Maria Island Devil Translocation Project Update July 2015
The establishment phase of the Maria Island Devil Translocation Project has been successfully completed with 28 devils released over two years and evidence that the introduced population has bred successfully over the 2013 and 2014 breeding seasons. The focus is now on monitoring the devils, along with the potential impacts of the expanding population on other native species and the island's ecology.
Establishing this first protected population of healthy Tasmanian devils in the wild was an important conservation step for the Save the Tasmanian Devil Program. The potential impacts of the devil introduction on the natural and cultural values of Maria Island National Park were assessed in favour of the long term benefits to the endangered Tasmanian devil. The Maria Island population is helping to maintain wild devil behaviours in the Insurance Population - established to guard against the species' extinction - and it will provide a source of suitable devils for reintroduction on mainland Tasmania as soon as required.
Devil population monitoring
The Maria Island devil population is estimated at between 70 and 90 animals, made up of around 60 offspring produced over the past two breeding seasons. Of the original 15 devils released in 2012, one adult male devil has been confirmed dead and another is believed to be deceased. The remaining 26 devils released in 2012 and 2013 have all been accounted for, either through trapping or remote camera images, between July and November this year. In general, all the devils appear to be in good condition, having adapted well to the environment on Maria Island and life in the wild.
From the most recent devil monitoring trip in April 2015 (see the Summary Trip Report ) combined with observations over the past 18 months, there is evidence that around 20 offspring were produced in 2013 and as many as 40 this year. Of these, 15 first generation and 8 second generation island-born young have so far been identified, named and micro-chipped.
The breeding estimate is based on trapping surveys, giving the number of pouch young or active teats of female devils (post denning) and the number of previously unidentified offspring; as well as images on remote cameras of females carrying pouch young and images of unidentified juveniles. A more accurate estimate of the total population, which depends on the successful weaning of young from the 2014 breeding season, will be possible next year as more offspring are identified.
Devil population management and genetic research
As the population grows, the Island will near its carrying capacity for Tasmanian devils, which has been estimated at around 120 individuals. As it does so, the Program must manage the genetic diversity of the colony as well as total devil numbers. A key strategy for achieving this is to monitor breeding and select particular devils, whose genes are well represented in the population, for removal from the gene pool. The selected devils may be transferred from Maria Island back into the wild on mainland Tasmania or kept on the island but restricted from breeding through contraception.
The Program is investigating contraception as a tool to assist in managing the genetics of small populations and trials are planned on Maria Island in the coming year. This is part of a collaborative study with the University of Sydney (USyd), the Zoo and Aquarium Association (ZAA) and Taronga Zoo Conservation Society. Several female devils on Maria Island that are known to have bred in the past two seasons, will receive a contraceptive implant prior to the 2015 breeding season. The aim is to prevent a potential oversupply of their genes and to maintain the genetic diversity of the population. If the trial is successful, contraceptive implants may be an additional tool for limiting the Island's devil population growth.
This research, and the genetic management of the Maria Island population, is being supported by another important study into the genetic makeup of the devil population. The Program, ZAA and USyd have been funded by the San Diego Zoo Global to conduct research into the development of an innovative genetic assay technique that will assist in determining the parentage of each offspring of the Maria Island population. This will provide the basis for decision making regarding the selection of devils for contraception or removal from the population in future, as well as the need to supplement it with new genetic stock.
Monitoring and assessment of impacts
The Program has been monitoring the impact of the growing devil population on the island's ecology and on terrestrial fauna and ground nesting bird species, in particular. The potential risks to these species and the ecological values in general, were considered during the assessment phase of the translocation project. As part of the approval process, the Program collected baseline data on a range of species and developed a long term monitoring strategy, which includes a set of environmental indicators to assess potential impacts.
This scientific framework for the long term monitoring and assessment of impacts is a key focus of the joint management agreement with the Parks and Wildlife Service (PWS). If and when these environmental indicators or ‘triggers' are reached, a decision will be made on whether further monitoring is needed, or whether action is required to reduce the risks to other species and/or manage the devil population. The aim is to safeguard the important environmental and cultural values of the National Park in balance with the long term benefits for the recovery of the endangered Tasmanian devil.
Surveys of other native species
According to devil scat analysis over the two years since the introduction began, the devils on Maria Island have a varied diet, with a number of species being preyed upon or scavenged. Their staple includes possums, birds, wombats and pademelons but smaller traces of echidna, Bennetts wallaby, bettong, Forester kangaroo, ringtail possum and bandicoots have also been identified in scats. However, the actual variety of prey is likely to be greater because the analysis technique is limited for detecting soft-bodied species.
Localised populations of ground nesting birds on Maria Island are at risk from a number of impacts and are particularly vulnerable to predation by devils. Surveys of little penguins, native hens, shearwaters and Cape Barren geese populations, for instance, are being undertaken at scheduled times each year to enable an objective assessment of the potential impact of devils.
Recent surveys of the little penguin population on the island indicates that while breeding colonies in the more remote locations appear to be coping with the presence of devils, the small colony at Darlington has been impacted significantly. Whilst some direct predation by devils is evident, the impact may also be indirect with wombats competing against the penguins for burrow space, possibly to protect themselves against devils. The initial response by the PWS and devil management group is to try to reduce the impact by increasing the safety and available nesting sites for penguins at the Darlington colony. Hence, several artificial nesting burrows will be built on at the colony site and situated closer to the water's edge to safeguard the nesting birds and chicks this summer.
Nesting behaviour of Cape Barren geese around Darlington appears to have been affected with no successful breeding this season, although some pairs have continued to breed on the island off Maria's north coast. This impact was predicted, and although it appears significant, it must be assessed in the context of the total number of Cape Barren geese across their natural range in Tasmania. Given that this number has increased markedly since the geese were first introduced to the island in the 1960s, after the species suffered a state-wide population decline, the significance of the impact to this localised population on mainland Maria Island is somewhat reduced.
Surveys of the short-tailed shearwater and native hen populations, meanwhile, are ongoing this season and potential impacts will be assessed in coming months. There is evidence of predation by devils on shearwaters at one of the colonies on the island, causing a reduction in predation of the birds by feral cats and brush-tailed possum. Meanwhile, a broad scale survey of fauna is undertaken four times per year using remote cameras, covering the complete range of habitat types on the island. This monitoring, which began prior to the introduction of the devils, is providing data for comparative analysis against the baseline and will assist in identifying any widespread impacts of devils on the Island's ecology.
Future management focus
The Program will continue to monitor the devil population and its impact on other species, and work closely with PWS under the joint management agreement in response to measured indicators. Monitoring of these indicators (or triggers) will help to ascertain the Island's carrying capacity for devils - before it reaches a maximum point. Given the breeding success of the introduced population, not to mention the complexity of environmental interactions, the focus of the Program will be on the precautionary removal of devils and their reintroduction into areas of mainland Tasmania in coming years.