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Thursday, 23 September 2021

Supporting native species by managing carp in local waterways

A program initiated by Wangaratta Landcare and Sustainability Inc (WLS Inc) has removed tonnes of carp from the lower Ovens River in the past six years.

The work has been delivered in partnership with the Department of Environment, Land, Water and Planning’s Arthur Rylah Institute for Environmental Research (ARI) and the North East Catchment Management Authority (CMA).

Long-time fisherman and member of WLS Inc, Kelvin Berry said since 2015, the program had helped to remove 16.95 tonnes of carp from local rivers, wetlands and private dams.

“I believe this work allows the native fish to get a foothold back into their natural habitat, giving them a fighting chance to beat this enemy in our waterways,” Mr Berry said.

ARI regularly performs electrofishing surveys to monitor the populations of invasive and native fish species in Victorian waterways. Volunteers from WLS Inc maximise the time ARI staff can spend undertaking the surveys by assisting with logistics and organisation.

Carp found during the surveys are collected and transported to NutriSoil where they are converted into fertiliser which is sold commercially. The collaborative targeted approach maximises cost benefits of electrofishing and removes large quantities of carp from the catchment.

ARI Scientist Dr Scott Raymond, said maintaining long-term collaborative relationships with anglers, Landcare groups and citizen scientists is vital to conserving Victoria’s biodiversity.

The Lower Ovens River floodplain is recognised as a nationally important wetland complex containing 1800 individual wetlands, including at least 185 native and nine recorded endangered species. The ongoing work to protect and improve the area requires management of invasive species like carp.

Carp are such an issue because they are ecosystem engineers; they change their environment to suit them.

“Carp adversely impact freshwater systems through direct competition with native aquatic fauna for limited resources (e.g. food and shelter) and indirectly by suppressing the growth of aquatic plants,” Dr Raymond said.

When carp feed they suck mud and silt into their mouths and expel it through their gills, reducing water clarity and blocking the sunlight plants need to photosynthesise and grow.

Removal of mud/silt also destabilises stream banks, destroys habitat and reduces the soil seed bank damaging the ecosystems long term ability to rebound. Through habitat destruction, predation of fish eggs and direct competition throughout all life stages, carp can devastate native fish populations. 

Managing carp requires a continual effort due to their ability to breed and spread rapidly, especially during floods. Carp reach maturity in one to two years, can spawn three or four times per year and are capable of spawning greater than 100,000 eggs per kilo of body mass.

Healthy populations of native fish species can manage carp populations through competition and predation. Efforts to support native fish in the Ovens River include waterway improvements such as in-stream habitat reinstatement; fish barrier removal; and riparian restoration such as fencing waterways, vegetation re-establishment, responsible grazing and weed removal. 

“Before the recent rain, electrofishing results from sites on the Ovens River showed promising results with very few juvenile carp, we will see natives’ ability to maintain those low numbers during the next electrofishing survey,” Mr Berry said.

WLS Inc has acknowledged the time and effort by landowners and volunteers in assisting the restoration and management of local catchments.

The project is supported by North East CMA, Arthur Rylah Institute and Mulwala Water Skiing Club, with funding from the Victorian Government and the Department of Environment, Land, Water and Planning.

Picture: Wangaratta Landcare and Sustainability Inc members Tony Lane, Ian Minns and Kelvin Berry at Mullinmur Wetlands in Wangaratta on the Lower Ovens River which has been a focus of a carp removal project. Picture: Manifeasto Photography.

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