The Bramble Cay Melomys (Melomys rubicola) had one of the most unusual and precarious distributions of all Australian mammals. As far as we know, the only place it occurred was a tiny 4-5 hectare coral cay in the eastern Torres Strait, off the tip of northern Australia.
Just how the species became isolated on such a remote coral cay remains a mystery. Given its close relatedness to Australian melomys, it’s been suggested it is a result of stranding by rising sea levels as ice melted following the Last Glacial Maximum. Surveys of adjacent inhabited Torres Strait islands have failed to detect Bramble Cay melomys, instead finding that the grassland melomys (Melomys burtoni) is a much more widespread species in the region.
The remoteness of the cay, has meant that research targeted toward Bramble Cay melomys has been very limited. However, the few surveys and anecdotal reports that could be gathered suggested it was a species in decline. In an effort to prevent its loss from the cay, a recovery plan was prepared in 2008. The main recommendations of this plan were:
- Establish a Bramble Cay melomys monitoring program;
- Clarify the extent of and manage threats to the Bramble Cay melomys;
- Clarify taxonomy of Bramble Cay melomys in relation to PNG species;
- Facilitate community participation and education in Bramble Cay melomys recovery; and
- Manage the recovery program.
As far as we can tell, none of these recommendations were acted upon. It was not until 2011 that our research group (care of assistance from TSRA) was able to visit the cay specifically to provide an update on the status of Melomys rubicola. By this time it seems it was too late. The survey then, and on another two subsequent visits to the cay have failed to detect any sign of the melomys.
Given the small size of the cay and lack of vegetation, from this we can confidently affirm that Bramble Cay melomys is extinct from the only known part of its distribution.It appears that the extinction was caused by a combination of rising sea levels and storm surge events. Extinction of Bramble Cay melomys may therefore be the first mammal extinction caused by climate change.
In the Torres Strait, sea levels (measured at Goods Island) have been steadily rising over the past 15 years (Figure A below).
In 2009 the rising seas were punctuated by a significant storm surge event that pushed sea levels up to 0.94 metres above predicted levels (Figure B).
Inundation of the cay by high sea levels likely had dire consequences for cay’s vegetation, and in turn the melomys. Comparisons of historical photographs show that there has been significant decline in the extent and quality of vegetation on the island – the melomys’ only food source. Debris found spread across the island provide evidence this vegetation decline has been the result of inundation by salt water.
There will be many that will argue the investment required to save this species from its apparent extinction is better spent on other species. Melomys rubicola was restricted to a single cay and was therefore unlikely to have major importance for the functioning of ecosystems or the survival of other species. However, given our country already holds the world’s worst extinction record for mammals – do we really have the right to pick and choose which of the remaining species we conserve?