The number Tasmanian offshore islands where introduced vertebrate pests (e.g. rabbits, cats, rats, mice and goats) have been recorded and the islands where management plans provide information on the management of animal pests.
Introduced animal pests are perhaps the most invasive threatening agent impacting the conservation of native plants and animals on Tasmania's offshore islands. On these islands, the impact of introduced pests is often devastating. For example, on some islands introduced pests have caused major declines and extinctions of native species, especially seabirds.
The removal of animal pests from Tasmania's offshore islands is vital to ensure the integrity of these island ecosystems. This is especially important when considering the potential impact of the European red fox (Vulpes vulpes) on native species since its introduction onto the Tasmanian mainland since 2001. The fox represents the single most devastating threat to Tasmania's native mammals and birds. If this species significantly impacts native species on Tasmania's mainland, our offshore islands will increasingly offer important safe havens for the protection and preservation of native species that may otherwise become threatened or extinct on mainland Tasmania due to predation by the fox, or by this environmental pest competing with native species for food and habitat. Offshore islands also offer protected safe havens for native species impacted by other environmental pests..
The maintenance of island ecosystems is also essential for the maintenance of genetic diversity. Offshore islands often support species that are genetically distinct from their mainland counterparts such as the golden wombat (Vombatus ursinus Ursinus), which is now restricted to Flinders Island.
The number of offshore islands where animal pests are known to be (or have been) present is a direct measure of their ecological condition. The number of offshore islands where management plans include measures to control or eradicate animal pests also provides a measure of management response and the potential to limit their environmental impacts.
There are a number of significant constraints on the capacity to monitor and report on introduced animal pests known to occur on Tasmanian offshore islands. Given that Tasmania has over 330 offshore islands, both large and small, not all have been surveyed due to their remote location and the resource constraints faced by those conducting monitoring and research.
Despite the substantial number of introduced animals known to occur on many of our offshore islands, very little is known about their pest status or their impacts upon native species or ecosystems. Our knowledge is limited to general survey work that has been conducted on a selected number of islands. It is also based upon opportunistic assessment when other activities have been undertaken on an island or anecdotal reports from the general public.
The assessment of introduced animals on offshore islands has often focused on island subset groupings. For example, these subsets might select a range of islands of a certain size range, large islands with characteristics similar to the Tasmanian mainland or islands that hold a conservation classification. The assessments have also focused upon vertebrate mammals and generally omit introduced bird species. No easily accessible data was available to assess the impacts of introduced invertebrates on islands. In addition, when data are collected on introduced animal pests, they are often held by a variety of organisations and in a variety of formats.
Therefore, any overall assessment of introduced animal pests on offshore islands requires combining various data sets and is invariably 'vertebrate mammal focused'. It was not possible to verify the original sources of the various baseline data records and therefore, it is not possible to identify when the introduced species were last sighted on the islands included in the indicator.
Reliable and comprehensive data is needed to assess the impact of introduced animal pests on our offshore islands. Comprehensive data helps to inform decision-makers and the general public so they are able to implement appropriate management action to reduce the environmental threat associated with the introduction of pest species to these unique and remote places.
This indicator draws largely from the 2005 report that was prepared by DPIWE (now DPIPWE) for the Commonwealth Government. At the time, DPIWE identified that 55 offshore islands, which were 20 hectares in size or larger, were found to have feral (pest) and/or introduced animals present (Internal linkDPIWE 2005). This indicator also draws on data presented in the 2003 SoE Report because not all offshore islands with known introduced animals are detailed in the 2005 DPIWE Report (Internal linkRPDC 2003).
Three pieces of legislation regulate the introduction and movement of animals within Tasmania, both native and introduced, and they are relevant to the managament and control of introduced animals on our offshore islands. They are: 1) the External link: LegislationNature Conservation Act 2002; 2) the External link: LegislationNational Parks and Reserves Management Act 2002; and 3) the External link: LegislationAnimal Health Act 1995.
Introduced animals on Tasmanian offshore islands
Tasmania has over 330 offshore islands, large and small, dotted around the Tasmanian coastline. Of these, 65 are 20 hectares in size or larger (Internal linkDPIWE 2005). The following four maps provide information on Tasmanian offshore islands 20 hectares or larger, their land tenure status and whether there are, or have been, any introduced vertebrate animals known to occur on them. The interactive maps provide various summary measures with the data linked to the any relevant information on each of the islands and introduced vertebrate animals known to occur on them (requires External linkAdobe SVG Viewer).
The largest Tasmanian offshore islands, including King Island, Flinders Island, Cape Barren Island and Clarke Island in Bass Strait, Schouten Island in the east and Bruny Island in the south-east are not included in the following assessment of introduced animals on Tasmanian offshore islands because they are considered to have similar characteristics as mainland Tasmania in terms of introduced and/or feral animals. In this respect, the last SoE Report in 2003 reported that King Island was impacted by cats, rats and mice; Flinders Island was impacted by cats and pigs; Cape Barren island was impacted by cats, rats and mice; Clarke island was impacted by rabbits, cats and rats; and Bruny Island was impacted by rabbits, cats, rats and mice (Internal linkRPDC 2003). Goats herds have been present on King, Flinders and Bruny islands in the past but have now been eradicated. The 'Freycinet National Park and Wye River State Reserve Management Plan 2000' states that rabbits are found on Schouten Island (Internal linkPWS 2000).
In addition, introduced birds (including the common starling, house sparrow, gold finch, green finch, European blackbird and Indian myna) are not included in this assessment because their impacts on offshore islands are potentially similar to those experienced on the Tasmanian mainland. Information on introduced animal pests in Tasmania is detailed in the Internal linkAnimal Pests and Diseases Indicator.
Native animals have also been introduced onto some of Tasmania's offshore islands (e.g. eastern grey kangaroos onto Three Hummock Island; Forester kangaroos, eastern barred and brown bandicoots, Bennett's wallabies, brush tail possums and emus onto Maria Island; Tasmanian devils onto Badger Island; Bennett's wallabies onto Deal Island; and tiger snakes onto many Tasmanian islands in the1960s and 1970s). These species are not included in this assessment because this indicator focuses on non-native introduced species.
The most common introduced animal identified in 2005 was rabbits. Rabbits were present on 23 of the offshore islands identified in the proceeding maps and included in the following table. Cats, mice and rats were also common, and were found on 17, 11 and 10 islands respectively. In many instances the species of feral rat was not established. In addition, cattle were found on 11 islands and sheep were found on 10 islands.
A: Offshore islands Source: Internal linkDPIWE 2005 B: Pest free islands Source: Internal linkDPIWE 2005 C: Introduced pests Source: Internal linkDPIWE 2005 D: Archipelagos Source: Internal linkDPIWE 2005
A: Offshore islandsinternal SOE link to larger image
Source: Internal linkDPIWE 2005
B: Pest free islandsinternal SOE link to larger image
Source: Internal linkDPIWE 2005
C: Introduced pestsinternal SOE link to larger image
Source: Internal linkDPIWE 2005
D: Archipelagosinternal SOE link to larger image
Source: Internal linkDPIWE 2005
When the data is combined, the most common introduced animal is rabbits. Rabbits are known to be present on 29 of Tasmania's offshore islands. Cats, rats, and mice are also common, and they are found on 22, 17 and 14 islands respectively.
In total, 69 Tasmanian offshore islands are identified as having, or having had, populations of introduced pest animals. This represents a 15% increase from the last SoE Report (59 islands were reported against in 2003) in the number of islands reported with a known population of introduced animals at some stage in the past.
Number of offshore islands with introduced vertebrate pests Caption: Not all Tasmania's offshore islands have been surveyed for introduced vertebrate pests. The table below shows the offshore islands that are known to have animal pests.
Number of offshore islands with introduced vertebrate pests
Caption: Not all Tasmania's offshore islands have been surveyed for introduced vertebrate pests. The table below shows the offshore islands that are known to have animal pests.
The embedded Internal linktable titled 'Introduced Vertebrate Pests on Tasmanian Offshore Islands' provides a more detailed list of introduced vertebrate pests that are known, or have been recorded, on the Tasmanian offshore islands detailed above.
The following table provides a list of management plans that include information on the management of animal pests and/or introduced animals on Tasmanian offshore islands.
Environmental pests on offshore islands covered by control/eradication plans, April 2008 Caption: Management plans that provide information on the management of feral animals on Tasmanian offshore islands in Tasmania
Environmental pests on offshore islands covered by control/eradication plans, April 2008
Caption: Management plans that provide information on the management of feral animals on Tasmanian offshore islands in Tasmania
In addition to the finalised management plans and operational planning objectives detailed in the above table, the Department of Tourism, Parks, Heritage and the Arts (DTPHA) completed drafts for three management plans in 2002 that that were reviewed by the Resource Planning and Development Commission (RPDC) in 2003. The draft management plans aim to provide more specific management direction and guide development for a number of specified island reserves for 10 years from 2002. The following draft management plans have not been finalised, nor have they been implemented, due to resource constraints:
A 'Feral Pig Management Plan for Flinders Island' was also developed in 2001 by DPIWE with funding from the Natural Heritage Trust Grant, although at the beginning of 2008 the plan was yet to be funded or implemented (Internal linkCopson 2001).
An indicator can show trends or changes that apply to one or more environmental issues. The data within an indicator is used to inform an issue report and any related recommendations. A summary of the indicator's relevance to a particular issue can be found within the 'Indicator' section of each of the linked issue reports below.
Rosemary Gales; Drew Lee; David Pemberton
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