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Clarence freshwater fish go with the flow

Clarence River Fish Track continues to undertake world class research investigating the influence of river flows and barriers (e.g. waterfalls and weirs) on the seasonal movements of freshwater fish species. A mini-report detailing the latest findings of the Fishtrack project has just been completed by Dr Gavin Butler of DPI Water.

Clarence Fish Track is a partnership initiative of NSW Department of Primary Industries, North Coast Local Land Services, Clarence Valley Council, Coffs Harbour City Council and Essential Energy with support from the National Landcare Programme and the NSW Recreational Fishing Trust.

Nigel Blake, Senior Land Services Officer said, “It is great to be have a world class fish monitoring programme right here in the Clarence and the knowledge generated by Clarence Fish Track is of interest to many people from all areas of the community.”

The project is assisting river managers, recreational fishers and the international scientific community to better understand and manage the region’s precious freshwater fish communities.

Over the 2015/16 season more than 30,000 individual fish were caught (and released) from 27 sites in the Clarence System.  Twenty eight different native fish species and two introduced species, goldfish and eastern mosquitofish, were found.

Encouragingly, the endangered eastern freshwater cod (Maccullochella ikei) was present at a number of sites in the Orara, Clarence, Mann and Nymboida rivers. Other large species caught include, catfish, bass, herring, eels, and freshwater mullet.

Using an internationally recognised method of analysing fish numbers, diversity and breeding at the 27 sites in the system an overall health score was determined. All sites in the Clarence System had good or excellent scores for indicators of both diversity and nativeness (lack of introduced species).

A low number of juveniles (recruitment) for many samples resulted in the overall health scores being reduced to moderate in the winter season.  However, juveniles were found at many sites in the system over the year, indicating that most species are successfully breeding in parts of the system and overall, fish numbers have not reduced over the ten years of Fish Track monitoring.

The study also reports on the movement of fish implanted with acoustic tags that monitors their movements upstream and downstream. The tags emit a beep that is detected by the receivers placed throughout the Clarence System in what is the largest detection array in the southern hemisphere.

Flow was typically low across all parts of the basin during 2015-16 and only two rises over two metres were recorded at the Lilydale Gauging Station. This is most likely the reason that movement by tagged fish were overall fewer in number and shorter in distance than last season with most tagged fish staying near where they were released. This is in contrast to seasons when river rises coincide with breeding seasons.

These seasons saw migrations by many Australian Bass and Freshwater mullet of over 300 km, while other tagged species displayed greater movement upstream and downstream.

Nigel concluded, “The Clarence Fishtrack project has confirmed that the Clarence Catchment has a unique and resilient fish population.

“We have proven that barriers and flow have a major influence on the natural movements and migrations of our native fish.

“We need to carefully consider the influence of any projects on the Clarence that may have the potential to modify natural flood patterns, block natural migration pathways, and will severely and irreversibly affect many of our native fish such as Australian bass and the endangered eastern freshwater cod,” Nigel concluded.

Media contact:           Nigel Blake, Senior Land Services Officer, Phone 0427 666 462

Photo caption:           Captured eastern freshwater cod - tagged and measured prior to release.