Individual study: Effects of release method on the reintroduction success of banded hare-wallabies Lagostrophus fasciatus, Peron Peninsula, Western Australia
Hardman B. & Moro D. (2006) Optimising reintroduction success by delayed dispersal: is the release protocol important for hare-wallabies. Biological Conservation, 128, 403-411
Many Australian mammal species, particularly on the mainland, are highly threatened. Often there are sources of founder individuals for programs to reintroduce extirpated mammals to parts of their former range from captive sources or offshore islands. However, many reintroduction attempts have not considered different types of release methods, and thus, do not allow conservation managers to base decisions or actions on evidence of best practise. In this study, the relative advantage of acclimatising banded hare-wallabies Lagostrophus fasciatus through a soft-release protocol was investigated.
Study site: The study was conducted on the semi-arid Peron Peninsula, Shark Bay in Western Australia. The site is comprised predominantly of wattle Acacia sp. and patches of spinifex grass Triodia sp. Sheep and cattle have been removed from the area and are currently excluded by an electric fence. Red fox Vulpes vulpes have been eradicated from the peninsula and numbers of feral cats Felis catus and goats Capra hircus have been significantly reduced.
Study species: The banded hare-wallaby (or merrnine) Lagostrophus fasciatus , is restricted to Bernier and Dorre Islands in Shark Bay, Western Australia, where they number around 10,000 individuals. It is currently classified as vulnerable by the IUCN. They once alos persisted on the mainland of Western Australia but were extirpated by a combination of introduced mammals (both predators and herbivore competitors), habitat loss and changes in the fire-regime of the area. All of the hare-wallabies used in this study originated from an the population on Bernier Island, after which they were moved to a captive breeding centre on the Peron Peninsula.
Release protocol: Two release protocols were adopted:
1) A 'soft' release protocol whereby wallabies where introduced into a 3-ha enclosure surrounded by a predator exclusion fence for 14 days prior to release.
2) A 'hard' release protocol whereby wallabies were released directly into the wild.
Both release groups comprised six males and three females, and were given supplementary food consisting of kangaroo pellets, lucerne Medicago sativa and water, as required. Prior to release, all individuals were weighed and body measurements taken to enable calculation of a body condition index. Mortality-sensing radio transmitter collars (which transmit an accelerated signal after a period of inactivity) were fitted to each animal. During these procedures, wallabies were not anaesthetised, but were restrained, because they are relatively resilient to capture-related stress. Hard release individuals were released at the same time as the soft rlease enclosures were opened in 2001.
Post-release monitoring: All wallabies were located once per day using radio telemetry and their locations mapped. Individuals whose radio-collars emitted mortality signals were located, mortality verified and, if dead, the location of carcasses recorded. 30 Bromilow traps baited with fresh fruit and set within a 1 km distance of known locations in a linear arrangement along roads at 100 m intervals were set four weeks after release. Trapping occurred over a 4-night period, with traps set at dusk and checked at dawn. Upon capture, hare-wallabies were reweighed and body measurements taken to assess body condition.
Site fidelity: Radio-tracking showed that of those hare-wallabies that dispersed beyond 1 km from the initial release point, most (60%) did so within the first week. 42% of males dispersed beyond 1 km, but no females did. There was no discernable difference in site fidelity between hard and soft released individuals.
Body condition: Retaining hare-wallabies within a fenced enclosure prior to release had little impact on their body condition. At 63 days after release, overall, the body condition of the hare-wallabies declined marginally, and there was little difference in the condition of hard and soft released individuals (see Table 1, attached). Site fidelity had no effect on body condition.
Conclusions: The soft release protocol does not confer an advantage over the hard release protocol in terms of increasing site-fidelity or post-release body condition. Given that the financial cost of constructing pre-release enclosures will add significantly to the already high costs of undertaking a reintroduction programme a soft release protocol when reintroducing banded hare-wallabies is not considered worthwhile. Since similar results have been observed in other wallaby species (see, for example, Case 383), the merits of soft release protocols for re-introducing wallabies is debatable.
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