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Conservation in action: Rat eradication on Big Green Island
 

Jasmine Lee, May 2016

Big Green Island is a part of the Furneaux Group of islands, which are located off the North-east coast of Tasmania in the Bass Strait and are dominated by frequent and fierce winds. There are over 50 islands in the group, ranging in size from a couple of km2 to over 2000km2 for the largest of the group – Flinders Island, well known for its friendly locals and rugged beauty. Big Green is 3km off the west coast of Flinders Island and is only about 125 hectares (~1.25km2).

The southern tip of Big Green looking out at Chappell Island

The southern tip of Big Green looking out at Chappell Island

Though the Furneaux group was originally inhabited by Tasmanian Aborigines, by the time Tobias Furneaux (accompanying Captain Cook on his second voyage of discovery; 1773) arrived, it was thought to have been uninhabited for 6000 years. Soon after, word escaped about the hordes of seals in the Bass Strait Islands, and the sealers arrived in the late 1700’s. In 1831 it was decided to use Flinders Island as an Aboriginal settlement for remnants of displaced tribes from the Tasmanian mainland. The Aboriginal people used Big Green as a goose, mutton bird and sheep farm, where they would pinion (cut the birds pinion to prevent flying) the goose to keep them on the island. In the late 1840’s many of the islands were leased (being Crown land) to farmers for running sheep. Big Green was not initially leased but was regularly visited for muttonbirding and rabbit harvesting. Black rats (Ratus rattus) became established on the island sometime in the 1800’s. Mutton birds, or short-tailed shearwaters as they are formally known, have been an important food source in Tasmania since colonial times. In 1861 a Mr John Thomas described the island as “more or less a rookery of mutton birds… It is also most valuable as a rabbit warren. I have it on good authority that since last April, upwards of 1,200 rabbits have been taken off by different parties, and they are still so numerous that any person can go ashore and kill with sticks or stones 40-50 in a couple of hours”.

In 1865 a widowed Mrs Elizabeth Matilda Davis purchased the island and she began running sheep with her daughter Jane (formally Marie Antoinette Brown, it is not know why she was always called Jane). Elizabeth and Jane built themselves a life on the island, including building a modest dwelling and building stone walls by hand (which can still be seen today). The part of the building that still remains is heritage listed and belongs to the Tasmania Parks and Wildlife Service (PWS). Sheep farming has continued on the island since the times of Mrs Davis (sometimes an excess of 1000 animals were run), which combined with the rabbits – drastically changed the native vegetation.

Fred the sheep

Fred the sheep

The little heritage homestead

The little heritage homestead

Today the native Poa tussocks have been confined to belts around the west coast and the thistles, nettles and saltbush have been predominantly replaced by exotic grasses (maintained by the sheep grazing). In 1980 the island was sold to PWS and was declared a Nature Reserve, with the goal of establishing a safe place for Cape Barren Geese (the second rarest goose species in the world) to breed, as conflict with farmers prevented this on Flinders Island. Despite being a Nature Reserve, sheep grazing was continued to maintain the short grass, which the geese require. The current grazing lease belongs to Dennis Cooper, who maintains around 400 sheep on the island. Today, the island is a significant breeding site for the geese, and around 22,000 pairs of short-tailed shearwaters and 400 pairs of little penguins breed on the island. Though the rabbits have long since died out (due to harvesting and drought; 1914), until six weeks ago up to 20,000 black rats continued to compromise the ecological and agricultural values of the island, where they opportunistically predate upon seabird chicks/eggs and consume a large proportion of seed. The current leasee (Dennis) has made sporadic attempts to control the rats since 1984 using bait stations and rodenticides.

Cape Barren Goose

Cape Barren Goose

On the 7th of March 2016 PWS began an ambitious eradication program to permanently remove rats from the island. The plan was devised by PWS staff (notably Sue Robinson, who has vast experience in controlling invasive species) and eradication experts from New Zealand (the world leader in island eradications). The project has been largely supported by the Pennicott Foundation (Pennicott Wilderness Journeys are world famous for their ecotourism journeys from Bruny Island and the Tasman Peninsula). Under the excellent leadership of Sue, over 2,100 bait stations were installed by volunteers in a 25m x 25m grid over the entire island, including the two islets on the north of the island and also on the offshore rocky outcrops, commonly referred to as ‘The Reef’. Baits are deployed in stations to minimise impact on non-target species (such as pacific gulls). After allowing enough time for the rats to habituate to the stations, a second group of volunteers arrived to bait the stations with blue wax ‘Talon’ baits (the active ingredient is broadifaccoum, which is an anticoagulant). Though it can take them 3-4 days to die afterwards, Talon will kill rats with a single meal. Rebaiting of stations continued for 3 weeks until I arrived at the small airstrip in Bridport (north-east Tasmania).

Dereck having a nap

Dereck having a nap

Friday 13th May 2016

Along with nine other volunteers, I flew from Bridport to Flinders Island on a chartered light-aircraft with pilot Frank. We arrived on Flinders and explored the tiny town of Whitemark (named because of a white mark), where I was fortunate enough to meet the local celebrity – Derek the wombat. Soon enough we faced the windy weather and rough seas and were off on an ‘exciting’ boat ride to Big Green. We were met by an extensive welcoming party including the General Manager of PWS Peter Mooney, Rob Pennicott and his staff from Penicott Wilderness Journeys, and the ragged, albeit smiley volunteers, undoubtedly ready to get off the island and find a warm and dry bed.

Of course it began raining as soon as I started to pitch my tent, sheltered behind large non-native African boxthorn (the only trees on the island), and though they provide good shelter from the elements, they are not particularly friendly. Despite the weather we enjoyed a cheerful and memorable night with a potentially record-breaking party of 21 people on the island for the night. The highlight was watching the BBQ catch on fire (cheers to David for the excitement).

Tent safely tucked behind a boxthorn

Tent safely tucked behind a boxthorn

The following morning we were down to business and were soon off for training with Sue and Ranger Mark. After the departure of the VIPs that afternoon we quickly settled into routine and got to know one-another. Asides from myself, there was fellow PhD candidate Laura (also from the Antarctic Division), Diane who is an artist and a member of Tasmania’s Wildcare, Tony – a world-traveller and an engineer from Melbourne, Chris and Irene (Chris worked for Parks for 30yrs, following his participation in the Franklin campaign to prevent the damming of the Franklin and Gordon Rivers in south-west Tas), Cathie and David (Cathie also contributed to the Franklin Campaign and numerous other conservation projects in Tasmania), Leonie and Adrian (Adrian is a water race enthusiast and Leonie finds that water races conveniently turn up whenever Adrian plans an adventure), Sarah and Ranger Mark (currently enjoying the fishing on Flinders Island), Kerrie and Ranger Luke (Luke has worked on the eradication programs on Tasman Island and Macquarie Island), and of course – Sue (chief of this operation).

Boxthorns on the east coast

Boxthorns on the east coast

Dont want the stations to blow away...

Dont want the stations to blow away…

Over the next couple of days we deployed more talon and monitored for ‘nibbles’. Everything is recorded via an excellent app (Fulcrum), which we used on the ‘field’ iPads. The island is divided into 19 sections from north to south, each of which I became quite acquainted with over the ten days. In the first couple of days we found that uptake was extremely low (excluding one or two ‘hotspots’), indicating significant progress had already been made since the initial deployment of the baits three weeks prior, where the uptake was through the roof (4 baits were deployed in each station and had to be regularly replaced). In contrast, we cut down the number of baits in each station from 4 to 2 in coastal regions and 1 inland. However, we were eagerly awaiting the arrival of the new chocolate-flavoured bait (which we aptly nicknamed ‘death by chocolate’), so that we could deploy it and hopefully catch any of the rats that were ‘blue-phobic’ (aka not attracted to the Talon).

Laura baiting a station with Talon

Laura baiting a station with Talon

In the meantime the island maintained its reputation as being rainy and windy, and we ‘unfortunately’ were at times constrained to the tiny two-room heritage building to play cards and plan elaborate meals. I must say, due to the exceptional number of experienced cooks, we ate extremely well on the island (too well you might even say, if you counted the amount of chocolate we consumed). We were also entertained by the old newspapers on the walls, where Mrs Davis and her daughter had plastered the walls to keep the draughts out. There were such gems as ‘How to get a husband’, which consists of watching men eat soft-boiled eggs (I won’t ruin the ending – you have to look at the photo).

How to get a husband 101

How to get a husband 101

Severe weather warnings meant that the shearing shed became a dry utopia for some of our crew, where they would rather face the sheep smell than the wind and rain. Fortunately, my little tent proved to cope with the gale-force winds and hectic rains extremely well (thanks for the birthday present mum), and I was able to ‘enjoy’ being woken up by the little penguins at midnight and 4am multiple times (no really, I actually did quite enjoy it). Just so you can better picture the conditions, at one point Laura even checked the weather and informed me that it was windier on Big Green than it was on Macquarie Island… Of course Irene informed us that the previous group of volunteers had worse weather than us. Our nights normally consisted of a good feast, arguing over who got to do the dishes (seriously you had to be fast if you wanted to do dishes), gulping down some chocolate (or custard and apples) and waiting for Ranger Luke to entertain us. He did an exceptional job, where I am now well informed about the Tasman Island cat eradication, and enriched by hearing about some extraordinary wildlife encounters and interesting hobbies. These included rescuing stranded sperm-whales (Chris) and collecting old bicycles (and dusting them when required: Luke). Not to mention water races, whale sharks and cave spiders.

iPad app showing bait stations on The Reef

iPad app showing bait stations on The Reef

Off to bait The Reef with Ranger Luke

Off to bait The Reef with Ranger Luke

On Wednesday morning our dreams came true when the Flinders Island Police boat brought us the new bait, which we immediately began deploying on the north end of the island (in addition to the Talon). Despite some downpours, our enthusiasm meant the new bait had been deployed to every station by Friday afternoon, including to The Reef… In order to access The Reef we had waited to low tide (~4pm Thurs afternoon), before Luke and I attempted wading across the channel. I say attempted to wade, because by the end the water was over my chest. However, we made it safely and scrambled over the rocky crag and seabird haven to the ‘Last Outpost’, to deploy death by chocolate in the stations. We decided we had best sync the iPads before attempting the return crossing just in case we didn’t make it (joking). Thanks for the adventure Luke. This did mean a hot-shower upon return to the homestead, where Ranger Mark has ingeniously devised a hot-water camp shower in the shearing shed (thanks Diane for turning on the gas for me as my fingers were too cold to click the lighter!). As a side note, the afore mentioned hotspot in Sector 2 was still going strong, though we did find that the rats continued to eat the Talon (codename: ‘blue heaven’) and didn’t touch death by chocolate…

Nibbled baits next to new Talon, note the skull and crossbones

Nibbled baits next to new Talon, note the skull and crossbones

Our eagerness in getting all the new baits out meant that by the time Saturday rolled round we had little to do except for some casual monitoring. The day was spectacularly beautiful – not a cloud in site and for once no wind. We therefore hosted a cleaning party (ready for our departure the next day), ate as many pikelets as possible, snuck in some sneaky reading and games of crib, and explored the island at our leisure. For me this meant navigating the perimeter of the island stopping whenever I felt inclined to take a photo or watch birds, and checking bait stations whenever I practically walked on top of them. Pleasantly there was not a single rat nibble that I found, though sometimes the Talon was crawling with invertebrates. Turns out invertebrates like wax baits (they are able to metabolise the toxins). Our hotspot was also quiet – no new uptake. By the way the current record for bait consumed from a single station is 22.7 baits (thanks for the data updates John and Phil).

Beautiful weather

Beautiful weather

Though covered in sheep, the island is still extremely beautiful and I thoroughly enjoyed my time romping about the tussocks and among the mutton bird burrows (unfortunately, or perhaps fortunately for them the mutton birds had already left on their migration north). For the bird enthusiasts, I recorded twenty-two bird species on the island over the ten days, including some which were new for me (Cape Barren Geese, white-fronted chat, double-banded plover). The remoteness is peaceful and there were glorious sunrise/sunsets every day, not to mention a spectacular moon-rise over Mt Strzelecki (across the channel on Flinders Island) for our final night together.

Moon-rise over Mt Strezlecki

Moon-rise over Mt Strezlecki

Sunday morning meant our time together was coming to an end and it was time to depart. Of course our tents were wetter than they had been any morning on the island (the most dew I’ve ever seen). We all stood together watching the boats approaching to take us back to Flinders and I knew it was unfortunately time to go back to the real world (aka PhD life).

Hard at work

Hard at work

In early June another group of dedicated volunteers will arrive on the island to begin the monitoring phase of the project. Though we hadn’t seen hide-nor-hair of any rats in the last few days of our trip, monitoring the island for activity is an extremely important aspect to ensure the long-term success of the project. They will do this via a variety of measures, including monitoring the stations and deploying peanut-butter cards, which are plastic cards dipped in peanut butter (rats love peanut butter and will chew through the plastic to get the peanut butter). I’m hoping they don’t get any nibbles at all, which will be a very good sign for the wildlife of Big Green Island. Hopefully the eradication of rats will help the vegetation to recover and increase the breeding success of seabirds. Two years post baiting Sue will take the rodent detector dogs and deploy camera traps to verify that rats have been successfully eradicated.

Now back at my desk at the Antarctic Division I am extremely grateful to have had the opportunity to participate in such a project, where I was able to gauge conservation success with my own eyes (something that is often hard to do with desktop conservation projects). I loved the island and immensely enjoyed spending time with such wonderful and inspiring people. I have no doubt the success of such projects is underpinned by the dedicated teams of volunteers and staff. Since the beginning of this project, volunteers deployed 2,215 stations, made 21,104 observations, deployed 24,018 baits (480kg) and had 10,544 baits eaten (211kg). And I have no doubt the next group of volunteers will do an equally stellar job.

Big Green at dusk

Big Green at dusk

The crew

The crew