Call of the wild:
Green turtles have strong migratory and navigation capability. They will swim to a feeding ground hundreds or thousands of kilometres away. When they reach adulthood, females will return to the beach where they were hatched to lay their eggs.
Keeping track:
Signals from satellite transmitters attached to the turtles’ shell help researchers record the migratory pathway, the number of dives and average dive time.
On the menu:
The green turtles were fed fresh vegetables, shrimps and fish daily during their temporary stay at Wetland Park.
Green turtles released to the sea
May 10, 2011
With satellite transmitters attached to their backs, four juvenile green turtles were recently released back into the ocean. Agriculture, Fisheries & Conservation Department Wetland & Fauna Conservation Officer Connie Ng will track the turtles’ signals and hopes to see them again on Lamma Island, with nests of their own at Sham Wan.
The turtles were left at a veterinary clinic last October. Agriculture, Fisheries & Conservation Department staff collected them, and nurtured them at Hong Kong Wetland Park. There, they had a daily meal of fresh vegetables, shrimps, fish and squid - a menu that reflects their natural diets.
After five months of monitoring and veterinary care, each turtle had gained three to four kilograms. Their original weights have increased from 12kg to 38kg, to around 16kg to 42kg. Mature adults can grow to 200kg.
“From their positive response to feeding, active swimming activity and strong repulsive force when we handle it, we can tell they are healthy and in good shape, ready to return to the sea,” Ms Ng said.
Unique ID
Sea turtles are highly endangered species and in Hong Kong, all sea turtles are protected. The green turtles are the only species known to breed locally, on Lamma Island’s Sham Wan beach. AFCD staff have taken DNA samples from the turtles, to discover whether they were born in Hong Kong.
It is difficult to know their exact age, although they are still juveniles, aged from 10 to 20 years. Since they are not yet sexually mature, the staff cannot tell from their appearance whether they are male or female.
Ms Ng said they hoped to release the turtles in their top physical condition, “so that they carry out their ultimate goal in life which is to propagate the next generation and also perform their essential role in an ecosystem.”
Before their release, staff inserted a microchip and attached metal tags on their four flippers for future identification.
“The metal tag bears the origin of place, in this case Hong Kong. It also contains a unique number, similar to our identity card number, that gives each turtle an identity. When some researchers encounter these turtles later, they will know the origin of these turtles and contact us.”
Keeping track
A satellite transmitter has also been attached to each turtle’s shell. “We can detect its migratory pathway and determine its ultimate foraging ground. This information is essential for us in formulating conservation measures regarding this endangered species,” Ms Ng said.
The transmitter batteries can last for 100 days on average, but it is difficult to predict how long the transmitters will remain fastened to the turtles. When the turtles swim near the coast, the transmitters may get caught on rocks, or the turtle may hide in a cove, causing the unit to detach.
Nevertheless, Ms Ng sees value in satellite tracking. Since 2002, the department released 21 sea turtles to the sea, and tracked some of them. Records suggest their feeding grounds are as far away as Shanwei in Guangdong Province, the East Sand Islands (Dongsha Islands) in the South China Sea, Hainan Island, and Vietnam’s Dao Bach Long Vi beach off Haiphong.
Call of the wild
The four green turtles were prepared for their release into the wild on May 5, in the southern waters of Hong Kong near Po Toi. On the journey by boat out to sea, AFCD staff covered them with wet towels to keep them moist, and covered their eyes to keep them calm. Still, they seemed excited, as though they could smell the tang of the seawater.
The seawater temperature was about 20 degrees Celsius, which would make it easy for the turtles to adapt to their new surroundings. The waters around Po Toi are rich in food sources such as sea grass, seaweed, fish and marine life that appeal to the green turtles.
After switching off the vessel’s engine, Ms Ng and her colleagues carefully lifted the turtles one by one and gently released them into the sea. As they disappeared into the water, she looked forward to receiving signals from the transmitters on their backs.
Circle of life
Ms Ng is impressed by the turtles’ strong migratory capability. After returning to the sea, they not only have to feed themselves, but overcome challenges. Turtles may mistake a floating plastic bag for a jellyfish, eat it, and get sick. Sharks, boats, nets and other debris all pose deadly threats.
If all goes well, the four turtles will swim to a feeding ground which may be hundreds or even thousands kilometres away from the beach where they were born. When they mature, they may one day return.
“If these four green turtles were really born in Hong Kong, when they grow to 20 to 30 years old and become adults, female turtles will return to Sham Wan of Lamma Island to lay eggs to propagate their next generation, to help sustain this endangered species in our region.”
Ms Ng encourages people to support sea turtle conservation, by joining the Hong Kong Wetland Park volunteer scheme. Groups remove garbage and weeds in Sham Wan periodically to maintain the beach where the turtles nest and the eggs hatch, and the cycle begins anew.
It is an offence to take, possess, willfully disturb, sell, import or export any part of a sea turtle and its nest or egg. Report any sea turtle sightings by calling 1823 or contact the AFCD’s Wetland & Fauna Conservation Division (Monitoring Section) by e-mail to faunaenq@afcd.gov.hk .
