Macropod Management, Maria Island National Park: Annual Report and Recommendations June 2019

The recommendation for Macropod Management in 2019 is for a maximum of 250 Bennetts wallabies (Macropus rufogriseus rufogriseus), 450 Tasmanian pademelons (Thylogale billardierii) and 50 large adult male Forester kangaroos (M. giganteus) be culled on Maria Island National Park. This recommendation is the outcome from careful consideration of the results from this year’s Integrated Monitoring Strategy (2010). For example, Pasture Monitoring indicates reduced vegetation cover at Darlington, Hopground and French’s Farm, and a decrease in pasture biomass for each site during autumn 2019. Population Monitoring results indicate an increasing population trend estimate for Forester kangaroos and Tasmanian pademelons, while Bennetts wallaby trend estimates remain constant despite being culled in three out of the past five years. Evidence from Biological Monitoring shows that intense grazing pressure has already affected animal health as indicated by anaemia and fatty liver change in all three species. In addition, rainfall for eight out of the past twelve months has been below average; rainfall forecasts indicate dry conditions for the next three months, from June to August; and, below average rainfall is likely in spring 2019. The only available water on the island is retained at Bernacchi’s Creek at Darlington and Four Mile Creek further south. There is no standing water in any of the ephemeral lagoons at Pt Lesueur or in the drainage channels at French’s Farm. Under an adaptive management framework for decision making, management intervention to cull Forester kangaroos, Bennetts wallabies and Tasmanian pademelons on Maria Island National Park is warranted this winter due to low pasture and water resources; high nutritional stress and intestinal parasite burdens; and limited impacts on marsupial herbivore recruitment (i.e. population growth) from predation.

The current estimated population of Tasmanian devils (Sarcophilus harrisii) on Maria Island (n = 60-70), as advised by the Save the Tasmanian Devil Program (STDP), are unlikely to have significant impacts on macropod recruitment in the coming breeding season. The introduction of devils to Maria Island has been primarily to safeguard a healthy population in isolation from the Devil Facial Tumour Disease (DFTD) but may also have a dual benefit in reducing the number of marsupial herbivores over time. However, devils primarily prey on small and vulnerable species such as ground nesting bird species and juvenile macropods and bare-nosed or common wombats (Vombatus ursinus), but not healthy adult Forster kangaroos, Bennetts wallabies or common wombats. Population monitoring results indicate increasing trend estimates for Forester kangaroos and Tasmanian pademelons; a high - but not increasing trend for Bennetts wallabies; and, a slightly decreasing trend estimate for common wombats. Forester kangaroo population trend estimates are the lowest of all marsupial herbivores on Maria Island, however as the largest marsupial in Tasmania, Forester kangaroos are a consistent primary grazer contributing to the current intense grazing pressure.

Intense grazing pressure is indicated by a high percentage of macropods with fatty liver change (a key indicator of nutritional stress) and anaemia (caused by nutritional stress and/or high intestinal parasite burdens). Both indicators were high in Forester kangaroos (79% and 100% respectively) and Bennetts wallabies (86% and 100% respectively). Tasmanian pademelons had moderate fatty liver change (53%) while most sampled pademelons had anaemia (93%). Forester kangaroos, Bennetts wallabies and Tasmanian pademelons have high to moderate intestinal worm (parasite) burdens, although Bennetts wallabies and Tasmanian pademelons have consistently higher worm eggs per gram (epg) counts than Forester kangaroos. High numbers of intestinal parasites are also an indication of intense grazing pressure on already contaminated pasture; the lack of dispersal opportunities on an island; and, reduced pasture growth from an extended period of low rainfall. Should rainfall exceed the forecast levels, cold winter temperatures would reduce the potential for good pasture growth during winter months. Fecundity (the percentage of females with pouch young) is high for Forester kangaroos, Bennetts wallabies and Tasmanian pademelons due to above average rainfall in November 2018 and February 2019, and due to all three species retaining an embryo at the blastocyst stage for delayed implantation. The kidney fat index (KFI), an indicator of body condition, was low for Bennetts wallabies (32%) and Forester kangaroos (26%) but higher for Tasmanian pademelons (98%). Forester kangaroos have not been culled on Maria Island since 2013, and Tasmanian pademelons were culled in low numbers in 2018 for the first time since 2013.

As endorsed by the Maria Island National Park and Ile Des Phoques Nature Reserve Management Plan, 1998 (Section 19.5, pp 64) and the Maria Island Macropod Management Program (MMMP) Directions Statement (2011), culling to reducing grazing pressure on Maria Island aims to improve animal welfare for the remaining population of marsupial herbivores on the island during the upcoming winter period. The current indications of nutritional stress and limited food and water resources would result in adverse animal welfare outcomes if a cull does not occur. This decision has been made in consultation with an experienced veterinarian and following discussions between all agencies involved in the MMMP, including input from the Save the Tasmanian Devil Program (STDP). The number of Tasmanian devils on Maria Island has been reduced since 2016 to below the estimated carrying capacity (i.e. 80 – 120 devils) following the removal of suitable adults and pouch young for the Wild Devil Recovery Project (STDP 2019). The lower density of devils is expected to have limited impacts on macropod population growth due to alternative prey species being available on Maria Island. Climate forecasts from the Bureau of Meteorology (2019) indicate only a low (27%) chance of exceeding median rainfall this winter, with the long-term weather outlook indicating a higher chance of El Niño forming in 2019 resulting in below average winter and spring rainfall further limiting the potential for pasture growth in spring and early summer on Maria Island.