Climate Change And How It Is Going To Affect

The Aldabra Giant Tortoise

 

 

   The Aldabra Atoll is a secluded place, with a coral reef helping to protect it from easy access by plunderers of yesteryear. This is one of the main reasons why man never managed to completely wipe out this species of giant tortoise, unlike the other 9 species who were not so lucky.

 

   Nowadays, since the 1980’s, the Atoll is heavily protected by legislation and only the luckiest of scientists are even able to set foot upon its shores, with visitors kept to a bare minimum. However, mans dire influence on the rest of the world is just as likely to cause this species irreparable harm, without invading the island.

 

   Unfortunately Aldabra is located near to one of the busiest shipping routes on the planet, it would be ever so easy for there to be an oil spill and cause a cataclysmic contamination to the whole area, and potentially wiping out a delicate ecosystem.

 

   The wild population of Aldabra tortoises numbers around the 150,000 mark and it is able to self sustain itself. They have not really evolved in their design since prehistoric times, if it works for them why change it seems to be their policy, unfortunately this means they are not going to change quickly enough to combat the accelerating effects of climate change.

 

   Although these animals are reptiles and they like and need warm weather to survive, the rate that temperatures are rising could also be what finally kills them off for many reasons.

 

   Firstly Aldabra is an Atoll in the middle of the Indian Ocean. We know that the polar ice caps are melting and this means that gallons and gallons of water are being added to the worlds seas. This means sea levels are on the rise around the planet.

Direct Effects Of A Rise In Sea Levels On Aldabra.

· There will be less land rising up above the sea, so less space for the animals to live.

· Less space puts more pressure on the food available, they will eat it more quickly and spend longer starving, which will make the tortoises be in poorer condition.

· Poorer condition adults leads to poorer conditioned babies and potentially reduced clutch sizes.

· Aldabra is a Volcanic Island and it is very difficult to find anywhere they are able to dig deep enough holes to lay their eggs, so they use the beaches. However, with rising water levels the beaches will be the first to be submerged, leaving them struggling to find somewhere to safely put their eggs.

· If they do manage to lay them on the beach, there is a greater risk of them being washed away by the tide or them being covered over with water for longer killing the hatchlings or cooling the temperature around them so they don’t even begin to grow.

· The Atoll is actually made up of 4 Islands with a tidal lagoon in the middle. Rising water will mean this tide probably will not go out, fully, each day which will cut off the 4 islands from each other and thus severely limiting the range that an animal can travel searching for both food and mates. If the population is separated and isolated from each other, in this way, then you will get inbreeding, which will weaken the species.

 

Direct Effects Of Higher Temperatures On Aldabra.

· These tortoises lay their eggs in the ground and the ground temperature incubates them to become hatchlings. However, higher temperature rates will probably mean greater numbers of clutches failing to hatch. At temperatures over 34C the risk of mortality or deformity amongst the young is significantly higher.

· Another issue with higher ground temperature will mean that the soil and sand above them dries out and becomes much harder. This 5 cm hatchling has to dig its way to the surface, once it has escaped the egg, it can take it days or even weeks to achieve this feat. If the ground is harder then they are going to struggle to get through the substrate above the eggs and may well die from exhaustion or starvation or lack of air, before they have even exposed their first toe nail to the world.

· Tortoise eggs are subject to something called ESD or Environmental Sex Determination, to give it the full title. This means that the temperature the eggs are incubated at has a direct effect on the sex of the hatchlings. Higher temperatures will definitely create a bias towards one sex, we know that higher incubation temperature generally produces more girls. This means there is going to be an abundance of females and a shortage of males in the wild population. Again, over the long term, you are going to be risking in breeding.

· Drier, hotter, weather means less rainfall. The tortoises are surrounded by sea water but they only get freshwater to drink when it rains, which is why they are forced to fast for several months of the year, already. An increase in temperature will make these wet seasons even further apart and possibly of shorter in duration. Lack of water throughout the year, for the tortoises, is going to lead to kidney and other health issues.

· Drier, hotter, weather also means the foliage growing on the Island will burn off quicker too, leaving less food available and less places to find it.

· It will also have the knock on effect that the species who pollinate the foliage that the tortoise eat will suffer too, meaning less pollination occurs and again causing a shortage of food.

· The lack of foliage and natural shrubs and bushes to shelter beneath will also cause the animals to overheat. Yes they are a reptile and need the sun to heat them up to temperature, but they also need the shade to cool themselves down too, as they can’t sweat and like us, anything over 30C, for long periods, can be too much for them.

· Natural evolution will ensure only the strongest survive, so the numbers in the wild population will begin to fall, and again, this is going to limit the gene pool that they have available.

 

Other Weather Issues

   If something like a Tsunami developed, in that region, then it could wipe out the whole island population in one go, Aldabra Atoll is only a few metres above sea level now, it would not take much to wash them all into the sea, killing most of the tortoises in the process.

 

   History and science has shown that over the millennia theses islands have been severely affected by weather and populations have been decimated, it has happened in the past and there is no doubt it will happen again, sometime in the future too. It is just a question of when and are we mobilised enough to help them repopulate.

 

   Man has caused these problems, for this peaceful animal, and it will be down to man to help save them. There are breeding populations in the USA and they are a popular pet around the world but they would need our animals in Europe and the UK to provide different blood lines.

 

   No one in the UK or Europe has successfully hatched Aldabra eggs, for many different reasons. One of them being, that Aldabras do not seem to be in any hurry to breed and many of the animals in the UK are too young to breed yet anyway. Now is the time when we can rally together and start thinking of ways we can make it a success despite the obstacles the UK environment throws up.

 

   With this in mind, we are hoping to work with other Aldabra keepers and owners in the UK to set up a UK breeding program, in the future.