Jon Marsden-Smedley
Figure 1. The project supports multiple bird species including the vulnerable (a) Hooded Plover, (b) Australian Pied Oystercatcher, (c) Sooty Oystercatcher and (c) the critically endangered Orange-bellied Parrot. (Photos J. Marsden-Smedley)
Introduction. The Tasmanian Wilderness World Heritage Area (TWWHA) in the southwest of Tasmania is an important area for conservation. The coastline of this region has high natural integrity and is a major stronghold for a number of shore-nesting and feeding birds including the vulnerable Hooded Plover (Thinornis cucullatus), Australian Pied Oystercatcher (Haematopus longirostris), Sooty Oystercatcher (Haematopus fuliginosus) and the critically endangered Orange-bellied Parrot (Neophema chrysogaster) during its migration (Fig. 1). Three ecosystem-transforming weed species: Sea Spurge (Euphorbia paralias), Marram Grass (Ammophila arenaria) and Blackberry (Rubus fruticosus aggregate) have the potential to transform the coastline’s geomorphic structure and have been identified as major threats to environmental and cultural value. It is estimated that about 425 km of the 850 km coastline in the TWWHA is susceptible to Sea Spurge and / or Marram Grass invasion.
The WildCare volunteer group SPRATS (Sea sPurge Remote Area TeamS) has been undertaking annual weed management works along the TWWHA coastline between Cape Sorell (Macquarie Harbour) and Cockle Creek since 2006 (Fig. 1). SPRATS is a self-managing volunteer group working in partnership with the Tasmanian Parks and Wildlife Service (PWS). The primary goal of the program is to initially control and then eradicate Sea Spurge and Marram Grass from the coastline (Figs 2-4). The secondary goal is to eradicate any Blackberry infestations found and monitor for other weeds.
Figure 2. The SPRATS work area.
Logistics. The SPRATS weeding program has divided the coastline into eight sectors. At the start of each weeding season, detailed maps are prepared showing weeding sites, campsites and walking routes. These data are uploaded into GPS units so that all groups can efficiently and easily locate previously recorded weed sites, campsites and walking routes. Teams of SPRATS volunteers walk each section of the coastline of the TWWHA annually. While undertaking weed control and monitoring, volunteers also record information on rare and threatened shorebird species, assist with research into the ecology of the region (e.g., collection of Tasmanian Devil scats for genetic analysis), record the location of Aboriginal cultural sites (e.g., petroglyphs, stone arrangements, middens and hut sites) and the usage of the area by other groups (e.g., quad bike riders).
Works undertaken. In the first three years of the program, weeding efforts were concentrated in the southernmost susceptible areas. Once these Sea Spurge infestations had been given an initial knock-down, efforts moved to very large infestations along 45 km of coast south of Cape Sorell. Work then expanded to include about 160 km of coastline in Macquarie Harbour.
Trials were conducted in 2009-2010 to compare both the kill rates of target species and impacts on non-target species of different herbicide treatments. These trials identified glyphosate mixed with Pulse® as the best herbicide treatment for Sea Spurge.
Different strategies have been utilised at different stages of the program. Heli-spraying operations have been used to knock down very large Sea Spurge infestations (i.e., infestations of > 250,000 plants) and the subsequent massive seed germination event. Two rounds of heli-spraying reduced the number of Sea Spurge plants by 90% and enabled subsequent hand weeding. The optimum technique identified for treating Marram Grass was to spot spray with Haloxyfop-R methyl ester and penetrant. This is followed up by hand weeding once weed densities are reduced.
A feature of the SPRATS work program is collection of geo-referenced data on all weeds removed, along with targeted research into the most effective treatment methods. These data are used to demonstrate work effectiveness, plan annual work programs and report back to the PWS and other funding bodies.
A major development in the past two seasons has been testing and spreading the Sea Spurge biocontrol recently developed by the CSIRO. This biocontrol has the potential to provide a long term solution to the issues associated with Sea Spurge. From 2006 to 2022-23, 8504 work days have been completed, most of which has been volunteer effort.
Figure 3. A SPRATS volunteer standing in a patch of Sea Spurge at the Sassy Creek site in 2007. (Photo J. Marsden-Smedley)
Figure 4. The Sassy Creek site in 2021. (Photo J. Marsden-Smedley)
Results to date. Prior to the start of the program it was estimated that the TWWHA region contained about 11.1 million Sea Spurge plants and about 124 000 Marram Grass clumps located in over 700 sites. By 2022-2023 weeds had been mapped from over 850 sites, made up of about 700 Sea Spurge, 150 Marram Grass, four Blackberry, three Great Mullein and one Slender Thistle. To date the SPRATS program has removed over 14.4 million Sea Spurge plants (about 99.7%). In the 2022-2023 weeding season about 2795 clumps of Marram Grass were sprayed representing a 98% reduction on the pre-SPRATS number of marram grass clumps. The region’s known blackberry infestations have been eradicated.
Challenges. A major challenge is missed Sea Spurge sites. In its second year of growth, Sea Spurge produces a large number of seeds which then germinate or replenish seed banks. Seedlings from these reactivated sites are responsible for between a third and half of Sea Spurge plants treated and the rate at which SPRATS is reducing the number of Sea Spurge is slowing. It appears likely that there are an increasing number of Sea Spurge seeds washing in from very large infestations to the north of the TWWHA and also along the east coast of Tasmania. If the Sea Spurge biocontrol is found to be effective, this issue should be addressed by large scale spreading of the biocontrol agent which should reduce these very large infestations. It may also be necessary to do targeted releases of the biocontrol within the TWWHA.
In the early years of SPRATS operations, treating Marram Grass was rated as a lower priority than Sea Spurge. Marram Grass identification and weeding is also slower, more laborious and difficult than sea spurge weeding. Marram Grass weeding involves spraying, wiping of individual leaves with herbicide or digging out entire clumps. In recent seasons, improved training in Marram Grass identification and the use of the monocotyledon specific herbicides has resulted in a significant increase in the rate of Marram Grass removal.
Stakeholders and Funding bodies: The SPRATS program has been supported by theTasmanian Parks and Wildlife Service, WildCare, and in the early part of the project, the Australian government’s Caring for Country program.
Contact information: Jon Marsden-Smedley, SPRATS (M) 0456 992 201 (E) jon.marsdensmedley@gmail.com / sprats.tas@gmail.com
EMR Project Summaries 