Shark Bay mouse  (Pseudomys fieldi)

Before translocations to other locations began in 1993, the Shark Bay mouse was amongst the most threatened of all Australia’s mammals, being geographically restricted to just one small island, after having become extinct on the mainland. The precise reasons for the decline of this species are unknown, although a number of theories exist. One suggestion is that cats introduced to the mainland by 19th century may have been responsible for the decline and extinction of many native species on the mainland, but particularly rodents. Predation by foxes may also have had an impact. Another idea is that grazing and trampling by domestic stock brought over by European settlers has contributed to the extinction of Australian fauna on the mainland, possibly including the Shark bay mouse. Likewise, it has been proposed that the rabbit has degraded and competed for fertile habitat, a particularly scarce resource in arid zones of Australia, especially in those that experience successive periods of drought. Altered fire regimes have also been cited as a possible reason for the decline of native species. Sadly, the fact that the Shark Bay mouse does not construct substantial burrow systems underground, but rather build tunnels in vegetation, means that it is particularly exposed and vulnerable to these threats, more so than many other rodents (3).

Thankfully, the Shark Bay mouse population on Bernier Island is protected from the threats that have impacted those on the mainland, as this island is part of the Bernier and Dorre Islands Nature Reserve and lacks any exotic predators. Feral goats were eradicated in 1984, and public access is limited to day visits. Nevertheless, this restricted distribution left the species in a highly vulnerable position. Thus, a Recovery Plan was created for the mouse, which involved the translocation of populations to three other exotic predator-free island nature reserves, Doole Island (June 1993), North West Island (June 1999), and Faure Island (June 2003), and to Heirisson Prong, Shark Bay, on the mainland (November 1994), after intensive feral animal control had been undertaken (3) (5). The reintroduced populations have been monitored on an ongoing basis and restocking has occurred where necessary (3). However, the populations on Doole Island and Heirisson Prong have not persisted. It is believed that predation by Varanus lizards prevented the establishment of a viable population at these sites (5). To aid the translocation programs, a captive breeding programme was established in 1998 at Perth Zoo. It is vital that translocated populations become established and self-sustaining if this geographically restricted mouse is to be brought out of the danger zone, but so far these have had mixed success, and the future of this tiny mammal remains uncertain (3).