It’s been a busy few months for researchers surveying the 12 priority rivers, with work for this season completed just last week. To recap, the streams surveyed as this part of the program (Project 2) are the Mitta, Kiewa, Ovens, King, Delatite, Jamieson, Howqua, Upper Yarra, Toorongo, Dargo and Aire rivers; and Nariel Creek.
The Ovens River – one of the 12 priority rivers being investigated.
Among other things, Project 2 will measure the health of wild trout populations in these rivers, including things like the abundance of young trout – indicating the extent of natural breeding success. Surveys will continue over 3 years to account for annual variations. The contribution of stocked trout to the upper Goulburn and Howqua rivers (these fish are distinctly marked) is also being measured as part of Project 8.
Wild trout electro-fished from the upper Ovens about to be measured, recorded and released – researchers have observed a big increase in numbers of wild Ovens trout since a survey soon after the bushfires in January 2013. (pic J Lieschke)
The data gathered this season is yet to be fully collated and checked, but chatting to the researchers, a couple of interesting features are already apparent. One is the number of large trout turning up in some rivers – quite a few over 1 kg and some approaching 2 kg. Regular fishers of the streams listed above will know that trout of this size aren’t caught very often in a typical a year. Another feature appears to be the abundance of young rainbows in certain streams, indicating distinctly more successful natural recruitment of this species recently – at least for some waters.
Over the last few months, researchers have recorded a number of very large wild trout in several of the priority rivers. (pic J Lieschke)
Meanwhile, we’re not far off the first download of data from the electronic listening posts on the Delatite River, which will happen in the next month or so. Regular readers of this blog may recall that last year, researchers fitted 100 wild Delatite trout with acoustic tags. These tags ‘tell’ the listening post every time a particular trout swims past. The listening posts are placed all the way up and down the Delatite and as they also take regular water temperature readings, this part of the program (Project 1) will tell us about the natural movement of wild trout in response to water temperature changes. Do these trout simply ‘ride out’ dangerously high water temperatures? Do they migrate upstream to cooler water to avoid these high temperatures? And if so, do they head back downstream again once temperatures moderate? Hopefully we’ll start to get a clearer picture soon.
