This project seeks to better understand how fish respond to flows and help better manage the Edward-Wakool river system and environmental flows. The project has two components:
- electrofishing, which tells us about the types and numbers of fish present; and
- acoustic tagging, which is used to track the movement of fish through the system.
This work is being undertaken by scientists from the Narrandera Fisheries Centre (NSW Department of Primary Industries) and the Murray Catchment Management Authority (CMA), funded by Primary industries NSW, the Murray CMA and under the Commonwealth environmental water program.
Some of the fish tracking results are shown in the video below. Up to 140 Murray cod, golden perch, silver perch and carp were implanted with acoustic tags and their movement was monitored though the Wakool River, Yallakool Creek and Edward River. The video shows that fish congregate in refuge pools when flows are low and steady. When higher flows come through the system, fish move quickly up and down the river, before returning to refuge pools when flows drop away.
A number of studies have shown that movement of Murray cod is important to breeding. It is thought that the fish are moving upstream immediately before spawning occurs to compensate for the downstream drift experienced by newly hatched fish larvae. Other reasons for moving could be to find food, to avoid unfavourable conditions (such as blackwater) and colonisation of new habitats.
The video shows the period from August 2010 to March 2011, during which time both rainfall and Commonwealth environmental water contributed to river flows. These results are being used to help plan for environmental watering in the Edward-Wakool system in the future.
Detailed description of fish tracking video
The video shows fish movement in response to river flows in the Wakool system in 2010. The first screen is a map of the part of the Edward-Wakool system showing where the fish were tagged (the junction of the Wakool River and Yallakool Creek) and each of the fish tracking receivers (the green dots).
The tracking receivers recorded over 3 Million data points in the first 6 months. Scientists analysed the data and were able to display it as the movements of Murray cod. The video shows:
- The movement of eight Murray cod. Each individual fish is a different colour green line.
- The flow in megalitres per day (the hydrograph) through the Wakool River (the blue line) and Yallakool Creek (the red line) are shown in the window on the left hand side.
- The Wakool River (the bottom watercourse on the map) and the Yallakool Creek (the top watercourse on the map).
- The date in real time, where 2010-09 means September 2010.
The footage begins when the Wakool River and the Yallakool Creek are a series of refuge pools and all the tagged fish are in the large refuge pool at the junction of the Wakool River and Yallakool Creek. At the end of August (19 seconds on the video timer) as small flows begin to reach the junction of the two water courses, some of the fish become active within the refuge pool.
In mid September (25 seconds) flows in both the Wakool River and Yallakool Creek begin to increase. The refuge pools link together with the high flows in September 2010 and the fish begin moving and exploring the system. The longer and faster the green line, the faster the fish is moving.
Towards the beginning of October (35 seconds) the flow peak has passed and many of the fish return to their original location at the junction of the two water courses or taken up new positions in other refuge holes.
In mid November (55 seconds) flows in the Yallakool Creek drop quickly to very low levels. This was due to the completion of a 'block-bank' at the top of the creek to enable the construction of a new water management regulator and fishway to allow fish passage between the Yallakool Creek and the Edward River. There is very little fish movement in the Yallakool Creek when the flows were low, however the fish continued to move in the Wakool River where the flows were much higher.
Towards the end of December (1 minute 12 seconds) a second high flow event occurred. The flows were so large that the block-bank at the top of the Yallakool Creek was destroyed and high flows passed through the system again. The film shows that the fish are very active again when the high flows move through the Yallakool Creek.