Re-introduction and conservation introductions of the western swamp tortoise in south-western Western Australia

Summary

The western swamp tortoise (Pseudemydura umbrina), Critically Endangered and restricted to a narrow, largely cleared strip of Western Australia's Swan Coastal Plain, nearly disappeared from its Twin Swamps Nature Reserve population after fox predation, a drying climate, and wildfire, prompting captive breeding at Perth Zoo since 1988 and juvenile re-introduction since 1994. The Western Australian Department of Environment and Conservation aimed to establish at least three wild populations totaling more than 50 mature individuals, since only the Ellen Brook population remained naturally. At Twin Swamps, a fox-proof fence, fox baiting, supplemental water bores, and prescribed burning supported the release of 162 captive-bred juveniles since 1994, with ultrasound scanning confirming egg production every year since 2002, though juvenile recruitment remains unconfirmed. At Mogumber Nature Reserve, historically suggested habitat acquired by the state in 2000, monthly fox baiting accompanied the release of 151 juveniles, reaching 45 known-alive individuals including three adults by 2007, exceeding its 35-tortoise target. At Moore River Nature Reserve, habitat modification through swamp bunding extended water retention enough to support a trial release of ten radio-tracked juveniles in August 2007, which showed normal growth rates after ten weeks. Perth Zoo maintained 25 breeding adults, well above the target of 12, producing 35 released juveniles in 2007 alone. The project rated itself Successful, having met four of five formal success indicators, with the fifth, an adult wild population exceeding 50, considered likely once better population estimates become available.