Carp (Cyprinus carpio) originated in central Asia and spread throughout Asia and Europe as an ornamental and aquaculture species.  Carp were released into the wild in Australia on a number of occasions in the 1800s and 1900s but did not become widespread until a release of 'Boolara' strain carp from a fish farm in the Murray River near Mildura in 1964.  The spread of carp throughout the Murray-Darling Basin coincided with widespread flooding in the early 1970s, but carp were also introduced to new localities, possibly through their use as bait.

Introduced carp are now the most abundant large freshwater fish in the Murray-Darling Basin and are the dominant species in many fish communities in south-eastern Australia.

Distribution

Carp are found in all Australian states and is the dominant species of the Murray-Darling Basin.  Carp are commonly found to be from 50 g to 5 kg in weight and can tolerate a range of water temperatures, salinity levels and polluted water.

A survey of fish abundance in Australian rivers by Driver (2003) found that inland rivers had higher carp densities than coastal rivers.   Carp were found in all inland sites below an altitude of 500 m above sea level.   Higher carp densities were associated with riverine systems exhibiting human impacts, most notably, the effects of dams and agriculture.  Alteration of flows and water temperatures, physical barriers to fish migration, carp spawning habitat created in artificial lakes and agricultural effects on water quality were all linked to higher carp biomass densities (Driver 2003).

Carp ecology

There are about 10 different strains of carp in the Murray-Darling Basin.

Carp larvae can’t swim, they only drift with river flows.  In two years of research, no carp larvae have been found drifting in the Murray River upstream of Barmah-Millewa Forest, only downstream – this indicates that carp do not spawn upstream of the Barmah-Millewa Forest.  As such, the Barmah-Millewa Forest is considered a ‘hot spot’ for carp breeding.  Other identified ‘hot spots’ in the Murray-Darling Basin include the Gwydir Wetlands, Namoi Wetlands, lower Warrego River and the lower Boomi River.

Research in South Australia indicates that carp are always the first fish into wetlands (when waters rise) but the last to leave. In some instances, carp have been seen still entering wetlands while native fish have long departed following a drop in water levels.

Carp rely very much on their sense of smell  as they usually operate in dark, murky waters.  Research on crucian carp and goldfish has shown that they produce pheromones which act as a chemical ‘smell’ and trigger certain behaviours.

Carp can pull twice their own weight and jump about one metre.  They also have a ‘pushing’ instinct, which has not been similarly seen in native fish.

Economic Impact

Carp can increase water turbidity and damage aquatic plants through their feeding behaviour, degrading aquatic systems and therefore detrimentally affecting values of wetlands.   It should be noted that there exists a lack of quantitative data on the impacts carp have on the environment.  Confounding factors, such as removal of riparian vegetation, watercourse alteration, and stock access to waterways, make it difficult to quantitatively assess carp damage. It is estimated that this species generates an annual cost impact of more than $15.8 million per year.

Table 1: Annual Cost Impact of Carp

Cost Component	Control $A million	Loss $A million	Total $A million
Management of carp (b)	2.00	--	2.00
Research cost (c)	2.00	--	2.00
Environmental impact (a)	--	11.80	11.80
TOTAL COST	4.00	11.80	15.80

(a):  Annual cost to community estimated in this assessment
(b):  Control costs for carp taken from Bomford and Hart (2002) and $1 million per year from the Tasmanian government for Crescent Lake
(c):  Public sector research costs for carp taken from Bomford and Hart (2002) and new projects.

Carp Management Costs

Bomford and Hart (2002) indicated that $2 million per year is spent by the public sector on carp management.  Somewhere in the order of $2 million was spent on research.  Farmers also complain about damage done to irrigation canals and water losses due to the digging behaviour of carp.  It is difficult to quantify these losses, but they may have some significance at a national level.

Environmental Impact

Carp generate environmental impact through causing increased water turbidity, reducing the abundance of invertebrates and aquatic plants and possibly displacing other fish species.

Environmental impacts generally result from the bottom-feeding behaviour of carp.  Sediment in inhaled and sifted through the gill rakers in an activity known as 'mumbling' and can increase turbidity, release sediment nutrients and destroy aquatic plants. In relation to generic water quality issues in Australia, Possingham et al. (2002) noted the annual cost of water turbidity to be $24 million and the cost of sedimentation to be $4 million per annum.  If carp contributed to 10% of this cost, then the impact of carp-related sedimentation and heightened water turbidity would be about $2.8 million per year.

The impacts of carp on native fish populations are not readily apparent (Harris, 1994).  Carp may make aquatic habitat less suitable for native fish breeding and survival, and provide competition for resources.

The greatest impact of carp is on the abundance of invertebrates and aquatic plants, which form the basis of native fish diets. There is evidence of competition - for example, a fish survey found that there was an average of only 2.6 native fish species per site in the Murray region, compared with 4.6 species in the Darling sites.  Carp were the main alien species contributing to the changes in the proportional abundance of native species.  Native species whose abundances were most reduced by river regulation were western carp gudgeons, bony herring, and striped gudgeons (Driver 2003). 

In some parts of Australia fishing has been banned as a result of carp presence.  Lake Cresent (Tasmania), for example, which has been counted as having around 1,500 full season anglers who exclusively fished the area has been closed in the lead-up to brown trout season.  Aside from directly affecting the well-being of these anglers, possible decreased expenditure by these people would have affected support industries.  Each freshwater angler is estimated to spend around $535 on the sport (Henry and Lyle 2003).

Households surveyed in America and Australia have indicated a willingness to pay for the restoration of wetlands and anglers were found to be willing to pay for prized species.  This ‘willingness to pay’ was as high as $80 per household per year in the USA.

For the purposes of valuing biodiversity in the 'Counting the Cost' report, it was assumed that each household would be ‘willing to pay’ $50 per year for improved fishing quality.  Households with fishers are most likely to benefit from being able to catch prized native species.  The size of the recreational fishing sector in Australia is substantial.  ABS (2002) estimated some 5 million Australians fishers, although participation rates vary considerable.  Only limited numbers of these fishers would use inland waters where carp are present.  A survey of fishing in NSW indicated that there were an estimated 998,501 recreational fishers in 2001.  Recreational fishing activity was greatest in estuarine waters (47% of total events).  Fishing in coastal waters (28% of events), freshwater rivers (15% of events) and lakes and dams (10% of events) followed in importance (NSW Fisheries 2002).

Given that somewhere in the order of 25% of fishers surveyed utilised inland waters, and many of the 5 million fishers in Australia would be irregular, it is estimated that there are around 0.6 million Australians who have regular contact with inland waters where carp could possibly be a problem.

Aggregating the ‘willingness to pay’ for improved fishing quality of $50 per household over 0.6 million fishers, the aggregate cost of decreased fishing quality was estimated to be $30 million per year.  This cost was derived on the basis, that in the absence of carp, fishers would have satisfactory water quality and greater abundance of native fish.  If carp were contributing to a 30% decline in prized fish species, then a social cost of $9 million per year could be attributed to the impact of carp on recreational fisheries.

A carp study in Gippsland pulled together the various costs associated with carp.  The study by the Gippsland Lakes and Catchment Action Group (1996) estimated the annual cost of carp on the native commercial fishery, losses to recreational fishing, impact on tourism and local commerce to be $35 million per year, although, the method for estimating these losses was not explained (Koehn et al. 2000).

Aggregating the turbidity and decline in recreational fisher value estimated in this analysis, generates an annual cost of $11.8 million per year.

Social Impact

The commercial harvesting of carp provides employment opportunities in rural and regional Australia.  For example, K and C Fisheries, the largest carp producer in Australia, processed 900 tonnes of carp in 1999.

The retail prices for whole carp can reach $7 per kilogram, however, much of the commercial catch is used for low-value products such as fertiliser (15 cents per kilogram) and crayfish bait (50 cents per kilogram).

There are approximately 70 licensed carp fishermen in Australia and the total gross value of the industry in 2002 was $A 1.7 million (Bell 2003).  There are a number of costs associated with carp production including harvesting costs: licences, nets, labour, vehicles, boats, issuance, QAP factors; storage costs: refrigeration plant and running costs, factory approved by govt/AQIS, QAP factors; marketing costs: transport, commission, handling unknown factors, chemical analysis; and packaging costs: cardboard boxes, plastic crates, ice slurry, plastic bags/liners, pallets (Bells 2003).

References

ABS (2002) Year Book Australia 2002 – Forestry and Fishing, AGPS, Canberra.
Bell, K. (2003) A review of the commercial use of carp, in Proceedings of the National Carp Control Workshop 5 – 6 March 2003, CSIRO Discovery Canberra, Pest Animal Control CRC.
Bomford, M. and Hart, Q. (2002) Non-indigenous vertebrates in Australia, in Pimentel, D. (ed.) Biological Invasions – Economic and Environmental Costs of Alien Plant Animal and Microbe Species, CRC Press.
Driver, P. (2003), Using large spatial scale models to understand where carp prosper in rivers of New South Wales, CRC Freshwater Ecology website
Driver, P., Harris, J. Norris, R. and Closs, G. (1997) The role of the natural environment and human impacts in determining biomass densities of common carp in New South Wales rivers. Cited in Gehrke. PC and Harris, JH. (eds.) Fish and Rivers in Stress: The NSW Rivers Survey, NSW Fisheries Office of Conservation and the Cooperative Research Centre for Freshwater Ecology, Cronulla.
Harris, J.H. (1994) Carp in Australia: the role of research in C. Nannestad (ed.) Proceedings of the Forum on European Carp, Wagga Wagga, NSW, 20 June 1994. Wagga Wagga, pp. 17-20.
Harris J., Gehrke, P. and Hartley, S. (1998) NSW Rivers Survey shows declining fish and degraded streams, Water May/June 1998.
Henry, G.W. and Lyle, J.M., (2003). The National Recreational and Indigenous Fishing Survey. Final Report to the Fisheries Research & Development Corporation and the Fisheries Action Program. Project No. 1999/158. NSW Fisheries Final Report Series No. 48. pp. 188.
Gippsland Lakes and Catchment Action Group (1996) Drawing the Line on Carp. Proposal for the Control of Carp in Gippsland Lake, Bairnsdale, Victoria.
Koehn, J.D., Brumley, A.R., and Gehrke, P.C. (2000), Managing the Impact of Carp, BRS, Canberra.
NSW Fisheries (2002) Survey of Recreational Fishing in New South Wales Interim Report, NSW Fisheries, December 2002.
Possingham, H, Ryan, S, Baxter, J and Morton, S (2002) Setting Biodiversity Priorities: paper prepared as part of the activities of the working group producing the report Sustaining our Natural Systems and Biodiversity
for the Prime Minister’s Science, Engineering and Innovation Council in 2002
Wilson G. R (1998) Opportunities and Constraints Upon Commercial Use of Carp in NSW, Industry Development Study for NSW State And Regional Development, Port Macquarie.