Long-nosed potoroo (Potorous tridactylus) population, Cobaki Lakes and Tweed Heads West - endangered population listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Cobaki Lakes and Tweed Heads West population of the Long-nosed Potoroo Potorous tridactylus (Kerr 1792) in the Tweed local government area as an ENDANGERED POPULATION in Part 2 of Schedule 1 of the Act. Listing of endangered populations is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Long-nosed Potoroo,  Potorous tridactylus (Kerr 1792), is not currently listed as an endangered species in Part 1 of Schedule 1 and as a consequence populations of this species are eligible to be listed as endangered populations. The species is currently listed as vulnerable in both NSW and under the federal  Environment Protection and Biodiversity Conservation Act.

2. A population of Long-nosed Potoroos is known from the Tweed Local Government Area, north-eastern NSW, in a small area of Crown land between the northern shore of Cobaki Broadwater and the NSW-Queensland border (Mason 1993, Bali et al. 2003). The area occupied by this population is defined by the localities of Cobaki Lakes and Tweed Heads West (Geographical Names Board of NSW 2004).

3. The Long-nosed Potoroo is a medium-size potoroid about 38cm tall and weighs up to 1.6kg (Johnston 2000). Individuals are brown to grey above and paler below, and the snout is long and tapering.

4. The Long-nosed Potoroo is distributed from south-eastern Queensland through NSW and southern Victoria to South Australia. The species also occurs in Tasmania and on Bass Strait islands. In NSW, the species has a patchy distribution along the east coast and hinterland (Johnston 2000).

5. Long-nosed Potoroos are generally restricted to areas with an annual rainfall greater than 760 mm where they inhabit dry and wet sclerophyll forests and woodland with a heathy understorey with the preferred habitat in north eastern NSW being dry and wet open shubland (Mason 1997, Johnston 2000, Milledge, pers. comm.). The species requires relatively thick ground cover growing on friable soils. They dig small holes in search of roots, tubers, fungi and soft-bodied soil-dwelling animals. Long-nosed Potoroos breed throughout the year with peaks at the end of winter or early spring, and again in late summer. Females tend to begin breeding at one year of age and a single pouch young is reared at a time. Individuals can live for up to seven years in the wild (Johnston 2000).

6. The Cobaki Lakes and Tweed Heads West population occupies an area of forest-heathland of between 100 and 150ha and the total population is estimated to number less than 100 individuals (Bali et al. 2003). This Long-nosed Potoroo population is completely disjunct from other populations in the south and west. The nearest Long-nosed Potoroo records are at Knights Forest adjacent to Cudgen NR, 20km to the south dating from 1988, 1989 and 2004 (Milledge 1988, P. Catling, pers. comm., Conservation Ecologists Association,  in litt.). These records may represent another population under threat.

7. The habitat occupied by the Cobaki Lakes and Tweed Heads West population is bordered by residential and industrial development, as well as land zoned for future development. An access track with a 49m easement width was constructed through the habitat in 1993. Radio tracking and recapture studies of Long-nosed Potoroos from the Cobaki population found that individuals did not cross this access track (Bali et al. 2003), suggesting that the access track presents a barrier to Long-nosed Potoroo movements and now divides the population.

8. The Cobaki Lakes and Tweed Heads West Long-nosed Potoroo population is threatened by the loss and degradation of habitat. The surrounding lands in the Tweed Local Government Area have been cleared for agriculture and remnant stands of habitat along the coast and hinterland are threatened by expanding urban development. Edge effects and alterations to natural fire regimes reduces the availability of suitable habitat for the Long-nosed Potoroo (Mason 1997), and the population's small size and isolation from conspecifics makes it vulnerable to extinction by stochastic events (Banks 2004).

9. The Cobaki Lakes and Tweed Heads West Long-nosed Potoroo population is threatened also by predation from exotic predators such as the European Red Fox, Vulpes vulpes, and both feral and domestic cats,  Felis catus. The species may also be forced to compete with Feral Pigs,  Sus scrofa, for food items such as fungi and soil-dwelling invertebrates. Small populations of critical weight range mammals living close to urban centres are particularly sensitive to extinction by predation (Banks 2004).

10. In view of the above points the Scientific Committee is of the opinion that the Cobaki Lakes and Tweed Heads West population of Long-nosed Potoroo Potorous tridactylus (Kerr 1792) in the Tweed Local Government Area is facing a high risk of becoming extinct in nature in New South Wales, it is disjunct and near the limit of its geographic range, and it is not a population of a species already listed on Schedule 1. Consequently, the Scientific Committee considers that the population is eligible for listing as an endangered population on Part 2 of Schedule 1 of the Act.

Associate Professor Paul Adam
Chairperson
Scientific Committee

Proposed Gazettal date: 03/12/04
Exhibition period: 03/12/04 - 28/01/05

References

Bali R, Lewis B, Brown K (2003) 'The status and distribution of the Cobaki Long-nosed Potoroo population.' Unpublished report prepared for Parsons Brinckerhoff, Brisbane.

Banks PB (2004) Population viability analysis in urban wildlife management: modelling management for Sydney's quarantined bandicoots. In 'Urban Wildlife'. (Eds D Lunney and S Burgin) pp. 70-77. (Royal Zoological Society of NSW: Mosman)

Geographical Names Board of NSW (2004) Cobaki Lakes Locality and Tweed Heads West Locality were assigned 23 May 2003 and are shown on map GNB3810. Retrieved 8 July, 2004, from Geographical Names Board of NSW website.

Johnston PG (2000) Long-nosed Potoroo Potorous tridactylus (Kerr, 1792). In 'The Mammals of Australia.' (Ed. R Strahan) pp. 575-576. (Reed Books Australia: Chatswood)

Mason R (1993) 'Report on the Long-nosed Potoroo (Potorous tridactylus) at Cokabi.' Unpublished report to the NPWS, Northern Region, Grafton.

Mason R (1997) Habitat use and population size of the Long-nosed Potoroo, Potorous tridactylus (Marsupialia: Potoroidea ) in a coastal reserve, north-eastern New South Wales.  Australian Mammalogy 20, 35-42.

Milledge D (1988) A survey of the vertebrate fauna of the Round Mountain - Cudgen Lake Area. Unpublished Report to the NPWS, Northern Region, Grafton.