Battling the odds
The discovery of eggs from a green sea turtle has raised awareness of the need to conserve Hong Kong's coastlines. Nick Gentle reports
News late last month that a clutch of 60 baby green sea turtles had been successfully hatched in Hong Kong was a welcome respite from the more or less constant stream of bad news the city hears about its environment. That the eggs were discovered on Tai Long Wan beach in Sai Kung, a place not previously recognised as a nesting site, was even more of a positive because according to villagers, it had been more than 40 years since sea turtles had visited the beach, which is popular with campers and surfers alike.
'Basically, that means the nesting turtles had disappeared, or at least spent a great deal of time away,' says Cheung Ka-shing, wetland and fauna conservation officer for the Agriculture, Fisheries and Conservation Department (AFCD).
Green sea turtles return to their natal beach, the place they were born, to breed. After mating in coastal waters, the female will go ashore, dig a nest and lay an average of 100 to 120 eggs.
Mr Cheung says it is possible the turtle that visited the beach on the night of September 22 may have come from a clutch of eggs laid the last time turtles were seen nesting there.
Five of the seven species of sea turtle have been seen in Hong Kong waters, but the green turtle is the only one known to nest on the city's beaches.
'Here in Hong Kong, we used to have quite a lot of sea turtle nesting sites, but now there is only one regular site, at Sham Wan [aka Turtle Beach] on Lamma Island,' Mr Cheung says. However, no turtles have been seen laying there since 2003.
'So it is good to find nesting sites at other beaches. We are now wondering if there are other places in Hong Kong where they are nesting.'
Mr Cheung says Hong Kong is lucky in that, unlike many places around the world, not all of its beaches have been taken over by development. 'So if the turtles return, they still have somewhere to nest.'
But the presence of a nesting beach does not mean the end of all problems for a green sea turtle. Because it spends most of its life in the sea, a turtle is subjected to many of the threats facing other marine animals: sharks, disease, fishermen, hunters and, of course, pollution.
Paul Lam Kwan-sing, acting head of biology at City University, has been looking into the effects of marine pollution on green sea turtles. He has published two studies on the levels of chemical and heavy metal contaminants in the flesh of turtles and their eggs found in Hong Kong. Although he has detected measurable amounts of many toxic substances in both flesh and eggs, Professor Lam is cautious about what that means for the wider marine environment.
'I don't think the concentrations are alarmingly high,' he says. 'Because turtles have such a wide foraging range, what we are seeing is the general level of contaminants in the South China Sea. The readings are different to those from waterbirds, which feed along the coast [where the effects of civilisation are more acute].'
Professor Lam believes the level of toxic substances picked up by turtles, which breathe air, is also far less than fish because fish draw oxygen from the water, meaning toxins go directly into the blood stream. As their diet is primarily vegetarian, green sea turtles do not absorb as many toxins through their diet as, say, carnivorous dolphins.
'Despite this, we are still finding levels of some contaminants that could cause problems down the track.'
One of those substances is selenium, which is essential for many bodily functions but in large doses, has been linked to reproductive disorders.
In a paper published last year in the journal Environmental Pollution, Professor Lam and a team of other researchers wrote: 'Sea turtles have a long lifespan and high mobility, thereby increasing the chance of them being exposed to environmental toxicants.
'It is conceivable that certain environmental contaminants may accumulate in relatively large quantities in the bodies of sea turtles, consequently posing a health risk to these animals.'
However, he says there just isn't enough data available to determine what impact, if any, these pollutants are having on the life spans or reproductive health of the turtles.
Mr Cheung agrees that far more research needs to be done.
'According to the surveys and studies, the water quality off Tai Long Wan is actually not too bad ... and you do find some quite rare marine and benthic organisms there,' he says. 'But the problem with garbage is probably one of the bigger challenges to turtles.'
Mr Cheung says large build-ups of refuse, particularly big items such as refrigerators, could disrupt turtles' nesting habits by forcing them to bury their eggs closer to the water's edge. Their eggs need to be kept above the waterline while incubating to let the developing embryos respire.
The other major danger from rubbish is posed by drifting plastic bags, which to the eyes of an adult turtle resemble one of their favourite foods. And garbage poses a huge threat to freshly hatched turtles, whose mad scramble to the water's edge can be brought to a sudden halt by something as insignificant as a discarded soft-drink can.
'I think that is when garbage poses the biggest problem,' Mr Cheung says. Trapped turtle hatchlings are especially vulnerable to predators such as gulls or crabs and can also die of dehydration if they are unable to reach the water.
It was in the process of attacking the garbage problem that a group of campers came across the large female laying her eggs. The group was staying at Tai Long Wan to prepare for a beach cleaning event held as part of International Coastal Clean-up - a project aimed at raising awareness of the global threat posed by marine pollution.
Lisa Christensen, director of EcoVision Asia - which co-organises the Hong Kong clean-up event - and a friend were collecting firewood at about 9pm when they caught sight of the huge turtle, measuring about a metre across the shell, making her way up the beach from the sea to find a suitable nesting spot.
Keeping their distance, they watched as the turtle dug a 90cm-deep nest and proceeded to lay what looked like about 100 eggs over the course of three hours.
After the turtle had covered the nest and returned to the water, they marked the nest and returned to camp.
It was only after doing some research with a photographer friend, Paul Hilton, that Ms Christensen realised it was quite late in the season for the eggs and that human intervention might be required to improve their chances of survival.
It was then that they contacted the AFCD and came into contact with Mr Cheung, who has been involved in the department's turtle egg-incubation project for several years.
'We only recover the eggs if there is a need,' Mr Cheung explains.
'For instance, we would take the eggs if the nests were close to the water and vulnerable to flooding or if, in cases such as this, we were not sure if the impact of the number of visitors to the beach might pose a threat.'
The eggs must be harvested and transported so as not to disturb the embryos. This meant labelling each egg and placing it in a sand-filled bucket in exactly the same position as it was found.
AFCD officers then walked the eggs out of the remote beach rather than risk them being damaged by the pitching motion of the sea. Now they have hatched, Mr Cheung says they will be released at Tai Long Wan once the water has warmed up again.
'One of the theories of how they find their way back to their natal beaches is that they use chemical cues and rely on the smell of the beach,' he says.
'We even incubated them in sand taken from around the nest, because we are not sure at which stage they collect the scent.'
Late last year, two baby turtle carcasses were found at Tai Long Wan, raising the possibility that there was more than one nest and perhaps more than one nesting female.
'We will do a DNA test to see the genetic variation between those two and the hatchlings, as well as turtles from Sham Wan and the Huidong Gangkou Sea Turtle National Reserve' in Guangdong, Mr Cheung says.
Both he and Professor Lam say although there is doubt that South China Sea toxicants drastically affect turtles, that is no reason to ignore the issue of pollution or littering.
Ms Christensen, who regularly visits Tai Long Wan, agrees, noting that aside from sewage and industrial waste, the litter left behind by hikers and campers could pose a significant risk to Hong Kong's marine environment.
'Hopefully, this amazing discovery will help build awareness of the importance of conserving Hong Kong's beautiful coastlines and protecting the breeding grounds of this magnificent, but endangered, species,' she says.