coconut crabs are plentiful throughout this remote atoll, as it is completely uninhabited, apart from the presence of visiting scientists, and research station staff. The team’s goal is to attach 20 radio tags and GPS tracking devices to the crabs with the purpose of tracking their movements throughout the tropical forests that cover the atoll.
The role of the GPS tracking device is to chronicle the crabs’ exact positions every two minutes for a week, and the VHF tag attached to the crabs will emit a radio signal that will allow the crabs to be recaptured when the study comes to an end.
The researchers, comprising of Tim White, a PhD candidate at Stanford’s Hopkins Marine Station, Monterey, California, and Ana Sofia Guerra, a graduate student from the University of California, Santa Barbara, made a 5,600-km journey to Palmyra Atoll.
The team reached the atoll that is made up of various smaller islets, separated by shallow reefs and stretches of water via a motorized skiff. As coconut crabs are most active at night, the team arrived in the evening, with only glowing bioluminescent plankton, a spotlight, and a compass to help them navigate.
Within minutes of setting foot on land, the pair came across the largest coconut crab they’d ever seen. They captured the ten-pound, bright blue crustacean, and quickly decided to attach their first VHF tag, and GPS tracking logger.
The crabs, that have powerful claws that can very easily crush human bone, must be handled with extreme care, however within minutes, the team had tagged their first study subject.
The team are hoping to complete their trip with a far clearer picture of exactly how coconut crabs live their lives in the forest, so methods of their protection can be better understood.
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