Hawksbill Turtles, Seychelles
Since 2006 Rainer von Brandis has been studying hawksbill turtles at D'Arros Island in the Seychelles. He is working towards his Doctoral thesis focusing on the foraging habits of these turtles.
The ongoing research of Rainer von Brandis into the impacts of hawksbill turtle foraging behaviour in the Seychelles has been revealing the startling importance of their role in maintaining balanced coral reef ecosystems. With another season’s field work drawing to a close, it’s a good opportunity to reflect on Rainer’s discoveries thus far.
Hawksbill turtles have been severely depleted by humans in recent centuries and their absence from modern reefs has almost certainly influenced ecosystem dynamics. Prior to their depletion, hawksbill turtles had substantial influence on their marine habitats through their many roles as consumers, prey, and competitors; as hosts for parasites and pathogens; as substrates for epibionts; as nutrient transporters; and as modifiers of the landscape.
At D’Arros Island, Rainer’s underwater observations indicate that the roles of foraging hawksbills as both consumers and modifiers of the landscape are fundamental to the sustained functioning of the platform reef ecosystem.
Hawksbill turtle extracting a sponge from the reef. Photo by Rainer von Brandis.
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During the past two centuries, unregulated harvesting resulted in significant reductions of sea turtles in the Seychelles. However turtles have been under complete protection since 1994 and fecundity within the region has gradually begun to improve. Indeed, there is evidence that nesting hawksbill numbers are increasing in places where they have been protected over several decades (e.g. Cousine Island and Aldabra Atoll). Nevertheless climate change may threaten the future outlook for foraging hawksbills in Seychelles.
Climate change has resulted in increased mean sea surface temperatures, rising sea levels and changing weather patterns, all of which may have detrimental effects on shallow hawksbill foraging habitats. In contrast to other known threats to hawksbills such as poaching, pollution, physical anthropogenic destruction of habitat or incidental capture in fishing gear the effects of climate change cannot be managed or counteracted on site.
- Hawksbill turtle passing over a reef reduced to rubble. Photo by Rainer von Brandis.
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The fact that Rainer has managed to demonstrate that these marine reptilians play a pivotal role in maintaining coral reef biodiversity makes their fragile status of Critically Endangered all the more alarming. Under serious threat of extinction, the removal of these wardens from the reef could have even more dramatic knock-on effects throughout the ecosystem than previously thought: no longer being preyed upon by turtles, sponges could then out compete corals and dominate the reefs, causing reef ecosystems to support a far lower biodiversity.
Hawksbill turtles are in trouble because they have been harvested for thousands of years mainly for the aesthetic qualities of their shells, which are used to make combs, jewellery boxes, spectacle frames and ornaments. However, somewhat misleadingly, such products are usually referred to as ‘tortoise shell’ despite being produced from the scutes, or shell plates, of the turtles, making the true source of the product less apparent to customers. The exploitation of hawksbill turtles stretches back far through history: after invading Egypt Julius Caesar prized tortoise shell so highly he brought it back to Rome amongst his chief spoils; ninth century Arabs traded in tortoises hell throughout the Indian Ocean; and by 1700 Japanese artisans were carving exquisite ornaments from tortoise shell (called bekko) that were traded in markets around the world. Japan subsequently became the primary buyer of hawksbill turtles, with in excess of 1.3 million dead individuals being imported between 1950 and 1992.
Hawksbill turtle forages on a reef in the Seychelles. Photo by Rainer von Brandis.
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Over the past four years Rainer von Brandis has familiarised himself with a population of the usually timid hawksbill turtle in the Amirante Islands, Seychelles. This has allowed him to observe the turtles behaving naturally in their aquatic environment, revealing just how important they are for the maintenance of biodiversity on coral reefs.
The remote nature of Rainer’s study site, combined with a sound conservation policy in the Seychelles, means it supports relatively healthy turtle numbers. Consequently it has been possible to monitor how the hawksbill turtles function within a coral reef ecosystem outside of the relentless over-exploitation that has left them classified as Critically Endangered by the IUCN. Gradually, Rainer has been able to determine their prey preferences, how much they eat, their habitat requirements and even social interactions.
Reef fish lurk for scraps as a hawksbill turtle dines on sponge. (Photo: Rainer von Brandis)
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More so than you might think.
Amongst marine researchers, the critically endangered hawksbill turtle is notoriously difficult to study in its natural habitat. Like tortoises, turtles are often viewed as slow, lumbering reptiles, but any scuba diver fortunate enough to see one in the wild will appreciate that encounters tend to be fleeting. These skittish creatures are usually seen darting into the blue, wary of any unfamiliar presence. Hawksbill turtles are typically cautious of anything larger than themselves due to the associated risk of predation, hence their tendency to avoid people and the subsequent problems faced when trying to study them.
Although their reproductive cycle is reasonably well understood from being so accessible when tirelessly digging their nesting pits on the beach, the difficulty of locating hawksbill turtles underwater, and crucially being able to observe them for any length of time, has meant that their feeding methods, prey preferences, social interactions and impact on their environment all largely remain a mystery.
Once used to his presence, these hawksbill turtles treated Rainer like any other marine denizen.
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