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Hawksbill Turtle: The Sponge Eaters

With a beak like a hawk and a carapace design more majestic than any human art, the Hawksbill turtle (Eretmochelys imbricate) is perhaps the most beautiful of all the sea turtles. It is easy to lose yourself when swimming above these magnificent turtles as they search the reef for sponges to eat. What they lack in size is easily made up for in aesthetic splendour.

Hawksbills are distributed worldwide in tropical and subtropical coastal waters, living in the waters of 82 nations and nesting on beaches of 60 of these. They migrate hundreds of miles between feeding grounds and nesting grounds even if there are suitable feeding and nesting grounds right next to each other. The drive to return to natal nesting beaches is strong. Unfortunately, today’s hawksbill population represents less than 10% of what it was just a century ago.

Once nesting in colonies, the hawksbill is now a lone nester. You can easily distinguish hawksbill landing tracks from that of the green due to its alternating style of locomotion. Once in nesting season females lay 3-5 clutches at an interval of 13-16 days in a single season, laying an average of 130 eggs. Hawksbills have a natural hatchling success of around 80-90%, however some beaches have high predation rates and in the Caribbean suffer from hurricanes.

Following on, once the turtles have hatched they spend the first 1-3 years at sea often living in floating rafts of sargassum. Not until they reach a certain size will they return to coastal waters and start living on a diet of sponges. They will stay in these feeding grounds waiting to become sexual mature at around 20-25 years. Hawksbills evolved their sharp pointy beak to allow them to pick sponges out of cracks and crevices in coral reefs and bite off pieces of sponge from mangrove roots.

When we think of a sponge we think of a soft object used to wash dishes. However, a living sponge is one of the most primitive multicellular animals on earth. Their skeletons are made of spines composed of calcium, silica or protein depending on the species of sponge. Scientists did not know what hawksbills were eating until researcher Anne Meglan examined the stomach contents of a dead hawksbill. One of the spikes from the sponge got stuck into her finger and after a few years this led to her losing her hand due to a tumour that developed around the toxic spine. This did not deter Anne and she continued to become one of the head scientists when it comes to hawksbill conservation, however the question remains, how do the hawksbills stomachs deal with such a dangerous food source?

Eating glass-like spines with toxic chemical compounds would kill a human, even local humans on coral reefs will not eat hawksbills due to the toxins in their meat. The hawksbills require some time for their physiology and digestive tracts to adjust to such a diet. Eating such a diet does mean that hawksbill’s have a completely exclusive diet and face no competition for their sponge banquets.

This peculiar diet plays a vital ecological role in the creation of diverse reef environments. Too many non-coral animals and plants such as sponges can end up growing on coral reefs and choking out the coral by blocking the sun. Sponges are one of the main competitors for space on the reef. So hawksbills predating on these sponges play an important role in allowing the coral to flourish. An average hawksbill (70kg) eats and average 544kg of sponges a year. 200 years ago there were some 540,000 adult hawksbill in the Caribbean, eating 294 million kg of sponges each year. Hawksbills are truly the architects of the reefs, controlling the numbers and size of sponges, allowing the corals to grow. A reduction in hawksbill populations is starting to lead to sponges taking up about 12% of reefs in Puerto Rico and accounting for 70% of coral overgrowths on Florida reefs, emphasising the importance of maintaining a healthy, whole ecosystem.

Following on, hawksbills are currently listed as critically endangered by the IUCN. Current population estimates suggest there are around 60,000 hawksbills left, just a fraction of their previous populations. The main reason for these population crashes are from over-exploitation. Its scutes have been made into jewels by Egyptians, Romans, Chinese, Europeans, Arabs, American Indians and Japanese. Used to inlay antique furniture, combs fans and other ornaments.

While the scutes are definitely more beautiful than their plastic replacements, the beauty is the reason the hawksbill has been hunted close to extinction. Not surprising when looking at trading figures. Indonesia exported more than 700,000 juvenile and adult hawksbills between 1970-1986. In some places like Madagascar populations fell so low by 1973 there was not enough turtles left to support a trade any more.

The trade in tortoiseshell is now banned by international treaty, greatly reducing the marketplace for it. However, many countries are still heavily engrossed in the illegal sale of hawksbill shell. Hawksbills are still being slaughtered in Indonesia and most eggs are taken in Malaysia to be legally sold on the market.

Despite this, things are not completely gloomy. With a continued ban on international trade, more ecotourism and increased education and enforcement, there is hope that numbers can rebound. Most nations have enacted laws to protect hawksbills and international trade is slowing as the amount of protected beaches are increasing.

The beauty of a hawksbill is much better off left in the ocean. In fact hawksbills have an estimated worth of $30,000 each to a local resorts economy. If we can show local government officials and villages that they don’t need to kill the animal to make money from it, then maybe we can change the tide. The mind set of seeing these turtles as an endless commodity must be changed, you cannot continually harvest the eggs of turtles and later question why there are less mother’s returning to the beach.

We have a duty to protect the species that share this planet with us, especially when it is human impact that has caused such rapid population declines. Saving the hawksbill turtle will not just help the species itself but will conserve its important ecological role. Hawksbills are the maintenance keepers of the coral reefs, if we lose them we could have a cascading case of destruction to our reef ecosystems. We must help hawksbills to help our reefs. When locals can be shown they are worth more alive than dead, then protection may improve.

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