Boise Valley Fly Fishers
Since 1971


Boise River Side Channel Fry Survey

26 Nov 2023 9:28 AM | Troy Pearse (Administrator)

Last week I got the opportunity to help Tim D’Amico, Idaho Fish and Game fisheries biologist, with a trout fry (electro-fishing) survey on the Boise River side channel where BVFF has been working on trout habitat improvements (see this Conservation Blog article for details). We surveyed the same 3 spots as last year--one at the top, one mid-channel and one in the lower section. The total fry numbers were down compared to last year, but that was mainly because the tree across the channel at the lower site where we had found so many trout fry last year had pushed downstream and we only found a couple of trout in that zone. The fisheries biologist said that was one of the limitations of their fry survey--that changes to the river can impact the productivity of a sample site. (See this Conservation Blog article for more information about last year's fry survey.)

One of the habitat improvements we did on the side channel last February was to place a tree root-wad in the upper section, with the assistance of the flood district’s excavator. This year’s high runoff flows scoured out a good hole there and we found both fry and 1–2-year-old brown and rainbow trout holding around the root-wad. Seeing the age 1-2 trout is extremely exciting because it is a good indicator that our side channel habitat improvements are helping trout over-winter survival, which IDFG tells us is the bottleneck for improving recruitment from fry into adulthood.

I passed along photos and kudos to the flood district and will be working with the new flood district manager, Mark Zirschky, to identify other downed trees that can be possibly be repurposed/placed in other locations to improve trout habitat during their winter operations. This opportunity to improve woody cover in the Boise River is extremely important and I am grateful for their forward thinking and willingness to help protect and improve trout habitat in the Boise River. (See this Conservation Blog article for more information on this awesome project!)

I had been concerned that the high flows from the early release of water in April would be a problem because it occurred so close to brown trout fry-out (when the fry leave their redd/nest), but we found lots of brown trout fry indicating that the side channel and woody cover was a good place of refuge from the high flows. So far, I haven't seen any brown trout redds in our side channel this Fall, but I have seen some in the main river. During the survey we found one large (20") brown trout at the end of the side channel, who appears to be staged to spawn. Last year most of the spawning in the side channel happened in December, so I am hopeful we will see some redds soon.

BVFF will start floating the Boise river this week to document brown trout spawning and update the redd-zone map for the flood district so they can avoid the redds during their winter maintenance. The high spring flows recruited new gravel from the river-banks and it will be very interesting to see where we find brown trout spawning this year.

In December I will be participating in a trout fry survey at the Diane Moore Nature Center side channel (the same place we did our snorkel survey this summer). Flows are down significantly in that side channel, but there are some deep pools and lots of woody cover. The total number of trout fry we saw in that side channel last summer was amazing, and there is lots of good woody cover for them, so I expect we will see an increase in the adult population of trout there over the next few years. For more information about this successful side channel restoration, see this Conservation Blog article.

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