brook trout and terrestrials in intermittent appalachian streams

[k-bob]

http://onlinelibrary.wiley.com/doi/10.1111/fwb.12221/pdf

I like the focus on intermittent streams. the aquatic bugs may be burrowers or consumed by baitfish, reinforcing the importance of vegetation along and above streams to provide terrestrials for brook trout when they cant move between pools.

 

[k-bob]

whoops I had been looking at this article on a system that linked thru to the entire report. I'll take the liberty of copying a snip from the conclusion describing the diet of brookies isolated in pools by low flow conditions of intermittent streams:

"In our study, benthic resources were already the most
abundant source of invertebrates, but despite this, aquatic
invertebrates did not comprise an equally large part
of brook trout diets. This is surprising because if aquatic
invertebrates were accessible, brook trout in intermittent
streams should be more likely to switch to this resource
because fish were confined to isolated pools and could
not migrate to areas with greater terrestrial inputs as
seen with native charr in perennial streams (Kawaguchi
et al., 2003). We suspect that the majority of benthic
invertebrates in our study area were largely unavailable
as prey because of their smaller size and hiding potential." ...

"Brook trout also may have restricted foraging on
aquatic invertebrates because of competition with sculpin,
which feed solely from the benthos. Brook trout
and sculpin may not compete for food resources in
perennial streams (Cheever & Simon, 2009), but this
could change when flows are reduced and brook trout
can no longer feed on the drift."

reinforces the importance of terrestrials to brookies even when isolated in pools by low flows..

 

[k-bob]

fun image from study. they covered the stream to cut off the terrestrials. don't try "terrestrial exclusion nets" at home

 

[geebee]

Interesting - you never think of sculpins as competitors to trout, more as prey for them.

Which suggests to me that if you see or catch a sculpin in a small brookie stream you're best of knocking it on the head.

 

[troutbert]

The gist of the article seems to be that brook trout eat a lot of terrestrials. Many brook trout anglers are well aware of that and have a lot of terrestrial imitations in their fly boxes.

But what is the conservation take away from this? What does it mean in terms of what should be done regarding stream or land management?

 

[k-bob]

yeah, we all knew that brookies love terrestrials. this study artifishially (!) creates very low conditions of terrestrial availability, and studies the diet of brookies. the brook trout did not switch over to aquatic bugs as much as might have been expected, in part because theaquatic bugs were hidden diggers and/or taken by sculpins.

mgt takeway: terrestrials are even more important than previously believed in small-stream brookie diets, so maintenance of vegetation along and above streams is even more important than previously believed.

 

[KenU]

Agreed. I have done some studies of acid precipitation impacted streams that have almost no aquatic insect life. However, there are still a fair number of brookies and they occasionally reach 10 inches. The only thing I can imagine is that they are subsisting mainly on terrestrials.

 

[geebee]

I think what this study reiterates is the importance of riparian buffers of two feet of more - a lot of bird and bug societies are lobbying frames right now to leave 3ft at each field end for bugs, butterflies and birds to have some where to prosper.

Streams are the same.

 

[troutbert]

I have not heard about the bird and bug societies 2-3 feet field buffers.

But in the stream conservation field, riparian buffers are typically much wider than that. They need to be, to have any significant benefit.

 

[pcray1231]

But in the stream conservation field, riparian buffers are typically much wider than that. They need to be, to have any significant benefit.

Agreed, but you're looking at benefits in terms of shade/water temp, runoff control, etc.

3 ft may not be optimal, but might actually be significant in terms of attracting terrestrial food items.

 

[geebee]

troutbert wrote:
I have not heard about the bird and bug societies 2-3 feet field buffers.

But in the stream conservation field, riparian buffers are typically much wider than that. They need to be, to have any significant benefit.

In a stream you're looking to provide shade and filter acid rain and storm run-off, on farm land you're looking to maintain pollinaters and habitat lost due to the pulling down of hedgerows for the giant factory farms for corn, soy and rapeseed etc.

Obviously bigger buffers are much better but for grain and cereal farmers space is money and 2-3 feet is enough apparently for wild flowers, bees, birds and voles etc.

 

[Chaz]

In places like the Upper Schuylkill River where there are no aquatic bugs in many streams the brookies subsist on terrestrials and other fish. Many of those streams don't have sculpins, but do have other fish, mostly brookie you, that the larger fish eat.
In studies by Stroud Water Research they found that brookies in the Upper Schuylkill had stomachs full of aphids. In a PFBC study they found the brookies full of those 1 inch long millepedes.