Give Hong Kong's green turtles a fighting chance to survive
Michael Lau says if Hong Kong wants to safeguard its endangered green turtle population, action is needed to protect the waters around the last remaining breeding ground on Lamma
Seven species of sea turtle inhabit the world's tropical and subtropical waters. Six of these are threatened, while the status of the Australian flatback turtle is listed as "data deficient". Sea turtles face a multitude of threats, from being accidentally caught and drowned in fishing nets to the overexploitation of their eggs at their nesting beaches.
Five species of sea turtle can be found in Hong Kong. One of them, the green turtle, actually nests here. This giant used to nest on the beaches of several offshore islands, and the eggs were harvested and sold by local villagers. Now, only Sham Wan on Lamma Island supports a very small breeding population.
A decline in sea turtle populations has been observed in many locations across Asia. One increasingly significant cause is the exploitation of turtles for trade in their products or even in whole specimens.
A report by Traffic, the wildlife trade monitoring network, indicates that there has been an increase in demand for sea turtle products in China. There have also been strong indications that some fishing vessels from China are targeting sea turtles in their operations in tropical Asia. This is reflected by a growing number of cases of Chinese fishing vessels being detained by Southeast Asian countries and protected sea turtles being found on board.
Green turtles are slow to mature: it takes between 26 and 40 years before they are able to breed. Once they reach adulthood, they have few natural enemies and can live and reproduce for a long time.
The most vulnerable stages of their lives come when they are in the egg and when they are small hatchlings. It is estimated that only two to three turtles in every thousand survive to return to their natal beaches to breed.
Their exceptional orientation abilities ensure that they can find their way across vast oceans to return to the natal beach to nest; however, when subject to heavy exploitation, breeding becomes extremely difficult and it takes a long time for a depleted population to bounce back, as there is unlikely to be any "recruitment" from other, healthier populations.
Another special adaption of sea turtles is that their sex is determined by the temperature at which their eggs are incubated. If the incubation temperature is below 29 degrees Celsius, males, predominantly, will be produced, while only females will be produced at temperatures above 30.4 degrees. Rises in temperature resulting from climate change pose a great uncertainty for their future survival.
Green turtles migrate long distances from their breeding sites to feeding grounds, which increases their chance of coming into harm's way. Satellite tracking by Hong Kong's Agriculture, Fisheries and Conservation Department shows turtles can travel several hundred kilometres from Hong Kong, to waters near Hainan Island , eastern Guangdong and Vietnam. Adults feed mainly on algae and sea grass but also eat some invertebrates. They often mistake pieces of floating plastic for squid. Today, ingestion of non-digestible plastics is a common cause of sea turtle death.
Hong Kong's nesting green turtle population now probably consists of just a few adult females. Some years may see zero nesting activity.
In 1999, the government established Sham Wan as a restricted area, with no entry allowed without a permit during the nesting season. The fisheries department also patrols the nesting beach, and when natural incubation of the eggs is deemed too risky, artificial incubation will be carried out.
These efforts have resulted in baby turtles being hatched successfully either naturally or artificially.
However, the weakest link in conserving this species here is that the coastal waters adjacent to the nesting beach at Sham Wan are not protected and are subject to disturbance from people engaging in water sports.
It is in these same shallow waters that male green turtles will wait for the females - to mate with them before they lumber up the beach to lay their eggs.
The waters around South Lamma were identified as a potential marine park or reserve in a previous planning study. Indeed, with the Convention on Biological Diversity being extended to Hong Kong in 2011, we have a responsibility to contribute to the convention's biodiversity targets, one of which states that 10 per cent of coastal and marine waters should be conserved as protected areas by 2020.
To save the remnants of our green turtle population, we should spare no effort to protect the waters off Sham Wan and give these turtles space and time, and thus the best possible chance, to recover.
Michael Lau is senior head of programme for local biodiversity and regional wetlands at WWF-Hong Kong