10 March, 2012

Invasion forces

Not all of the flora and fauna to be found along the Barwon River is native in its origin. Of course, there are plenty of eucalypts and wattles, kookaburras and cockatoos, but there are also many foreigners.
Common Starling

Some of the most obvious introduced species are birds. Through the urban areas of Geelong, the Common Myna is regularly seen as are Common Blackbirds, Rock Doves (aka feral pigeons), Spotted Doves, Common Starlings and House Sparrows. All were introduced to Australia in the mid to late 19th century from Asia or Europe and have made themselves very much at home.
Blackbirds, starlings, sparrows and mynas have all become pests, affecting crops and urban gardens across the eastern part of the country whilst nesting pigeons can create unsightly messes on and around buildings.
Rock Dove aka Feral Pigeon
Another species which has been introduced to Australia and to the environment of the Barwon is of course the rabbit. This was introduced to the district in 1859 by Thomas Austin of Barwon Park near Winchelsea as I mentioned in a previous post.
Rabbit on the banks of the Barwon
It took barely a decade before the rabbit population exploded, causing soil erosion and untold damage to native plants. It has been suggested that the rabbit is the largest contributing factor to the loss of native wildlife in the country. Over the last century and a half, various measures have been taken to control the rabbit population including trapping, hunting, destruction of rabbit warrens, the erection of a rabbit-proof fence and in the 20th century, the introuction of the Myxoma virus in 1950 and then in 1995 the calicivirus.
Carp at Breakwater
Unfortunately, none of these measures has been successful in eradicating the rabbit population and in recent years, the return of sufficient rainfall to end the drought and increase food supplies has of course resulted in a huge upsurge in the rabbit population across Victoria. This is also true along the banks of the Barwon and its tributaries. Measures are currently being taken to cull them with baits laid along the river, however there still seem to be plenty of them to be found.
Other pests which are not so easy to see can be found in waterways throughout the country. Carp are common in the Barwon and are often caught by fishermen as are redfin. Both are introduced species which compete with native fish for resources. Carp are omnivorous, eating plants, insects, zooplankton and other small organisms. Significant reduction in the levels of zooplankton can leave rivers susceptible to algal blooms. Redfin eat other smaller fish and the young of larger fish, reducing the numbers of native fish and putting strain on their food supplies.
Mosquitofish in the Moorabool River at Fyansford
Another tiny immigrant which has found its way into the Barwon river system is the mosquitofish. These fast moving little fish form schools which swim close to the water's surface making them relatively easy to spot. They were introduced in the north of Australia in 1925 in a bid to control mosquito numbers, however as with many such introductions, the mosquitofish has done more harm than good and its effect on the mosquito population has been negligible. It is now believed that some native species of fish do a better job than the mosquitofish for which mosquito larvae form only a portion of their diet. In addition to the larvae they also consume algae-eating zooplankton with the result mentioned above and a variety of insects and beetles, reducing food supplies for other native species.
Mosquitofish are aggressive, attacking other fish causing injury and infection, they breed prolifically, are resistant to many of the toxins and chemical pollutants found in waterways and can survive in a wide range of temperatures and salinity levels enabling them to out-compete almost any other species of fish.


  1. Interesting report on introduced species.
    Somewhat gloomy, unfortunately, for good reason.
    I suspect the Carp will rate with the Rabbits in terms of damage to the river environment.

  2. Thanks Denis. What I noticed is that the birds don't seem to get such a bad wrap as other species. Most of the complaints there are about damage to crops and gardens which are also introduced. I didn't get around to introduced plant species either...maybe the next post...