At the conference, Fisheries ED Travis Dowling made the point that the Wild Trout Program isn’t just about research for the sake of research. As interesting as the findings to date may be, the idea is to actually use this information to make our trout fisheries better.
One of the things that kept coming up at Talk Wild Trout was the benefits of bankside trees to trout. For example, researcher Jason Lieschke commented that when he was viewing the temperature data from the various listening posts on the Delatite River (https://flystream.com/2015/01/19/acoustic-tracking-of-wild-delatite-trout-underway/) he was struck by the difference in water temperature between the shaded forested stretch (Receiver 1) and the first receiver in cleared farmland (Receiver 2). The former recorded a summer maximum of 23.1 C with a maximum daily variation of 7.2 C. However the latter, just 9.5 km downstream, peaked at 27.8 C with a daily range of 9.8 C.
The location of receiver 2 on the Delatite in farmland compared to 1 in the forest. Less than 10km downstream, but nearly 5 C warmer. (Image courtesy J. Lieschke)
How warm the water in a stream has to be before it really harms trout depends on a range of things including water quality, how long the high temperatures last, acclimatisation period, species (rainbows tend to be slightly more temperature tolerant than browns) and trout size. However one thing is for sure: once water temperatures climb into the high twenties for any length of time, trout survival is threatened. Yet research from the Wild Trout Program shows that on the lower reaches of many of the priority trout streams, summer water temperatures in this range are reasonably common. As per the first blog https://flystream.com/2015/11/24/talk-wild-trout-conference-21-november-pt-1-the-trout/ the reduced numbers of trout found downstream compared to upstream, is likely in large part to be summer temperature related. So, what can we do to mitigate that?
Creating shade in the form of bankside vegetation is clearly one practical way. Most small to medium-sized trout streams can be shaded for much of the day by a decent perimeter of trees on both banks, reducing both maximum water temperature and temperature fluctuation. And that’s aside from all the other benefits good riparian vegetation brings such as cover from predators, habitat for trout food, reduced erosion and silting, etc.
This stretch of stream might be comfortable to fish, but when summer arrives, the lack of bankside vegetation will leave it exposed to full sun. Potential erosion isn’t great either.
Talk Wild Trout keynote speaker, Trout Unlimited’s Dr Dan Dauwalter, pointed out that many of the temperature issues impacting Victorian trout streams are similar to those being faced in his home state of Idaho in the USA. And it seemed every second slide Dan showed was of TU volunteers planting trees along streams!
Meanwhile, Mark Turner from the Goulburn-Broken Catchment Management Authority (CMA) spoke at Talk Wild Trout about anglers getting more involved in streamside revegetation, particularly in the context of managing willow issues. Some other CMAs say they’re also keen to get trout anglers participating.
It’s 30C and midday in December on tree-lined Snowy Creek, yet there’s still plenty of shade. Water temp. is just 17C.
With Victorian trout fishing presently enjoying the support of several key agencies, it seems to me there are real opportunities to move ahead with well planned, strategic replanting of native trees along our trout stream frontages; especially the lower reaches outside forest areas. As well as the other benefits mentioned, this will get the shade up and water temperatures down. It isn’t a quick or easy fix, but it will create better fishing into the future on our trout streams.
