Ever wondered what fish were actually in your local rivers? There are always those reliable reports from local fisherpeople about ‘the one that got away’, as well as the relaying of information about those caught in years gone by that were ‘this big’. Although these stories are always entertaining, there is another way to find out – and apart from the logistics of getting a boat into some of our smaller waterways – is a lot less time consuming and slightly more reliable than chucking a line in (for those of us who don’t get to go fishing).
It is called electrofishing, and involves putting an electric current through the water (via boat or backpack) which temporarily stuns all the fish in its path, causing them to float to the surface. University of Canberra recently undertook some electrofishing for our Rivers of Carbon-Yass River Linkages Stage Two project, to follow up on some fish surveys undertaken by the Department of Primary Indiustry and Fisheries a couple of years ago along the Yass River.
At each site of the four sites, 12 x 90 second shots were employed, with the exception of one site, where restricted access allowed for only 8 x 90 second shots to be completed. All fish captured were identified to species, measured (nearest mm) and weighed (nearest g). In comparing with previous and future fish surveys of these sites, it must be noted that this survey was undertaken in winter with cooler water temperatures (9 – 11 ⁰C), which can reduce capture rates of fish, especially small-bodied species. The sites differed in their instream and riparian habitat (see Table 1).
Table 1. Site description notes taken whilst sampling.
|Hume Bridge||Largely devoid of riparian vegetation, especially on southern bank. Some cover from overhanging vegetation and emergent and submergent macrophytes.|
|Zamerhof||Healthy native riparian zone with trees, shrubs and grasses. Instream cover abundant, in the form of structural woody habitat, rock outcrops and overhanging vegetation.|
|Goldenholm||Somewhat healthy riparian zone, cleared of willows. Instream cover relatively sparse, mainly undercut banks and some structural woody habitat.|
|Grubb||Riparian vegetation thick and overgrown, some native and some willows. Instream cover abundant, comprising structural woody habitat and overhanging vegetation.|
Site photos from Hume Bridge with its largely cleared riparian zone and Zamerhof with restored native riparian zone. The three sites Zamerhof, Goldenhom and Grubb are all Rivers of Carbon Yass River Linkages landholders and we thank them for allowing us to access their river for the electrofishing expedition.
A total of 61 fish were captured, comprising two native species (Murray cod and Golden perch) and two invasive species (common carp and redfin perch) (Table 2). Common carp were the most abundant species at every site. Murray cod were present at two sites (Hume Bridge and Zamerhof), and Golden perch were only present at one site (Hume Bridge) (Table 2). The only juvenile fish captured was a redfin from Hume Bridge (110 mm fork length). No small bodied species were captured or observed at any site during the survey.
Table 2. Number of individuals of each species (including length range) captured boat electrofishing at each site on the Yass River in August 2019.
|Site||Common carp||Murray cod||Golden perch||Redfin perch||Total|
|Hume Br||15 (401 – 630 mm FL)||2 (468 – 600 mm TL)||3 (427 – 473 mm TL)||1 (112 mm FL)||21|
|Zamenhof||19 (453 – 536 mm FL)||1 (745 mm TL)||0||0||20|
|Goldenholm||9 (385 – 542 mm FL)||0||0||0||9|
|Grubb||11 (404 – 508 mm FL)||0||0||0||11|
FL = Fork length, TL = Total length
So we are pleased to discover that there are still a number of native fish surviving in the Yass River, and this is in spite of all the Carp, Redfin and other less desirable species. Our surveys were undertaken in winter so the water temperatures were cold and breeding for most fish species won’t happen for a few more months. We would like to go back early next year to see if we can find some of the small bodied native fish we care about, like the Southern pygmy perch, in the Yass River.
Projects such as Yass Rivers of Carbon, the Yass River Rehabilitation project and other Landcare and government initiatives are helping our native fish survive by removing willows, fencing the river from stock and replanting. We would like to thank Yass Area Network of Landcare, University of Canberra, DPI Fisheries and all those wonderful landholders who care so much for their creeks and rivers.
Yass River Linkages
Rivers of Carbon: Yass River Linkages is a project that supports and extend the efforts of the Yass Area Network of Landcare Groups and others, who are committed to bringing the Yass River ‘back to life’.