Issue 94, 26 June 2003

Understanding the Biology of Carp in Victorian Waters

The common carp is found in freshwater and brackish water bodies throughout Victoria. It was probably first introduced into Australia during the 1860s and 1870s by members of acclimatisation-societies who wanted to recreate familiar Northern Hemisphere landscapes. Carp numbers in Australian waterways remained low for nearly a century. However after illegal stocking in waterways across south-eastern Victoria during the 1960-70s, carp numbers increased dramatically. Today, carp are the dominant fish species in many of Victoria's inland waterways.

High densities of carp are thought to cause habitat and water quality degradation, which may lead to the local exclusion and extinction of native freshwater fish populations. The late 20th Century saw renewed interest in carp that coincided with carp populations establishing in new areas of Tasmania and Victoria, including the Glenelg River catchment, Deep Lake and Lake Toolondo. By the end of the 1990s, agencies managing inland waterways identified the control of carp as a primary concern.

For a species that has inhabited our waterways for a little over 100 years, little was known about some of the most basic aspects of the biology and ecology of carp in the variety of freshwater environments it inhabits. For effective control measures to be successfully developed and undertaken, it is critical to know how feral populations of carp behave. So in 1999, Fisheries Victoria funded MAFRI to determine the key characteristics of carp populations in Victoria. The research team collected information from 5 locations, which represented the important habitat areas where carp are found in Victoria. These included a large Murray-Darling basin river and its associated wetlands, large lakes and reservoirs, irrigation channels, coastal freshwater/brackish lakes and coastal rivers and their associated wetlands.

The average age of carp sampled swimming in Victoria's waterways was 6 years for males and females. However, a major finding of the study is that very old fish (>25 years) exist in many populations including Gippsland Lakes, Murray River at Barmah, the Kerang Lakes and the Barwon River. The oldest carp caught in this study was 32 years old. This doubles the previously known longevity of 16 years. Some of the carp swimming in Victorian waters today are likely to have been part of the first generation of invaders that colonised these waters in the late 1960s and early 1970s.

The age structure of carp varied across populations. The study found some populations were faster growing and shorter lived (maximum age 17 years) while others were slower growing and longer lived (maximum age 28 years). The age at which carp sexually mature also varied considerably across populations. The age at which 95% of the females in a population reached sexual maturity ranged from just over 2.5 years old (from the Campaspe irrigation channel populations) to just over 4.5 years (Barmah wetland population).

Males generally matured earlier, with 95% of the population being sexually mature at just over one year old to just under 2.5 years of age (Barmah and Campaspe populations respectively).

The results of this study have also shown carp in Victorian waters have a long spawning period. Spawning generally peaks during Spring and early Summer but also occurs through until Autumn and can even start in late Winter at some locations. Spawning is triggered by rapid increases in water temperature. Most populations of carp contain females that spawn only once during a season as well as females that spawn repeatedly within one season. Females produce a lot of eggs each season and their egg producing potential is not a function of age but of their size - the weight of the fish. This means that the weight of females in the population will determine the number of eggs produced by that population. Two populations, with the same weight of mature female fish, but which may have vastly different age and sizestructures, will produce roughly the same quantities of eggs.

The egg production rates within and between each population are extremely variable. Carp populations in the Barwon River, Campaspe irrigation channels and Lake Modewarre were the most productive. The largest females in these populations produce over one million eggs per year.

Larger egg size is thought to provide an early survival edge for larval fishes and like egg production, this study found carp egg size was related to female size and weight. Female fish taken from Lake Modewarre produced the largest eggs documented in this study. The study also found that environmental factors such as floods, positively aided the survival of larval and juvenile fish. This was particularly evident in carp populations from wetland habitats. The abundance of juveniles was highest in years where significant floods occurred. However, analysis of the structure of the populations showed that even in the poorer years, when flooding did not occur or was minor, large numbers of larval and juvenile carp did survive to join the population.

The population biology data collected in this study are being used to assess the viability of strategies to control carp populations in Victorian waterways. For more information about this project please contact Mr Paul Brown at MAFRI on 03 5774 2208.

Goulburn River Enforcement

In late May 2003, Fisheries Officers from Alexandra and Wangaratta, with assistance from local Police, apprehended 4 anglers fishing for trout in the permanently closed section of the Goulburn River, immediately below the Eildon pondage. Three of the anglers were issued $100 on-the-spot fines. The fourth angler received a warning.

Anglers are reminded that you may not use or possess fishing equipment in the waters or within 20m of the banks of the Goulburn River from the walkway over the Eildon pondage Weir release gates to the fishing boundary posts 200m downstream from that point. This offence carries a maximum penalty of $2,000 and confiscation of fishing equipment. Refer to p56 of the 2002/03 Victorian Recreational Fishing Guide for more information about this and other 'closed' or 'restricted' waters.


For more information contact the Customer Service Centre - ph 136 186.

This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.

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