Rats run riot!
When making our blog entries we are always on the "look out" for interesting and unusual satellite applications. Well, this week we have something "completely different"! Eagle Island, in the Chagos Archipelago, is overrun by rats! And it's all thanks to the human population that inhabited the island until 1935. Before that coconuts where farmed to provide oil, principally for lamps, but with electricity becoming widely available the economics of transporting the commodity from Eagle Island just didn't stack up. So the Island was left to return to nature - the problem was the rats stayed and truly made the island their home!
Now Eagle Island, at 5 x 0.5 km is the second largest in the archipelago after Diego Garcia and the only island in the Great Chagos Bank to be infested by the Black Rat (other rat-infested islands occur in other island groups of the archipelago, and Diego Garcia is also heavily infested). Our friends the rats are seemingly preventing the breeding of seabirds which on other islands within the group are prolific, providing some of the most valuable seabird breeding areas in the entire Indian Ocean despite the tiny sizes of these islands. The rats were also maintaining a less than desirable vegetation state by preventing the regeneration of indigenous species and by feeding on the eggs and hatchlings of nesting marine turtles. There are no land birds on the island, probably in large part due to the rat presence. Anyway, that's all changing now and we can measure this by using satellite imagery.
So how were the rats controlled? Firstly a baiting grid 30 x 30m was established across the entire island based on lines cut by hand through the dense vegetation by the eleven expedition members over a 6 week period during April this year. These provided an excellent opportunity to conduct a Rapid Assessment Survey of the state of the environment of the entire island surface using the resulting 2,844 grid points as recording stations. Ten parameters including the type of vegetation were recorded at each station by four expedition members. This data is now being mapped and together with other expedition results will be the subject of a "state of the environment" report later in the year.
Satellite imagery has been difficult to come by, not least because there is seemingly little of general interest to the world on tiny uninhabited islands in the middle of the Indian Ocean. As the result satellites are rarely focused - if at all - on the island, and any resulting images are almost unobtainable. The CHRIS images from the Surrey Space Centre will accurately compare images taken in April this year with those due to be taken in October. The CHRIS images will also high quality maps for conservation management purposes.
Results of the assessments will be used in assisting future management processes in this far-flung location, part of the British Indian Ocean Territory (BIOT), not least in monitoring the effects of the rat eradication and any other interventions to be made in future conservation.
So it's bad news for the rats but good news for the Island's environment and sea bird colonies.
