Tasmania in Action: Case Studies for Conservation Learning

Eradication of common carp from lakes Crescent and Sorell, Tasmania

Largest lake system globally from which common carp have been successfully eradicated

Case study learning summary

The Tasmanian Inland Fisheries Service (IFS) Carp Management Program achieved the world's largest successful carp eradication from Lakes Sorell and Crescent, protecting endemic species including the endangered golden galaxias and Ramsar-listed wetlands. Over 28 years (1995-2023), the program pioneered innovative techniques including "Judas carp" radio-telemetry, strategic spawning barriers, and integrated physical removal methods, demonstrating that eradication of established invasive fish populations is achievable in large natural systems where conventional methods like drainage or whole-lake poisoning are infeasible.

The program's success depended on immediate containment and rapid response, sustained bipartisan political commitment with dedicated funding, adaptive management responding to biological and environmental challenges, and effective multi-agency coordination with community support. This case exemplifies evidence-based adaptive management principles essential for protected area practitioners, validating that early detection, persistent monitoring, stakeholder engagement, and integrated threat management can address landscape-scale conservation challenges while maintaining ecosystem integrity and demonstrating measurable conservation outcomes.

Introducing the Tasmanian Carp Management Program

The Tasmanian Carp Management Program summary video, released in 2020 before eradication was confirmed.

Credit Inland Fisheries Service (IFS)

What and why

Purpose and drivers

Lakes Sorell (≈54 km²) and Crescent (≈23 km²) in Tasmania’s Central Plateau are ecologically and economically significant freshwater systems. They harbor unique endemic species (e.g. the endangered golden galaxias, Galaxias auratus) and support important recreational fisheries and water supplies (Wisniewski et al. 2015). Invasion by common carp (Cyprinus carpio) threatened these natural values, the Ramsar-listed wetlands of Interlaken reserve, and local industries.

Carp are highly invasive, rapidly breeding fish known to degrade water quality and habitat. Their presence in these lakes, first confirmed in 1995, posed a serious risk of spreading throughout Tasmania’s rivers, with potentially severe environmental and economic impacts (Wisniewski et al. 2015, Yick et al. 2021). The urgent driver for action was to protect Tasmania’s aquatic biodiversity and prevent the state-wide establishment of this destructive pest.

The challenge

Eradicating carp from large, open lakes was an unprecedented challenge. The lakes are shallow with extensive marshes, providing abundant carp spawning habitat (Wisniewski et al. 2015). Common carp have high fecundity and adaptable behaviour, making them difficult to eliminate once established (Yick et al. 2021). Furthermore, Lake Sorell’s larger size and diverse habitats (rocky shores, wetlands, deep areas) complicated removal efforts (Marshell 2023; Wisniewski et al. 2015). Conventional eradication methods like complete drainage or whole-lake poisoning were deemed infeasible – draining was impossible due to the lakes’ broad, flat basins and the need to maintain downstream water supply, and chemical poisoning (rotenone) was logistically very difficult, costly (~US$4.8 million), and would have caused unacceptable collateral damage to non-target species and water uses (Wisniewski et al. 2015). The challenge was to functionally eradicate carp without harming the lakes’ ecology or utility, and to do so in a setting much larger than any successful invasive fish eradication to date (Wisniewski et al. 2015). This required developing new techniques and maintaining intense, long-term effort despite the cryptic nature of aquatic invaders and difficulty of detecting low-density populations (Yick et al. 2021).

Objectives

From the outset, the Carp Management Program (CMP) established clear objectives to guide the eradication initiative (Wisniewski et al. 2015):

Containment: Prevent carp from escaping the Lake Sorell–Crescent system and entering other waterways.
Population Reduction and Eradication: Aggressively “fish down” the existing carp populations and ultimately eradicate carp from both lakes (Wisniewski et al. 2015). This was the ultimate conservation goal.
Prevent New Introductions: Stop any human-mediated movement of carp within Tasmania.
Protect Values and Safety: While pursuing eradication, protect the lakes’ native flora and fauna (e.g. avoid harming endangered species) and maintain essential services (e.g. continued domestic water supply) (Wisniewski et al. 2015).
Support and Knowledge: Implement supporting measures (public communication, tourism management, legislation and improve understanding of carp biology in these lakes (Wisniewski et al. 2015).

Collectively, these objectives reflect an integrated approach: contain the threat, eliminate it, and safeguard against any future incursions, all while balancing ecological, social, and economic considerations.

Where

The project focused on Lake Crescent and Lake Sorell.

Lakes Crescent and Sorell are internationally recognised Ramsar wetlands known for high biodiversity, extensive wetlands, and endemic species, such as the native golden galaxias (Galaxias auratus), the endangered southern bell frog, freshwater snails (Austropyrgus spp.), platypus, and water rats. Protecting these values made it especially crucial to eradicate carp. (Diggle et al. 2012)

Map of lakes Sorell and Crescent (Adopted from Yick et al. 2021)

How: Process and actions taken

Principles and strategy

The CMP adopted an adaptive, integrated pest management strategy focused on physical removal of carp combined with recruitment suppression and stringent biosecurity. After evaluating options the chosen strategy was to “physically fish down” the carp population through intensive netting and electrofishing, while simultaneously preventing carp from breeding or dispersing, crucial to outpace the carp’s reproduction (Wisniewski et al. 2015, Yick et al. 2021).

The program was highly adaptive, and tactics evolved over time as knowledge of carp behaviour improved and population densities fell (Wisniewski et al. 2015, Yick et al. 2021), exploiting carp vulnerabilities (such as their tendency to aggregate for spawning) at every life stage (Wisniewski et al. 2015).

Initial rapid response (1995)

On discovery of carp in Lake Crescent in January 1995, authorities moved swiftly. Within days, the lake’s outflow was shut and a fine 1 mm mesh screen installed to prevent downstream escape, and the lake was completely closed to the public (Wisniewski et al. 2015). Similar containment was applied to Lake Sorell immediately after carp were confirmed there in March 1995 (Wisniewski et al. 2015). These urgent actions effectively isolated the two lakes and confined the infestation to a single controlled system.

At the same time, emergency monitoring and removal began, with intensive surveys in both lakes and connected waters indicating a need to focus on Lake Crescent (Yick et al. 2021). A multi-agency Carp Working Group was established, led by the IFS and including inter-state fisheries departments, local government, water authorities and angling representative. Funds were committed to the eradication effort. (Wisniewski et al. 2015). The immediate mobilisation of personnel and equipment at this early stage proved critical to later success (Wisniewski et al. 2015).

Containment and fishing-down phase

During the late 1990s, efforts focused on aggressively reducing carp numbers (especially in Lake Crescent) and gathering biological information (Wisniewski et al. 2015). At first, tactics were basic – targeting visible aggregations of carp or likely habitats based on trial-and-error.

Crucially, catches and observations indicated that carp had not spread beyond the lakes into other rivers (Yick et al. 2021) which allowed managers to concentrate resources without worrying about satellite populations.

As knowledge grew, the CMP adopted a more targeted approach, pioneering the use of “Judas fish” – live carp fitted with radio transmitters – to locate remaining schools of carp (Wisniewski et al. 2015). By following these tagged individuals, the team could find other carp, map seasonal movement patterns, and identify favoured habitats (e.g. shallow marshy bays used for spawning) (Wisniewski et al. 2015). The program continually refined its methods – adjusting mesh sizes, net placement, and timing – to maximise catches as carp became scarcer and more skittish (Wisniewski et al. 2015). Population estimation via mark-recapture was also implemented to gauge progress and catch efficiency (Wisniewski et al. 2015), allowing the team to model how many carp remained and how much effort was still required.

Preventing reproduction

As the campaign shifted from control to pursuing full eradication, stopping carp spawning events became paramount. In the early 2000s the CMP developed physical methods to sabotage carp breeding using wire fences. This way, the carp’s own spawning drive was used against them – the fish would swim along the barrier until they hit a trap. Eggs or larvae that might be laid in any accessible vegetation were targeted with localised chemical treatments (Wisniewski et al. 2015). These measures dramatically reduced successful recruitment of new carp year classes.

Despite best efforts, the possibility of some spawning remained, so the team also prepared for contingencies. Throughout the 12-year campaign on Lake Crescent, this adaptive combination of containment, removal, and recruitment suppression steadily drove the carp population downward (Yick et al. 2021).

Setbacks and adjustments

Eradication efforts do not always progress linearly. A major setback occurred in 2009 when Lake Crescent had been cleared of carp but extremely wet conditions in 2009 caused Lake Sorell’s water level to rise substantially, flooding extensive marsh areas (Wisniewski et al. 2015). Carp accessed a spawning area that had been left unprotected due to limited netting resources and jumping over the barrier net in desperation (at the time, effort was still split between two lakes) (Wisniewski et al. 2015). The result was a large spawning event that set back the timeline for eradication (Wisniewski et al. 2015).

In response, the program rapidly recalibrated: additional funds were secured and this renewed effort successfully prevented any further significant spawning (despite high lake levels in subsequent seasons) and continually thinned out the remaining 2009 cohort (Wisniewski et al. 2015). By 2020 catches in Lake Sorell had dwindled to only a handful of aging individuals per year.

Monitoring and verification

Declaring functional eradication required high confidence that carp were controlled. Even after no carp were being caught in Lake Crescent, the team continued several years of monitoring with various methods to be certain the lake was clear of carp (Yick et al. 2021).

Significant events and timeline

Key players

The program's success was a team effort across government, scientists, and community. The IFS CMP provided day-to-day operational excellence, backed by strong governmental will and informed by scientific guidance, all with the community’s support.

Inland Fisheries Service

IFS Tasmania led the Carp Management Program, providing overall project leadership, on-ground expertise, and coordination. The dedicated CMP field team (initially four full-time staff) carried out most of the field operations year-round (Wisniewski et al. 2015).

Tasmanian government

The state government was instrumental, supplying emergency funding in 1995 and sustained financial support thereafter (Wisniewski et al. 2015) which created a supportive policy environment. Notably, a bipartisan political commitment ensured funding “for the life of the program” (Wisniewski et al. 2015).

Multi-agency taskforce

Image design by sentavio / Freepik

This included the Parks and Wildlife Service (for ecological and protected area input), the Rivers and Water Supply Commission and local Clyde Water Trust (to manage water level decisions and ensure downstream users’ needs were met (Wisniewski et al. 2015)), the Central Highlands Council (local government facilitating community liaison), and the Institute for Marine and Antarctic Studies / University of Tasmania and CSIRO scientists for research support. The Freshwater Anglers Council of Tasmania represented recreational fishers on the taskforce (Wisniewski et al. 2015), ensuring the angling community was informed and supportive.

Researchers and experts

Scientists played a key role in providing expertise and evaluating techniques.

Community and volunteers

The local community and anglers, while initially impacted by lake closures, became allies in the fight against carp.

Image: Former IFS Director John Diggle, former Minster for IFS The Hon. Guy Barnett and Mayor of Central Highlands Council Deirdre Flint marking the re-opening of Lake Sorell. Inland Fisheries Service

Achievements and supporting evidence

The project's adaptive strategy proved highly successful. Carp numbers dramatically reduced, with Lake Crescent declared carp-free in 2007 and Lake Sorell declared functionally eradicated in 2023.

Complete eradication in Lake Crescent

The most tangible achievement was the eradication of common carp from Lake Crescent. After 12 years of concerted effort (1995–2007), the last carp was removed in 2007 (Wisniewski et al. 2015). This restoration saved a vulnerable ecosystem – the lake’s native species and Ramsar-listed wetlands were secured from the carp’s destructive impacts. Notably, eradication was achieved, largely by physical removal with limited use of localised chemical treatment and while maintaining the lake’s ecological integrity and usage.

Former Carp Management Program leader Chris Wisniewski holding the last carp caught out of Lake Crescent. Photo: IFS

Functional eradication in Lake Sorell

Carp have now also been functionally eradicated from Lake Sorell, albeit over a longer timeframe. This marks the complete removal of common carp from all Tasmanian water bodies – an outcome of enormous significance for the state’s freshwater biodiversity. The once carp-infested Lakes Sorell and Crescent can now be managed for conservation and recreational fisheries without the looming threat of carp.

Current Carp Management Program leader Jonah Yick holding the last carp caught out of Lake Sorell. Photo: IFS

Containment

A critical achievement of the program is that carp were contained to the two connected lakes from the moment of discovery, despite the open hydrological connection to the River Clyde and Derwent catchments (Yick et al. 2021). This containment prevented what could have been a carp invasion of Tasmania’s river systems and other lakes. Tasmania remains one of the few regions in Australia still not plagued by widespread carp, thanks to this program.

Instalment of physical barriers prevented carp from moving into Tasmania’s river systems. Photo: IFS

Preservation of native species and ecosystem health

By removing carp, the program protected the habitat of numerous native species. The endangered golden galaxias fish, which exists only in Lakes Sorell and Crescent, was under extreme threat from carp through competition, egg predation and vegetation destruction. Waterbirds, frogs, and aquatic plants, have also benefited from the removal of carp (Wisniewski et al. 2015). By responding quickly to the threat, any negative effect of carp on native species and ecosystem health was prevented.

Additionally, maintaining downstream water supply was an achievement – the physical removal strategy kept the lakes’ ecological communities intact throughout the process.

Endangered Golden galaxias (Galaxias auratus), found only in Lakes Sorell and Crescent. Photo: IFS

Innovation and knowledge gain

The CMP yielded valuable scientific insights and new eradication tools. It demonstrated novel techniques (radio-tagged Judas fish, permanent spawning barriers) that can be applied to invasive fish control elsewhere (Wisniewski et al. 2015). The program also published an award winning peer-reviewed journal article "Eradication of the invasive common carp, Cyprinus carpio from a large lake: lessons and insights from the Tasmanian experience", as well as a comprehensive manual for carp control and numerous other internal publications documenting methods and results. These resources contribute globally to invasive species management literature.

Global significance

The eradication of carp from Lakes Sorell and Crescent stands as a globally significant achievement in invasive species management. To the best of available knowledge, this is the largest lake system in the world from which common carp have been successfully eradicated (Marshell 2023).

In summary, the CMP met its objectives: carp were contained and ultimately removed, native ecosystems were safeguarded, and invaluable experience was gained. As one report noted, the state-wide eradication of carp from Tasmania is an “outstanding, rare achievement on a global scale” (Marshell 2023), leaving a legacy of a carp-free Tasmania.

Factors affecting performance

Enablers for success

The eradication succeeded not by luck alone, but because of a confluence of enabling factors: rapid containment, strong and lasting support, the right people and tools, and an adaptive strategy underpinned by science and collaboration. It is a model example of how to create conditions in which an invasive species eradication can indeed succeed (Wisniewski et al. 2015). Several factors were pivotal in enabling the successful eradication (these are further explored in Section 7):

Early detection and rapid response
Strong political will and funding commitment
Containment and geographic advantage
Dedicated, adaptive team
Multi-agency collaboration and community support
Scientific guidance and learning
Sustained effort and patience

Barriers and challenges

While ultimately overcome, the program faced significant barriers and challenges:

Biological and ecological challenges

Common carp’s biology posed a constant hurdle due to their high reproductive capacity and ability to lay thousands of eggs in shallow vegetated water (Yick et al. 2021).

Scale and habitat complexity

The sheer size of Lake Sorell (≈54 km²) with its mosaic of habitats (open water, rocky areas, extensive wetlands) created significant challenges (Marshell 2023; Wisniewski et al. 2015).

Resource limitations at critical junctures

Although overall funding was strong, there were moments when resources were insufficient to cover all bases, for example in 2009 effort was split between maintaining Lake Crescent’s security and re-focusing effort in Lake Sorell. There were not enough barrier nets to simultaneously cover every inch of spawning habitat in both lakes (Wisniewski et al. 2015). This forced a tactical compromise that potentially contributed to the biggest setback of the program (a major spawning in Sorell) (Wisniewski et al. 2015).

Duration and sustained commitment

The lengthy timeframe was a challenge in itself. Keeping the political and public support engaged over decades was not easy and required ongoing demonstration of progress to justify the effort and expense.

Environmental variability

Unpredictable environmental factors sometimes hampered efforts. For instance, sudden floods (like in 2009) could disrupt planned operations or render some techniques less effective. While these factors can sometimes aid (drought was an ally mid-2000s), they also introduced uncertainty that the team had to constantly adapt to.

Multi-use water body conflicts

The lakes were not in a vacuum – they had other uses and values that needed consideration. Balancing the need to close lakes with pressure to reopen them for recreation, were social/political challenges the program navigated.

Overall, these challenges required the CMP to be resilient and adaptable. The toughest barrier – ensuring the rate of removal exceeded the rate of increase at all densities – was met through enormous effort and the prevention of spawning. This was achieved through the ability to adapt to changing conditions, continued improvement/development and evolution of effective gears and techniques, and some favourable conditions, but it was indeed “the most difficult criterion to meet” (Wisniewski et al. 2015). By recognising and addressing each barrier (often turning them into learning opportunities), the program managed to push through to success.

Key messages for success

Perhaps the biggest lesson is one of optimism: even notoriously invasive fish like carp can be eradicated from large natural ecosystems. This case met all the classical criteria for eradication success – zero immigration, all individuals susceptible to capture, reproduction rate surpassed by removal rate, persistent monitoring at low densities, cost-benefit in favour, and strong socio-political support (Wisniewski et al. 2015) – and thereby achieved its goal.

Although Lakes Crescent and Sorell are not formally protected areas, the CMP provides profound lessons in governance, adaptive management, ecological integration, stakeholder engagement, monitoring, and landscape-scale conservation—key competencies vital to successful protected area management in Tasmania and globally.

Early detection and rapid response

The immediate action taken following carp detection in Tasmania prevented a larger-scale ecological crisis. Similarly, protected areas require robust early-warning systems and preparedness to swiftly respond to invasive species threats, minimizing ecological damage. The value of an emergency response mindset (including securing political buy-in and funding very quickly) cannot be overstated (Wisniewski et al. 2015).

Adaptive management and innovation

Protected area managers need to embrace adaptive management principles to respond dynamically to evolving ecological conditions and emerging threats. A flexible, learning-driven approach enhances long-term conservation effectiveness. No single tool or “silver bullet” could eradicate the carp – it required a toolbox of methods used in concert (Yick et al. 2021). The program’s adaptability – continuously refining tactics based on monitoring data and carp behaviour – was crucial in overcoming hurdles (Yick et al. 2021). Rigidity would have likely led to failure; instead, an experimental, learning-by-doing approach ensured continuous improvement.

Further, in any multi-site eradication, prioritisation is key – tackling easier or higher-priority sites first, then concentrating efforts, rather than spreading resources too thin.

Sustained commitment, leadership and investment

Effective protected area management often requires sustained financial and political commitment to achieve meaningful long-term conservation outcomes, especially for complex problems like invasive species management or habitat restoration.

The long-term funding and political support provided by the Tasmanian government underpinned the carp eradication’s success. Protected area managers must similarly ensure sustained commitment and resourcing for ambitious conservation goals.

Ensuring flexible funding to address unexpected needs (like buying more barrier nets after the 2009 spawning event). Having contingency capacity can spell the difference between quickly mitigating a setback versus suffering long delays.

Cross-agency coordination and clear governance

Effective biodiversity management, whether within formal protected areas or conservation landscapes, requires clear institutional arrangements, cooperation across multiple stakeholders, and well-defined roles and responsibilities.

Integrated ecosystem and threat management

Protected area managers must integrate species-specific actions (e.g., invasive species eradication) with broader ecological goals, like maintaining ecosystem integrity and supporting species recovery.

The CMP not only eradicated carp but also indirectly supported the protection and recovery of native species, such as the golden galaxias, southern bell frogs, and platypus. Recognizing ecosystem-level impacts and addressing the invasive threat holistically ensured overall ecological resilience.

Studying your target and tailoring tactics to its habits can greatly enhance control efficacy. General methods are a starting point, but site-specific and species-specific patterns should guide smart deployment of effort.

Landscape-scale conservation

Effective protected area management increasingly recognizes the need for managing threats at a landscape scale rather than solely within isolated protected-area boundaries. This includes managing connected water catchments or contiguous habitats outside formally protected zones.

Rigorous monitoring and evidence-based decisions

Reliable monitoring data and evidence-based management decisions underpin effective protected area governance. The ability to demonstrate clear ecological outcomes is critical for ongoing stakeholder support and resource justification.

The CMP utilised sophisticated monitoring techniques—mark-recapture studies, biotelemetry—to track effectiveness and confirm outcomes. Such rigorously evidenced methodologies are directly applicable to protected area management in assessing the effectiveness of conservation interventions.

The CMP continued monitoring Lake Crescent for several years after the last catch to be absolutely sure no carp remained (Yick et al. 2021). Invasive species programs should plan for a dedicated confirmation phase with rigorous surveys (and new tools like eDNA) to distinguish true absence from non-detection (Furlan et al., 2019). Only with such evidence should eradication be declared. This patience in verification cements the success and avoids the pitfall of false success declarations.

Stakeholder engagement and community support

Successful protected area management depends significantly on building robust community support, fostering local stewardship, and engaging stakeholders proactively in decision-making and management actions.

Transparent communication about why extreme measures (like closing lakes) are necessary, and sharing success milestones, helps maintain public support and compliance.

Document and share what you learn

The team’s experience has been codified in manuals and publications, meaning the knowledge gained will help others.

Treating an eradication program not just as pest control but as an opportunity to advance science and methodology. Future invasive species eradications (whether fish or other taxa) can draw on the principles demonstrated here: early action, integration of tools, perseverance, and adaptation are the key ingredients for success.

Acknowledgements

This case study and its contents were researched and compiled by Our Common Place, formerly Conservation Management and developed with permission and generous input from Inland Fisheries Service. Thank you to the staff, past and present, who contributed insights, expertise and publications to this resource.

In particular, we acknowledge retired IFS Director John Diggle and retired former Carp Management Program Leader Chris Wisniewski, whose dedication and passion for the cause were pivotal to the program’s success. We also make special mention to the late Senior Technical Officer Paul Donkers, whose leadership and knowledge were invaluable to all staff involved in the CMP.

Video production was provided by the University of Tasmania. Special thanks are extended to Matthew McKee, Educational Technologist Sciences and Engineering, Academic Division for his generous input of time and skill.

Banner image: Common carp (Cyprinus carpio). Photo credit Inland Fisheries Service

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