SPECIAL REPORT: Hawksbill turtles - keepers of the coral

Posted: 13 February 2010

Timid and difficult to locate underwater, hawksbill sea turtles in their marine habitat have long managed to evade the efforts of researchers. But Rainer von Brandis struck it lucky when he found himself swimming among hawksbills in the Amirante Islands of Seychelles, and his subsequent study revealed that these graceful reptiles are vital to the maintenance of coral reef biodiversity.

TEXT AND PHOTOGRAPHS BY RAINER VON BRANDIS

Better known for the aesthetic qualities of its shell than for the role it plays in maintaining coral reef ecosystems, the hawksbill sea turtle is classified as Critically Endangered by the IUCN. In view of this status, hawksbills have been the focus of numerous research projects in recent years, and while much has been learned about them when nesting, studying them in their aquatic environment has proven far more challenging.

Sea turtles underwater are difficult to locate and extremely wary, and often the only reward for researchers is a glimpse of one swimming off into the blue. Their natural behaviour, feeding methods, prey preferences, social interactions and impact on their environment are therefore still largely a mystery.

Seychelles, with its sound conservation policies, supports relatively healthy turtle numbers, especially at remote locations that were not frequented by turtle fishermen in the past. During an extended visit to the Amirante Islands in 2006, I came across a small insular coral reef that seemed to be teeming with young hawksbills. After diving around the reef for a few days, I soon realised that I was seeing the same turtles over and over again and that they appeared to be getting used to my presence. At first I was careful to keep my distance, but gradually they allowed me to approach to within arm's length and spend entire dives with them.

Hawksbill turtle
Hawksbill turtle
Hawksbill turtle.
The hawksbills, I decided, would be an excellent subject for my planned doctoral thesis, and for the next two months I spent as much time observing them as my dive computer allowed. The preliminary results were exciting and unique, and I consequently secured funding to return to the reef for two-month periods in 2007, 2008 and 2009. Each year I found the same individuals and they continued to allow me to follow them around.

Over the four-year period, I clocked up a total of 312 hours underwater with the turtles and identified 15 resident individuals. Eighty per cent of my time, however, was spent with the three turtles that had become most accustomed to me. Other than occasionally sitting on me, trying to eat my dive equipment or using me as leverage when digging for food, these three completely ignored me as they went about their everyday business. Naturally, I remained careful never to touch them or disturb them unnecessarily, as this would undoubtedly have changed their behaviour toward me.

Among other things, I was able to determine their prey preferences, the quantity of food they consumed, and their diving and activity patterns, social interactions and habitat requirements. Most significantly, however, I established that the hawksbills play a vital role in maintaining the biodiversity of the coral reef I was working on.

Hawksbill turtle feeding head down
Hawksbill turtle feeding head down
Feeding head down helps the turtle to probe tight crevices with its beak and break off stubborn pieces of the reef.
Because hawksbill foraging pressure is high on this small reef, the sponges they eat are restricted to well-hidden locations inside the reef substrate. The turtles therefore have to dig them out by using either their flippers to rip open the substrate or their beaks to pry the reef apart and lift out loose pieces that may be sheltering their prey. In doing so, they not only shape the reef topographically, but also expose food for fishes and create sheltered micro-habitats for other reef-dwellers such as moray eels, brittle stars, shrimps and a range of invertebrates.

Moreover, since sponges usually out-compete hard corals for space, the consumption of a quarter of a tonne of sponge by a single turtle each year enables hard corals to become established. This is especially important because higher than usual sea-water temperatures in 1998 resulted in the death of approximately 90 per cent of hard-coral communities in the region. If hawksbills had not been present, the reef would probably resemble a featureless expanse of mainly sponges and support a much lower diversity of reef organisms. In all likelihood, many coral reefs were more spectacular in the days preceding the mass slaughter of hawksbills for tortoiseshell.

Hawksbill turtle feeding on reef
Hawksbill turtle feeding on reef
On the reefs around the Amirante Islands, hawksbill turtles feed mainly on two species of sponge. Both are toxic to humans, and their skeletons consist of millions of tiny spines.
It is hoped that the results of this research can be used to improve the hawksbill's conservation status and strengthen resolve against a potential renewal of the tortoiseshell trade. Japan continues to lobby in support of reopening the trade so as to keep its tortoiseshell-manufacturing industry alive, and recent reports indicate that clandestine dealings in some Asian and Central American countries are on the increase again. In addition, the findings provide important information about hawksbill biology and habitat requirements, which is vital for the effective management of their populations and foraging habitats.

The author would like to thank the Save Our Seas Foundation for funding his research in the Seychelles.

This article first appeared in the December 09/January 10 issue of Africa Geographic magazine and is reproduced here by special arrangement.

TURTLE SCUTE TO TORTOISESHELL BANGLE

Tortoiseshell - used to make combs, jewellery boxes and spectacle rims - is a misnomer, for it comes not from tortoises, but from the hawksbill sea turtle. Produced from the scutes (shell plates) of the turtles, it has been considered a valuable commodity since ancient times. More than 2000 years ago Julius Caesar considered tortoiseshell to be one of the chief spoils of his triumph in Egypt, and in the 9th century Arabs traded tortoiseshell around the Indian Ocean.

By 1700, Japanese artisans were producing large amounts of beautifully crafted tortoiseshell ornaments (called bekko) for markets in Asia, America and Europe. Japan subsequently became the major importer of hawksbills: between 1950 and 1992 more than 1.3 million dead turtles were brought into the country.

Overexploitation led to the prohibition of trade in hawksbills in 1977, when the species made it onto Appendix 1 of CITES, but intercepted bekko shipments indicate that the industry persists and is fed by poaching. On a positive note, countries such as Seychelles and Tanzania have shown their commitment to ending the illicit trade by burning all their accumulated stocks of tortoiseshell.

YOU CAN HELP BY

Not buying tortoiseshell products

Hand-crafted tortoiseshell jewellery and ornaments, and even stuffed juvenile hawksbills, are often found at tourist markets in tropical countries. If you are really tempted to buy, check with the vendor that the item is made of 'faux tortoiseshell' (plastic) and not the real thing. Reporting poaching incidents

If you encounter a poacher who tries to sell you a live hawksbill (or any other sea turtle), it is usually best to decline politely and report the incident to the authorities immediately. With luck, the poacher will not have killed the turtle before being apprehended and it can be released. Purchasing turtles from poachers is not recommended because this will encourage them to catch more.

Any dead turtles found on a beach should also be reported. They probably died from being entangled in fishing gear and it is helpful to the authorities if such deaths are documented.

FAST FACTS

Hawksbill sea turtle (Eretmochelys imbricata)

Description. These medium-sized sea turtles attain about one metre in length and 80 kilograms in weight. An elongated and pointed beak and a serrated rear margin of the carapace are distinguishing features.

Range Circumtropical.

Habitat Usually coral reefs, but they also live in a wide range of habitats, including mangrove swamps, seagrass beds and mudflats.

Biology Three distinct life stages: hatchlings float on open ocean currents, feeding on various drifting organisms; at 30 centimetres (5-10 years old) they move into shallower reef environments and begin feeding on sponges and other invertebrates; at about 70 centimetres (25-35 years old) they become adults and return to their place of birth to breed. On average, females nest every third year and lay up to five clutches of 140 eggs per season. Out of a thousand eggs, only one or two hatchlings make it to adulthood.

Conservation Critically Endangered (IUCN Red List). As in other sea turtle species, their late age at sexual maturity and relatively low reproductive rate make them highly susceptible to overexploitation. Females lucky enough to reach adulthood are easily killed by humans for food or tortoiseshell when they come ashore to nest, while their eggs, a rich source of protein, are often harvested in totality. Relatively new threats such as pollution, habitat destruction, hybridisation and incidental capture by fishing vessels further reduce the outlook for this species.