Predation by the ship rat on Lord Howe Island - key threatening process listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Predation by the Ship Rat Rattus rattus on Lord Howe Island as a KEY THREATENING PROCESS on Schedule 3 of the Act. Listing of Key Threatening Processes is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. Rattus rattus (Linneaus, 1758), Ship Rat (also known as Black Rat, Roof Rat or Alexandrine Rat) was introduced accidentally to Lord Howe Island in 1918 from a ship grounding. The population of Rattus rattus increased dramatically soon after establishment, and is now distributed widely in terrestrial habitats on the Island.

2. Rattus rattus has a generalist diet, and is known to take seeds, green plant material fungi, invertebrates, small vertebrates and eggs as food. Overseas research has documented negative impacts of this rat on invertebrates, lizards and birds (Atkinson, I.A.E. 1973. J. Roy. Soc. N.Z. 3, 457 - 472; Atkinson, I.A.E. 1977. Pacific Science 31, 109 - 133; Atkinson, I.A.E. 1985. In Conservation of Island Birds, ed. P.J. Moors, 35 - 81; Dingwall, P.R. and others, eds. 1978. Department of Lands and Survey Information Series 4, New Zealand).

3. On Lord Howe Island, Rattus rattus has been implicated in the decline and extinction of five species of birds, the Vinous-tinted Thrush Turdus xanthopus vinitinetus, Robust silver-eye Zosterops strenua, Lord Howe Island Warbler Gerygone insularis, Lord Howe Starling Aplonis fuscus hullianus and Lord Howe Fantail Rhipidura cervina.

4. Two species of lizards, the Lord Howe Island Gecko Christinus guentheri and Lord Howe Island Skink Pseudemoia lichenigera are scarce on the main island of Lord Howe, where Rattus rattus occurs, but occur more abundantly on small islands where the rat is absent.

5. Rattus rattus has been implicated in the extinction of two large-sized land snails that lived in the southern mountains of Lord Howe Island, a subspecies of Placostylus bivaricosus and an endemic genus and species Epiglypta howinsulae. The extant and endangered land snail Placostylus bivaricosus bivaricosus is at risk from rat predation, as is the large land snail Gudeoconcha sophiae. Rattus rattus has been further implicated in the extinction of the Lord Howe Island Phasmid Drycocelus australis from the main island, although this endangered species may still occur on Balls Pyramid where rats are absent. Both Drycocelus australis and Placostylus bivaricosus are listed as endangered species on Part 1 of Schedule 1 of the Threatened Species Conservation Act.

6. Rattus rattus is known to damage the vegetative parts of several species of plants on Lord Howe Island and to deplete seed yields of the palms Howea forsteriana and Lepidorrhachis mooreana and other species.

7. A Threat Abatement Plan addressing Predation from Rattus rattus should recognise and augment the existing rat control program on Lord Howe Island. It should also address potentially undesirable consequences of rat control, in particular the potential for increase in House Mouse Mus domesticus populations in control areas.

8. In view of 2 - 6 above, the Scientific Committee is of the opinion that Predation by the Ship Rat, Rattus rattus on Lord Howe Island adversely affects two threatened species and could cause species or populations that are not threatened to become threatened, and therefore is eligible to be listed as a Key Threatening Process under the Act.

Gazetted: 12/5/00
Exhibition period: 12/5/00 - 9/6/00