Last stand of the Madagascan spider tortoise

Holding a spider tortoise

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The spider tortoise - one of the rarest tortoises in the world - is the equivalent of a microwave meal for the Mikea, a hardy Madagascan forest tribe.

The method is simple: bury tortoise in heated sand, wait 20 minutes, slurp superheated innards.

"It even comes in its own bowl," explains Solo, a seasoned tortoise hunter, although, he adds, "It's hard to get big or fat or full from eating such small animals."

Due to the Mikea and a slew of other threats, the spider tortoise is hurtling towards extinction. Could a newly identified population rescue them from the brink or are the odds against them too high?

Wildlife of Madagascar

Baobab trees

The island of Madagascar, off the southeastern coast of Africa, is home to a host of one-off animal and plant species found nowhere else in the world

Under a worst case scenario, scientists calculate that spider tortoises could disappear in a matter of a few decades: less than a single tortoise's lifespan.

As a result, in 2008 it was listed as critically endangered on the IUCN's Red List for Threatened Species.

Paltry to start, its range - a 555km long, 10km wide sliver of coast in southwest Madagascar - has shrunk by 71% in the last century. Just eight populations remain, with an average density of just over two tortoises per hectare.

Spider tortoise Shangri-La

But recent field-work suggests that there is a glimmer of hope. Biologists from the Open University, UK, the Madagascar Biodiversity Partnership and UK-based marine conservation NGO Blue Ventures, have identified a new population of spider tortoises where densities are the highest ever recorded for the species.

It is not only the last significant population of the northern subspecies, Pxyis arachnoides brygooi (the most threatened of the sub-species), but also of the species as a whole.

In January this year, 19.8 tortoises were recorded per hectare in this new population - almost 20 times the average density for the subspecies, and almost 10 times the average for the species as a whole.

Measuring a spider tortoise Shells are measured before being marked with nail polish

"What we've found is a spider tortoise Shangri-La, the last place on Earth where these tortoises could be as abundant as they were before humans started interfering," says Ryan Walker, a field biologist from the Open University.

Walker should know: he and his Malagasy colleague Tsilavo Rafeliarsoa from the Madagascar Biodiversity Partnership have spent the last three years systematically trawling the species' original range searching for remaining populations.

In 2010, a tortoise hunter tipped him off about an excellent hunting ground nearby. Walker and Rafeliarsoa asked NGO Blue Ventures, who have a permanent presence in the region, to survey five quadrats at the site every six weeks for a year.

Using conservation funds from the US-based Turtle Survival Alliance and Turtle Conservation Fund, surveyors were asked to record the sex, size and age of all tortoises found, and mark their shells with pink nail polish.

Tortoises were so abundant at the site that surveyors logged 99 in 50 man-hours across an area of just five hectares. That was roughly the same number that Walker and Rafeliarsoa found after spending 300 man-hours walking 130km between the Mangoky River in the north of the spider tortoise's range to near Lac Anony, its south west extremity.

Juveniles are unusually plentiful at the newly discovered site, comprising almost 60% of the population.

Start Quote

For these hunter-gatherers, who survive opportunistically on lemurs, fruit and wild honey, eating tortoises can be a difference between life and death”

End Quote Ryan Walker Open University

"This is really significant as juveniles are almost impossible to find elsewhere," says Walker explaining that the reason juveniles, and the species in general, thrive here is because local taboo or "fady" forbids their consumption.

Forbidden fauna

The villagers believe that eating spider tortoise will bring death, or at the very least some kind of slap on the wrist by their ancestors. The fady does not hold any sway over visitors, however.

Having wiped out the radiated tortoise - a footrest-size species with even poorer hunter-evasion skills - the wandering Mikea increasingly snack on spider tortoises, says Walker, who recently stumbled upon a pile of over 80 burnt carapaces in the area.

The Mikea continue to visit, even though the president of the village (an elderly man who volunteers as a surveyor for the research) has warned them they will be "beaten up" if they are found.

They are rarely found, however: the 2000-strong tribe is so elusive that, until recently, the Malagasy public believed it to be a fantasy akin to fairies or leprechauns.

Although the Mikea pose a serious threat to the tortoises, it is important to remember that the tribe are among the most impoverished people in the world, says Walker.

Koto a surveyor hold a tortoise Local villagers carry out the survey work

"For these hunter-gatherers, who survive opportunistically on lemurs, fruit and wild honey, eating tortoises can be a difference between life and death," he says.

But to satisfy their need for fuel wood, the Mikea are also behind another threat facing the spider tortoise: habitat loss.

The spiny forest of southwest Madagascar, home to baobabs covered in paisley-patterned fungus and giant pipe-cleaner-like plants, contains more endemic species of plant than any other ecosystem on the island.

95% of this flora is found nowhere else yet it is disappearing faster than Madagascar's rainforests.

A 2007 analysis of aerial footage by Conservation International estimated that up to half of the spiny forest disappeared between 1970 and 2000, with a further 51 to 80% lost in the past decade.

A recent analysis by Walker, Rafeliarsoa and colleagues from the University of Wollongong in Australia, has confirmed that the annual rate of forest loss in the last decade in some areas home to spider tortoises is 1.2%. That is roughly three times the average rate of forest loss across Africa as a whole.

Travelling tortoises

On the bright side, Walker's research suggests that spider tortoises may be more resilient to deforestation than previously thought.

It is widely believed that spider tortoises do not travel across large expanses of degraded land.

Spider tortoise facts

Spider tortoise
  • Spider tortoises are named for the golden "spider webs" that span their shells
  • They also have a unique anterior plastral ridge: a fleshy drawbridge that can be winched up after they have tucked in their heads and arms, allowing them to conserve water
  • They live in sandy soil where they will bury themselves during winter in order to stay warm

Yet almost a third of all of the tortoises recaptured during the study - a total of 57 individuals - were recaptured in different quadrats, all of which were separated by scrub.

Two particularly intrepid tortoises travelled almost 2km between quadrats; across a landscape stripped of trees, strewn with rubble fences and frequented by humans fetching water.

"Sadly we know nothing about the ranging patterns of spider tortoises and previous statements by scientists were probably just guesses," says Walker.

But he still believes that it is unlikely that tortoises at the site will travel far enough to encounter the next nearest population which lies roughly 40km away.

Also, the tortoises' problems do not stop at home. Armed poachers known as the "tortoise mafia" are targeting spider tortoises to cater to a growing appetite in Southeast Asia for unconventional pets.

International trade in the tortoise was banned in 2004 by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), but the mafia continues to smuggle them out of the country. Even high-ranking army officials have been caught sneaking tortoise stuffed suitcases onto military planes.

If the spider tortoise goes extinct, it will not be the first species of tortoise Madagascar has lost: the ancestors of the Mikea wiped out the island's only two species of giant tortoise.

But it is also unlikely to be the last. Madagascar's three other endemic species of tortoise; the flat tailed tortoise, the radiated tortoise and the ploughshare tortoise, are also listed as Critically Endangered.

Unexpectedly, extinction of the spider tortoise may even be triggered by fishing folk, who, struggling to catch enough fish on degraded reefs, turn to the species for food.

We encountered Tovo, who had failed to catch any fish that day, hunting for spider tortoises in one of the research quadrats last October.

"I can't go home with just my 10 fingers," he said.

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