LAKE BONNEY TORTOISE RESCUE PROJECT

Graeme Hopkins – Registered Landscape Architect and Registered Architect, Director of Fifth Creek Studio

This project is a collaboration between Adelaide University’s Landscape Architecture student construction studio, local government authorities and Fifth Creek Studio. The Lake Bonney Recreation Study (Fifth Creek Studio for Berri Barmera Council, 2000) identified the local population of Murray River Tortoise (3 species) and only known habitat on the western shore of Lake Bonney as being in crisis, with an aging population and very few juveniles surviving. Predation of nests by foxes is unsustainable at 93% (Thompson, 1983) and uncontrolled vehicle and pedestrian access destroys the breeding habitat and remaining hatchlings. Through consultation with community and local authorities, and detailed site investigation, innovative designs were developed for fox proof fencing, reconstructed salt affected habitat, and interpretation for pedestrian access to the site. Significantly, this site is an indicator of the health and biodiversity of the broader Lower River Murray.

This paper, together with slides and a powerpoint presentation, was presented by Graeme Hopkins at the People + Places Conference 2002.

INTRODUCTION

There appears to be a crisis in the local population of Murray River Turtles (3 species: short neck, long neck and broad shell), with an aging population and very few or no juveniles surviving. The predation of nests by foxes is the major cause, at the unsustainable rate of 93% (Thompson, 1983). In addition, uncontrolled vehicle and pedestrian access destroys the breeding habitat and hatchlings.

Graeme Hopkins, Lecturer at Adelaide University, set up a Landscape Architecture studio for this site, which encompassed ecological research through to construction documentation for the protection of the habitat and interpretive infrastructure. Running in parallel to this is the responsibility of the Landscape Architect in the environmental management of a threatened species. Does this responsibility stop when the job is completed, ie when the fees run out?

WHERE IT IS

Lake Bonney is situated in the River Murray Basin at Barmera in the Riverland region of South Australia. The lake acts like a kidney (as its shape coincidentally resembles), absorbing pollutants and salts and holding them instead of releasing into the river system. Since the lock system was introduced to the River Murray, Lake Bonney has been a permanent water body.

HOW THE PROJECT STARTED

The Berri Barmera Council engaged Fifth Creek Studio (FCS) to undertake the Lake Bonney Recreation Study in 2000. In consultation with the Riverland Animal and Plant Control Board FCS identified that the local population of River Murray Tortoise (recently renamed Turtle) and its habitat is endangered. The dangers to the habitat and turtle population at Pelican Point on the western shore of Lake Bonney include unsustainable predation of nests by foxes and unrestricted vehicle access across the breeding area creating soil compaction, vegetation destruction and direct destruction of nests and eggs.

FCS documented this situation and made recommendations to address the problems in the Recreation Study. The Berri Barmera Council adopted the recommendations and made a commitment to their implementation over time.

As professionals, Landscape Architects have a responsibility to the environment, and after becoming aware of the plight of the turtles and their degraded habitat FCS felt that the situation warranted urgent attention. FCS therefore put together a proposal for habitat restoration, protection from predators, and visitor interpretation at Pelican Point and prepared a National Heritage Trust (NHT) grant application in early 2001. The Murray River Catchment Water Management Board and Berri Barmera LAP committee provided advice, and the application was supported by in-kind and capital funds commitments by The Berri Barmera Council. FCS secured the cooperation of Adelaide University’s Department of Environmental Biology and the School of Architecture, Landscape Architecture and Urban Design (where Graeme Hopkins lectures). Letters of support for the application were also provided by local schools, Waterwatch, Bookmark Biosphere, Australian Landscape Trust, neighbouring land owners and other members of the community.

This NHT application was unsuccessful. Undeterred, FCS pursued the project through Adelaide University connections. The Environmental Biology Department had offered to provide an Honours student to develop a set of environmental design criteria, which Landscape Architecture students under the leadership of Graeme Hopkins, would use to develop a safe breeding habitat. A setback occurred when the Honours student was taken off the project as he did not have the required science subjects. However Graeme Hopkins decided to continue the project via his Studio 1B, a construction oriented studio, with environmental biological input being provided by Associate Professor Keith Walker and other experts in the field. This will be discussed further later in this paper.

ISSUES

The turtles are not endangered in the River Murray Basin BUT are an endangered species at Lake Bonney (population profile). The reasons for this include:
· Predation of foxes
· Salt levels in Lake Bonney
· Habitat loss by human activities (4WD, land surfing on car bonnets, etc)

A scientific study of tortoises along the River Murray in South Australia, including at Lake Bonney, was undertaken by Michael B. Thompson of the Department of Zoology, The University of Adelaide, in the early 1980s. It was shown that 96% of eggs were predated in the nest, with only 3% of this total by endemic predators and the remaining 93% by foxes. This means that only 4% of eggs laid survive to the stage of juvenile tortoises. In other studies on the River Murray in Lake Hume (Spencer, Ricky-John, 2001) predation rates of 93% by foxes with a small proportion of nesting adult females being killed, is suggested. This has not been observed at Lake Bonney but evidence of adult shells have been found, suggesting this does occur as well.

The level of salt in the lake directly affects the function and usage of the lake. The higher the salt level, the less the aquatic plant life such as ribbon week that the turtles feed on. On the other hand the reduced aquatic vegetation provides for greater recreation usage for boating, skiing and so on, but also creating a dangerous environment for the turtles’ breeding habitat.

The vegetation was completely destroyed and removed during the mid nineties by an activity that is common in inland rural communities, land surfing on an old car bonnet. A bonnet is towed behind a 4WD and driven in large circles through the low saltbush and samphire vegetation. This flattens the plants and cover to the breeding area. Council constructed barriers to stop this activity because it was a danger to the nearby nudist beach. Since then the barriers have been removed by the 4WD land surfers, and 4WD access occurs for fishing and sightseeing. The vegetation has recovered and is growing back to its original density. Other human activities include the regular pedestrian movement along the water edge and associated dog activity that disturbs the habitat.

There are a number of factors affecting the habitat, and therefore habitat protection requires a multi faceted approach. Phil Reddy of the Riverland Animal and Plant Control Board has conducted experiments in fox baiting, with a good success rate. Three to four months after baiting he observed the first hatchlings reaching the lake from their sand nests that anyone has seen since the mid 1980s. Nesting takes place in spring, particularly after rain. It has been observed that hatching of juveniles occurs after rain and close to a full moon.
The fox is the major predator, as identified by previous studies (Thompson, 1983, Spencer, 2001). There appears to be an intense population in the surrounding area, given the ample food supply, such as rabbits and horticultural produce including grapes from nearby vineyards. Foxes are mobile animals and can travel considerable distances during the night. “Exceptional movements of over 300 kilometres have been recorded in North America and 100 kilometres in Europe [Corbet and Harris 1991]. Mean dispersal distances are much smaller than this, ranging from 2.8-43.5 kilometres for males and 1.8-38.6 kilometres for females [Trewhella et al. 1988]. In Australia, Coman et al. [1991] in central Victoria, observed a mean dispersal distance of 11 kilometres based on a study of 13 dispersing animals” (Saunders, Coman, Kinnear and Braysher, 1995, Managing Vertebrate Pests: Foxes). With this sort of movement baiting can only remove residential foxes, and new ones move into the area quickly to replace the baited animals.

Predation of nests by foxes appears to be behaviour which is learned from parents and not instinct. Phil Reddy has noted that once the breeding cycle of foxes is broken through baiting the next generation do not automatically know how to find the eggs. They need to be shown or to learn by chance.

A more long term solution than seasonal baiting is to construct a physical barrier or fence to exclude foxes, but allows turtles to move in and out of the area. Natural barriers such as water are effective barriers to foxes but not a complete answer, as foxes do swim. The fox is an opportunist feeder and would need a ready food source to temp them into swimming for their food.

A review of the effectiveness of exclusion fences for foxes (Coman and McCutchan, 1994) concluded that most of these fences provided a barrier to foxes but not a complete barrier. Coman and McCutchan suggest that a successful barrier is good fence maintenance and frequent monitoring for the presence of foxes. The review also concluded that exclusion fencing remains an important tool in the management of threatened or endangered species. Keeping foxes out is “difficult due to the agility of the animal…foxes can scale electrified fences” (Saunders et al, 1995, p.84).

There is a large range of exclusion (fox proof) fences and levels of effectiveness of these fences, starting with the simple wire-netting fence which is rarely effective regardless of height. Fences that incorporate a roof or overhand are more effective. Successful high netting fences with unstrained overhanging tops, such as at Warrawong Earth Sanctuary in South Australia, prevent foxes climbing over the floppy top part of the fence.

Electrified fences are effective if they are designed correctly, in particular the height of the electric wire and use of outriggers to deter the fox from using the electric shock to catapult over the fence. A popular solution is the combination of netting and electrified wires, which can be useful, but again the position of the electrified wires is critical. The down side of fencing an area is the effect it has on the overall ecology of the enclosed area. “Fences can interfere with the movement of non-target animals” (Saunders et al, 1995, p. 85).

CONSTRUCTION STUDIO

The construction studio is based on a studio learning process where the students work individually and collaboratively to find workable solutions to a series of landscape problems and scenarios. In 2002 Graeme Hopkins introduced the Lake Bonney Tortoise Rescue project into this semester long studio.

The project involved eight undergraduates, including one student on exchange from Canada and two Masters students from Vietnam. A four day field trip to Lake Bonney was organised for the first week of semester, with a project briefing by Graeme Hopkins and an introductory lecture on turtles by Associate Professor Keith Walker just before the students, with their bicycles, boarded the bus.

Cabin accommodation at Lake Bonney was provided by The Berri Barmera Council. Each morning the students cycled about 5 km to Pelican Point, through soft sand and clay silt, which tested their mountain bike skills. Examination of access to the area was an integral part of the project. At the site they conducted an intensive site survey, which included taking levels, documenting vegetation and observing other biophysical elements such as salt levels.

Because of the flatness of the site it was important to produce a detailed contour plan with contour intervals being close, such as 200 mm or so. If there are slight undulations or depressions they might have a major effect on the micro climate of that area, especially holding water, dew, etc. This area only receives 200 to 250 mm per year.

The vegetation survey and mapping of the vegetation profile of the dunal system was also an important task. When a cross section of the dune with its vegetation profile was overlaid with the estimated ground water table (taken from a series of nearby bore measurements for salt levels) a number of species was found to occur at certain water levels and salt levels. More work needs to be carried out to establish trends, but this knowledge would be helpful for future revegetation projects.

OBSERVATION OF BREEDING SITE THROUGH SITE ANALYSIS

As the lake has become a permanent water body, due to the river’s lock system, this has affected the water edge, with a steep drop off caused by wave action and the dense growth of water couch (Cynodon dactylon) forming a physical barrier of up to 300 mm high. It was discovered that turtle nests were opposite the water edge where it was a gentle slope, more like a beach. In other areas where wave erosion and water couch causes a physical barrier, no turtle nests were found, presumably because the barrier is too hard to negotiate.

A large proportion of nests were located at the base of a particular plant, a green samphire. This has been observed over a number of years by Phil Reddy, the Riverland Animal and Plant Control officer. Other scientists and ecologists have dismissed any connection between the plant and egg nesting. However, I am inclined to believe, with Phil Reddy, that there could be a connection to do with shading and softness of soil, and possibly the root structure and soil profile associated with this particular plant. It is possible for the green samphire to have a deep root system that taps into the ground water table, which provides extra leaf growth that shades the soil, thus being more friable to dig into for nesting. The green samphire is located in a particular zone on the low dune, indicating a preference for that micro climatic condition.

One option would be to excavate around one plant to expose the root structure to see what can be discovered. This has not been done yet. The importance of this is that, if there is a connection, then other degraded habitat sites in the Lower Murray could be revegetated in such a way that this species is given more opportunity for successful nesting.

The idea of managing the water couch, for instance by mowing or whipper-snipping prior to the nesting and hatching season, could be tried to reduce the physical barrier and widen the potential breeding site. Even the construction of low, wide, timber ramps over the water couch might provide easier access to the turtles.

STUDIO WORKSHOPS

In the afternoons, when temperatures on site soared, the students met for a series of workshops in the Council Chamber. Locals involved in conservation were invited to make presentations to the group and to participate in the workshops. These included representatives from the Animal and Plant Control Board, the LAP project officer and the land owner of the neighbouring property, currently run as a caravan and camping resort.
During the workshops it was learned that a second breeding habitat occurs about 100 m north of the current site at Pelican Point. It was decided that this area could be excluded from the proposed fenced area, to act as a control site for comparison with the fenced area. This way any differences in turtle behaviour and rates of hatchling survival can be monitored.

Current work being completed, but as yet unpublished, by a Geologist indicates that the lake is acting like a natural lake. It is suggested that the water has deposited enough silt to seal the lake bed, thus stopping the salt laden ground water entering the lake. This ground water is deflected away from the lake towards the river. This could also explain why there has been a drop in the lake salt levels over the last year or so.

Through the workshops it became clear that this site can be seen as a biological indicator for the general health of the lake and of the Lower Murray River:
· Salt levels can be observed through lake aquatic plant growth
· The breeding habitat vegetation responds directly to the salt level in the ground water in its growth habits
· The turtle hatchlings survival rate responds directly to the level of feral animals and human interference in the habitat.

Over the four days the students produced site plans detailing all existing vegetation and other features. This formed the basis of their project, to develop a fox proof fencing system capable of occasional inundation. They examined a range of options, such as the fencing style successfully used by Earth Sanctuaries. Other concepts were explored such as loose netting that discourages foxes climbing, and the use of plants with thorns etc that stick into foxes’ foot pads and cause discomfort. Observations have been made of foxes staying to dirt tracks instead of crossing country with prickly plants.

The students researched suitable plants and revegetation methods to protect the breeding habitat. They addressed other issues including interpretive infrastructure and signage. They looked at carparking location and design and provision of appropriate access for visitors via a pedestrian/cycle path to the site. The students had to develop a set of construction drawings for this project, to be completed and assessed 4 weeks after the field trip.

FUTURE FOR THE PROJECT

This project is ongoing, with Fifth Creek Studio investigating ways to raise the funds to develop the fencing. The Animal and Plant Control Board has made a commitment to monitor the site, collecting data on the hatchlings and survival rates, as compared to an unfenced control site nearby. Council has committed funds towards the carpark and vehicle barriers.

Out of this project eventually we may develop a set of guidelines useful for similar areas in the Lower Murray River.

BIOGRAPHICAL SUMMARY

Fifth Creek Studio – rural focused practice, specialising in intensive community consultation to develop innovative landscape and urban design.

Adelaide University – Landscape Architecture studio based course, with this project encompassing ecological research through to construction documentation of the habitat and facilities.

Graeme Hopkins – Registered Landscape Architect and Registered Architect, Director of Fifth Creek Studio and Lecturer in Landscape Architecture at Adelaide University.