Category: Research & Science

Beneath the surface of Australia’s most important rivers and lakes, an ecological crisis is unfolding that receives far less public attention than the feral cat or cane toad, yet may be equally devastating to the long-term health of the continent’s freshwater ecosystems. The European carp (Cyprinus carpio), a large freshwater fish native to Europe and Asia, has become the most abundant and widespread invasive fish species in Australia, dominating waterways across the Murray-Darling Basin and threatening the survival of native aquatic species. In some stretches of river, carp now make up more than 90 per cent of the total fish biomass, earning them the grim distinction of being Australia’s most pervasive aquatic pest.

History of Introduction

Carp were first brought to Australia in the mid-nineteenth century, with early introductions occurring in Victoria, New South Wales, and Tasmania. For much of the following century, carp populations remained relatively small and localised, contained by natural barriers and limited connectivity between waterways. However, the situation changed dramatically in the 1960s when a particularly vigorous strain of carp, known as the Boolarra strain, was introduced to a farm dam near Boolarra in Victoria.

During major flooding in 1974, carp from the Boolarra strain escaped into the Murray-Darling river system, Australia’s most extensive and economically important network of rivers and streams. The combination of the Boolarra strain’s rapid growth rate, high fecundity, and the extensive connectivity of the Murray-Darling system created the conditions for an explosive population expansion. Within two decades, carp had colonised the entire Murray-Darling Basin, establishing themselves as the dominant fish species across a catchment area of more than one million square kilometres.

Biology and Reproduction

European carp are robust, long-lived fish that can grow to over one metre in length and weigh more than 20 kilograms in Australian conditions. They are highly adaptable, tolerating a wide range of water temperatures, salinity levels, and dissolved oxygen concentrations that would be lethal to many native fish species. This physiological versatility allows carp to thrive in degraded waterways where native species struggle, giving them a significant competitive advantage in many Australian environments.

The reproductive capacity of carp is staggering. A single adult female can produce between 100,000 and 1.5 million eggs per spawning event, and carp may spawn multiple times during a single breeding season when conditions are favourable. Spawning is typically triggered by rising water temperatures and increased water levels, such as those associated with spring flooding. This means that environmental flows and natural flood events, which are critical for the reproduction of many native fish species, can also stimulate mass spawning events in carp populations, further tilting the competitive balance in favour of the invader.

Environmental Impacts

The environmental damage caused by carp is extensive and pervasive. Carp are benthic feeders, meaning they feed by rooting through the bottom sediments of rivers, lakes, and wetlands in search of invertebrates, plant material, and organic detritus. This feeding behaviour stirs up sediment, increasing water turbidity and reducing the amount of light that penetrates the water column. Increased turbidity suppresses the growth of aquatic plants, which provide critical habitat and food sources for native fish, waterbirds, and invertebrates.

By uprooting aquatic vegetation and disturbing bottom sediments, carp also release nutrients that can trigger algal blooms, including potentially toxic blooms of blue-green algae (cyanobacteria). These blooms can cause significant water quality problems, affecting drinking water supplies, recreational water use, and the health of aquatic ecosystems. Research by the CSIRO and the Murray-Darling Basin Authority has documented the contribution of carp to water quality degradation across the Basin.

The impact of carp on native fish populations is both direct and indirect. Carp compete with native species for food and habitat, and their modification of aquatic habitats creates conditions that favour other invasive species at the expense of natives. Native fish species such as the Murray cod, golden perch, and various species of small-bodied native fish have all been negatively affected by the presence of carp, although disentangling the effects of carp from those of other threatening processes such as river regulation and habitat loss remains a challenge for researchers.

The National Carp Control Plan

In 2016, the Australian Government announced the development of a National Carp Control Plan, with a focus on the potential release of cyprinid herpesvirus 3 (CyHV-3), commonly known as the carp herpes virus, as a biological control agent. The virus, which is specific to carp and does not affect native fish, mammals, birds, or other animals, was discovered to be highly lethal to European carp, with mortality rates exceeding 90 per cent in some laboratory trials.

The Fisheries Research and Development Corporation (FRDC) coordinated a comprehensive research programme to assess the feasibility, risks, and potential benefits of releasing the virus into Australian waterways. The research addressed a wide range of issues, including the likely efficacy of the virus in Australian conditions, the potential environmental impacts of a mass carp die-off, the risks of the virus affecting non-target species, and the economic costs and benefits of the programme.

One of the most significant concerns raised during the assessment process was the challenge of managing the cleanup of large numbers of dead fish following a virus release. A mass carp mortality event could potentially produce millions of tonnes of dead fish, which if not promptly removed, could cause severe water quality problems, trigger secondary ecological impacts, and generate significant public amenity issues. The logistical and financial challenges of managing such a cleanup event across the vast Murray-Darling Basin are considerable.

Conventional Control Methods

While the potential for biocontrol continues to be evaluated, a range of conventional methods are employed to manage carp populations in Australian waterways. Commercial fishing for carp is encouraged in some jurisdictions, and recreational carp fishing events, such as the annual “carpathon” competitions held in various rural towns, help to raise awareness of the carp problem while removing fish from the environment.

Physical exclusion measures, including carp screens and barriers at key locations such as irrigation offtakes and wetland inlets, are used to prevent carp from accessing sensitive habitats. These barriers can be particularly effective in protecting wetlands and nursery habitats that are critical for native fish reproduction. However, the cost of installing and maintaining carp barriers across the extensive network of waterways in the Murray-Darling Basin is substantial.

Targeted removal programmes using electrofishing, netting, and trapping are employed in priority areas to reduce carp densities and support the recovery of native fish populations. Research by the CSIRO and state fisheries agencies has demonstrated that intensive carp removal can lead to rapid improvements in water quality, aquatic vegetation, and native fish abundance in treated areas, providing proof-of-concept for the benefits of effective carp control.

Commercial Utilisation

Efforts to develop commercial uses for carp have explored a range of potential markets, including the processing of carp into fishmeal, fertiliser, and pet food. In some regions, carp are sold to ethnic food markets where they are valued as a food fish. More recently, innovative entrepreneurs have experimented with processing carp into high-quality fish oil supplements and organic garden fertilisers, seeking to create economic value from what is otherwise regarded purely as a pest species.

While these commercial uses help to offset the costs of carp removal, the volumes required to make a significant dent in the overall carp population far exceed current commercial demand. The development of viable commercial markets for carp products remains an ongoing challenge, but one that could provide a useful complement to other control strategies if scaled up appropriately.

A Long-Term Challenge

The European carp is likely to remain a dominant presence in Australian freshwater ecosystems for the foreseeable future. Eradication is not currently considered achievable, and even significant population reductions will require sustained investment in a combination of biological, physical, and community-based control methods. The health of Australia’s rivers, lakes, and wetlands — and the native species that depend on them — will depend on our ability to develop and implement effective, long-term strategies for managing this pervasive and damaging invasive fish.

The carp problem serves as yet another reminder of the enormous ecological costs that can result from the introduction of non-native species, and the importance of strong biosecurity measures in preventing future invasions. As Australia continues to grapple with the legacy of past introductions, the lessons learned from the carp experience must inform a more cautious and scientifically rigorous approach to the management of Australia’s precious freshwater environments.

Australia is home to the largest population of feral dromedary camels (Camelus dromedarius) in the world. Estimated at between 300,000 and over one million individuals, these imposing desert animals roam across approximately 3.3 million square kilometres of the Australian outback, spanning the arid and semi-arid regions of Western Australia, the Northern Territory, South Australia, and western Queensland. Originally imported as essential beasts of burden during the nineteenth century, Australia’s feral camels are now a significant environmental, cultural, and economic concern.

A History of Service

Camels were first brought to Australia in 1840, when a single animal was imported to assist with the exploration of the continent’s vast interior. Over the following decades, thousands more camels were imported from India, Afghanistan, and the Middle East, along with their handlers — the Afghan cameleers, or “Afghans” as they became known. These men and their camels played an indispensable role in opening up the Australian interior, transporting supplies, building the Overland Telegraph Line, and supporting the construction of railways across some of the most inhospitable terrain on Earth.

The camel’s extraordinary adaptation to arid conditions made it perfectly suited to the Australian outback. Capable of travelling long distances without water, carrying heavy loads, and thriving in extreme heat, camels were the backbone of transport and supply in inland Australia for more than half a century. At the peak of the camel transport era in the early twentieth century, an estimated 20,000 domesticated camels were working across the continent.

However, the advent of motorised transport in the 1920s and 1930s rapidly rendered the camel obsolete as a working animal. As trucks and railways replaced camel trains, thousands of camels were released into the wild or simply abandoned in the desert. These released animals, perfectly adapted to the harsh Australian interior, thrived and began to reproduce, forming the foundation of the feral population that exists today.

Population Growth and Range

Feral camel populations in Australia have the potential to double every eight to ten years under favourable conditions. With no natural predators in Australia and access to vast expanses of suitable habitat, the population grew steadily throughout the twentieth century. By the early 2000s, the feral camel population was estimated at approximately one million individuals, prompting growing concern among land managers, conservationists, and Indigenous communities.

Feral camels range across the central and western deserts of Australia, including the Simpson Desert, the Great Sandy Desert, the Gibson Desert, and the Tanami Desert. They are highly mobile animals, capable of travelling hundreds of kilometres in search of food and water, and their movements often bring them into contact with remote communities, pastoral properties, and environmentally sensitive areas.

Environmental Impacts

The environmental impact of feral camels is substantial and wide-ranging. As large herbivores, camels consume a diverse array of native plant species, including many that are culturally significant to Indigenous Australians and ecologically important for desert ecosystems. Camels can strip vegetation from areas surrounding waterholes and springs, degrading these critical water sources and reducing their availability to native wildlife and human communities.

During drought conditions, camels congregate around the few remaining water sources in large numbers, causing severe damage to the surrounding environment. They foul water supplies with their excrement, trample vegetation, and physically damage water infrastructure such as bores, tanks, and pipelines. In some cases, camels have been known to break into buildings and community water supplies in their desperate search for water, posing significant risks to human safety and community infrastructure.

Research conducted by the CSIRO has documented the impact of feral camels on native vegetation communities, including the degradation of mulga woodland, the destruction of desert oaks, and the suppression of native shrubs and grasses. By reducing vegetative cover, camels contribute to soil erosion and the loss of habitat for native animal species, further compounding the ecological damage caused by other feral herbivores such as rabbits, goats, and donkeys.

Cultural and Social Impacts

For Indigenous communities in central and western Australia, feral camels are more than an environmental nuisance — they are a direct threat to cultural heritage, food security, and quality of life. Camels damage sacred sites, destroy bush tucker plants that are important food and medicine sources, and degrade the waterholes and rock holes that have sustained Aboriginal communities for thousands of years.

The physical presence of large numbers of camels near remote communities also poses safety risks. Camels can be aggressive, particularly during the rutting season, and collisions between vehicles and camels on outback roads are a serious hazard. The damage to fences, water infrastructure, and buildings caused by feral camels imposes a significant financial burden on remote communities that often have limited resources to repair and maintain infrastructure.

The National Feral Camel Action Plan

In response to the growing camel problem, the Australian Government funded the National Feral Camel Action Plan, a coordinated management programme that operated from 2009 to 2013 with a budget of $19 million. The programme aimed to reduce the environmental and social impacts of feral camels through a combination of aerial and ground-based culling, mustering for commercial use, and the development of improved management strategies.

The programme achieved significant results, removing approximately 160,000 camels from the landscape during its four-year operation. Aerial culling, conducted from helicopters, proved to be the most cost-effective method for reducing camel numbers across the vast and remote areas where they are found. However, the programme also generated controversy, with animal welfare organisations raising concerns about the humaneness of aerial shooting and the ethical implications of large-scale culling operations.

Since the conclusion of the formal action plan, feral camel management has continued through a combination of state and territory government programmes, pastoral industry initiatives, and Indigenous land management activities. The Department of Climate Change, Energy, the Environment and Water continues to coordinate national policy on feral camel management and provides guidance and resources to land managers across the affected regions.

Commercial Utilisation

One innovative approach to managing feral camels has been the development of commercial industries based on feral camel products. Camel meat, marketed as a lean, sustainable protein source, is now exported to markets in the Middle East, Southeast Asia, and Europe. Camel milk, which is rich in vitamins and minerals and lower in fat than cow’s milk, has gained popularity as a niche health food product, and several small-scale camel dairy operations have been established in Australia.

The live export of feral camels to countries in the Middle East, where they are valued for racing, breeding, and cultural purposes, has also provided an economic incentive for mustering and removing camels from the wild. While the commercial camel industry remains relatively small, it represents a creative and potentially sustainable approach to reducing feral camel numbers while generating economic value for remote and Indigenous communities.

Climate Change Considerations

An emerging concern related to feral camels is their contribution to greenhouse gas emissions. Like all ruminant and pseudo-ruminant animals, camels produce methane as part of their digestive process. With a population of several hundred thousand animals, feral camels are estimated to produce a significant quantity of methane annually, contributing to Australia’s overall greenhouse gas emissions profile. The CSIRO has conducted research into the methane emissions of feral camels, and this issue adds another dimension to the case for effective population management.

Looking ahead, the management of feral camels in Australia will require a sustained and multifaceted approach that combines population control, commercial utilisation, community engagement, and ongoing research. The challenge is significant — the vast scale of the camel’s range, the remoteness of the landscape, and the logistical difficulties of managing a highly mobile species across millions of square kilometres all present formidable obstacles. However, with continued commitment from government, industry, and communities, it is possible to manage feral camel impacts and protect the environmental and cultural values of Australia’s arid interior for future generations.