Marine turtles in SE Asia are in dire need of conservation action. With long maturation periods and low survival, they have extremely slow replenishment rates. A population which has been depleted can take several centuries to recover. However, understanding the needs of the turtles also depends heavily the understanding of the extent of habitat use and distribution, which can only be determined through complex research projects involving at-sea population dynamics, genetics, and satellite tracking. By tracking marine turtles through the SE Asian region we aimed to raise the collective awareness of their plight and to provide the concrete linkages at an international level on which Malaysia may develop conservation agendas linked with other neighboring countries to which turtles migrate, including Indonesia, the Philippines, Taiwan and Vietnam.
MRF has established through its laparoscopy project on Mantanani that juvenile turtles recruit there from their post-hatchling neritic drifting life stages at some 30 cm in length, and reside there for some 5-6 years before they subsequently depart to secondary foraging grounds – presently unknown.
Although some turtles are recaptured after 550–600 days, the majority of recaptures suggest that residence times may be shorter than this (around 329 days). To put this into context, marine turtle hatchlings typically leave the beach and are floating in oceanic gyres for 5-6 years, then settle at one or several foraging grounds while growing another 20-25 years before reaching sexual maturity. MRF’s Mantanani project identified, through genetics the origin of the turtles and through laparoscopy and mark-recapture studies, that the turtles are primarily female and spend 6-7 years at Mantanani. The question now is where do they spend the rest of their juvenileand subadult years, before returning to lay eggs?
This can normally be deduced through satellite tracking of juveniles from their known foraging grounds to determine their subsequent movements. The process is, in brief, as follows: A small watertight transmitter with sufficient battery reserve is safely attached to the back of a turtle. When the animal surfaces to breathe, data transmissions are sent to sensitive receivers aboard polar-orbiting satellites. This information is then relayed to ground processing stations that calculate the turtle’s location. The advantages of using satellite tracking are its continuity over time, the capability for remote monitoring, and vastly lower logistics costs.
This project tracked small (40-60 cm CCL) green turtles as they departed Mantanani to identify the location of the secondary foraging areas, to identify the critical overseas migration routes and nearshore habitats favoured by the turtles, which can then help management and conservation activities potentially through spatial or temporal area closures. We selected the largest turtles we could capture, with a view that these would be the most likely to depart to secondary feeding grounds. Unfortunately, after an entire year of tracking, none of the five turtles decided to leave, but the project did accumulate a massive amount of data on the localised movement patterns which can be used in zoning and delineation of a protected area around the island.
This work was sponsored by the Shell Sustainable Grants programme, the Taiwan Bureau of Forestry and the Save our Seas Foundation.