Journal of the Royal Society of Western Australia, 90(3), September 2007 
Figure 1. The location (and number) of Goldfish (Carassius auratus) captured in the Vasse River during March 2003 and December 
2004. N.B. Catch locations remained consistent in subsequent years. 
listed as a Ramsar Wetland of International Importance 
(Jaensch & Lane 1993, Pen 1997). In appreciation of the 
importance of natural stream morphology and riparian 
vegetation in creating healthy stream ecosystems, the 
Lower Vasse River Cleanup Program, coordinated by the 
Geographe Catchment Council, has undertaken 
reshaping and revegetation of the bed and banks of the 
Lower Vasse River while and conducting Phoslock'" trials 
to reduce dissolved phosphorus and thereby attempt to 
reduced blue-green algal (cyanobacteria) blooms in the 
river (Goss & Greenop 2003). During these works, the 
reported sightings and capture of feral fish such as 
Goldfish in the Vasse River has increased considerably in 
recent years. 
Capture techniques 
The distribution of feral Goldfish within the Vasse 
River was determined in December 2003 and March 
2004, and goldfish removal events (for population 
control [see below]) occurred during March 2005, May 
2006 and September 2006. Although sites were 
sampled throughout the catchment. Goldfish were 
restricted to the lower Vasse River (see Figure 1). As 
the lower Vasse River is a large body of water relative 
to upstream reaches due to slot board insertion and 
the Vasse River Diversion Drain, a number of methods 
were employed to capture as many Goldfish as 
possible. This initially involved the use of gill nets, 
seine nets and a back-pack electrofisher (a device that 
momentarily stuns fish). However, the subsequent 
Goldfish captures were achieved utilising a 240 volt, 
generator-powered electrofisher deployed from a boat. 
The entire stretch of the river from - 500 m upstream 
of the Bussell Highway Bridge to immediately 
downstream of the Old Butter Factory slot-boards was 
electrofished at least twice on each sampling occasion 
with the exception of December 2003 (see Figure 1). 
Key Goldfish habitats were revisited on each sampling 
occasion (see results). The latitude and longitude of 
each Goldfish capture was recorded using a GPS and a 
map of the distribution of Goldfish captures was 
produced using the Mapinfo™ program. 
Biological techniques 
Each Goldfish captured was placed immediately in an 
ice slurry and, upon return to the laboratory, measured 
to the nearest 1 mm total length (TL) and weighed to the 
nearest 1 mg. A length-weight relationship was produced 
via testing a number of models and the one that provided 
the greatest fp value adopted as the best fit of the data. 
The stomach contents of a sub-sample of 20 Goldfish 
from a wide size range were removed and the contents 
classified into a number of prey categories. The frequency 
of occurrence and points method (Ball 1961, Hynes 1950) 
was used to food items in the stomachs of GoldfLsh and 
the relative contribution (by volume) of each prey 
category to their diet. 
For age determination, the otoliths of each Goldfish in 
152 
