Recovery plan for the Bramble Cay melomys (Melomys rubicola)

Executive summary

Species

Bramble Cay melomys, Melomys rubicola, a small rodent of uncertain origins, is morphologically distinct from other Australian melomys. With a population of less than 100 individuals inhabiting a single small sand cay whose existence is threatened by erosion, the Bramble Cay melomys is one of the most threatened mammals in Australia. Speculation exists that the species may also occur in Papua New Guinea (PNG) given the close proximity of the cay to the Fly River region, or on other islands in the Torres Strait. Further survey work on these islands and PNG along with clarification of its taxonomic status in relation to PNG species is required.

Current species status

The small population size and the naturally unstable nature of Bramble Cay has led to the species being listed as ‘Endangered’ under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and ‘Endangered’ under the Queensland Nature Conservation Act 1992 (NCA).

Habitat and distribution summary

Bramble Cay is a small (approximately 5ha), vegetated sand cay surrounded by reef and located in the far northeast of the Torres Strait, about 50km from the mouth of the Fly River in PNG. Vegetation consists of low herbaceous cover to about 40cm in height. It is intermittently broken by bare patches of compacted guano depressions that hold water during the wet season. Bramble Cay melomys appear to primarily inhabit the vegetated portion of the cay, an area of about 2.2ha. Eleven plant species have been recorded however composition varies from year to year. Bramble Cay is also the largest nesting site of green turtles in the Torres Strait and supports the only large seabird colony in the region.

Threats summary

1. Erosion of the cay is the major threat to the species survival. The cay is in a state of flux with its movements strongly influenced by the prevailing weather patterns. While there appears to have been a net loss of the cay in recorded history, recent measurements suggest the cay might be in a depositional phase. Erosion may be compounded by high winds, wave action and storm surges associated with cyclones.
2. The introduction of exotic predators or weeds to the cay could potentially be catastrophic, given the small and vulnerable nature of the melomys population. The cay’s isolation, close proximity to PNG and its use as an anchorage by fishing boats means there is a threat of pest and/or disease establishment. Two weed species are already present.
3. Genetic analysis of this species reveals a level of inbreeding which theoretically could lead to inbreeding depression and ultimately extinction.

Recovery objective

The overall objective of this recovery plan is to secure and enhance the status of the Bramble Cay melomys through an integrated program of monitoring, on ground management, searches for other populations and raising public awareness.

Summary of actions

To meet the overall objective for the Bramble Cay melomys recovery program, the following actions are required: establish monitoring programs to assess population trends, habitat condition and cay movement, and to detect and respond to the presence of invasive species; conduct field surveys to locate additional populations; undertake research to clarify Bramble Cay melomys taxonomy and improve knowledge of the species ecology; facilitate community involvement in and encourage support for Bramble Cay melomys recovery by engaging Indigenous groups and promoting the species to the Torres Strait and wider Australian communities; and ensure effective management of the recovery program by facilitating stakeholder involvement in the implementation of the recovery plan and establishing data sharing arrangements between Erubam Le and the EPA.