Editor, Earth News
An adult spider tortoise can fit on one hand
Poachers are threatening the survival of the northern Madagascar spider tortoise, which only lives along a narrow strip of the island's coast.
The animal has disappeared from swathes of its habitat, taken by collectors to supply the exotic pet trade.
Wild numbers of the tortoise may have already fallen by 90%, say scientists who have just surveyed its population.
The problem continues to worsen due to political instability in the country, which makes it easier for smugglers.
The Madagascar spider tortoise is one of the smaller species of tortoise, and is distinguished by the intricate spider web patterning on the shells of adults. Hence its scientific name Pyxis arachnoides.
It occurs as three distinct subspecies, each of which has a slightly different shell shape and lives in a different part of the coastal spiny forests within southwest Madagascar.
Prime tortoise habitat: boab trees in the Mikea forest of Madagascar
However, the tortoise's appearance is also its downfall.
A new survey suggests that the northern Madagascar spiny tortoise (P. a. brygooi) is now extinct across 50% of its former historical range, with huge numbers being collected to supply the international trade in exotic pets.
Trade in the species is banned, but thousands of the animals are still being smuggled out of the country illegally, says Ryan Walker, a senior wildlife biologist at Nautilus Ecology based in Greetham, Rutland, UK.
Walker, who is also a member of the International Union for the Conservation of Nature's (IUCN) Tortoise and Freshwater Turtle Specialist Group, conducted a survey in March covering all the whole range where the tortoise was once thought to live.
Together with biologists from the Open University in the UK, the IUCN specialist group and the University of Antananarivo in Madagascar, Walker searched 60 sites in detail for wild spider tortoises, recording their occurrence and population density.
He presented the results this month to the Turtle Survival Alliance Meeting in St Louis, US and is also submitting them to the journal Herpetologica.
SPIDER TORTOISE SUBSPECIES
The northern subspecies has a ridged plastral lobe, the hinge at the front of the tortoise's shell under and into which it can tuck its head and front legs. It lives up to 10km inland along a narrow 600km strip of coastline.
The mid subspecies lives further south, separated by river systems, and has a semi-ridged pastral lobe.
The southern sub species has a completely mobile lobe, allowing the animal to retract its head and limbs and then close up the flap at the front, an adaptation that may help it conserve water in its drier southerly habitat.
"The most striking aspect of the survey was that huge areas of suitable habitat were completely devoid of tortoises. A sure sign that the collectors had been in to collect them for either local consumption as food or collection for black market to supply the pet trade," says Walker.
He estimates that two million wild northern spider tortoises remain.
"That sounds quite a lot. But 35% occur in a very small area of forest and are susceptible to being wiped out pretty quickly by collectors."
"The remaining animals are in very isolated and fragmented populations with very low numbers of tortoises, which are unlikely to recover into healthy populations," Walker says.
"As an educated and conservative guess I would say that the global population of northern tortoises have probably decreased by greater than 90% since human induced pressure has been placed on the animals."
Some local communities hunt the tortoise for food. But the greatest threat comes from organised gangs visiting the area and collecting spider tortoises for illegal export.
A single spider tortoise can reach US$1000 each on the pet and exotic reptile market, prices that drive the unsustainable trade.
The northern subspecies is probably facing greater threats than the other two subspecies from poaching, by local populations as a food source and also by gangs for export to support the illegal pet trade in the animal.
Measuring a juvenile
The other two subspecies don't tend to end up as readily on the pet market and the tribes further south won't eat them, however they are suffering from an alarming rate of habitat destruction, says Walker.
He also says the threat to the tortoises from poaching is currently greater due to the current political turmoil in Madagascar brought about by the political coup in January.
Disorganisation at government level has meant that it is easier to get endangered species out of the country with false paperwork or blank permits that are easier to get hold of, he explains.