Ideal Brook Trout Habitat

[jeffroey]

I set a goal this year to get better at reading rocks . . . learning new ways and finding new info sources that allow me to quickly differentiate whether a stream prospect is running over bedrock formation(s) with desirable buffering characteristics. I'm going to put that in a holding pattern for another thread.

I mention it because that goal is forcing me to keep sight on the fact that geology really doesn't matter much if you don't have good habitat. AND THAT is sending me down the habitat rabbit hole. I found an interesting (to me) source document circa 1982 that proposes a "Habitat Suitability Index" for brook trout to aid in "impact assessment and habitat management activities".

Here's a link to the source: https://www.govinfo.gov/content/pkg/GOVPUB-I49-PURL-LPS101790/pdf/GOVPUB-I49-PURL-LPS101790.pdf​

There's good discussion on "Specific Habitat Requirements" (p.11-13 of 53) that I think is very informative and worth the read. The paper eventually distills down to a simplified HSI model option for brook trout (p. 35 of 53) that assesses eight (8) fundamental habitat measures:

1. Clear, cold water with an average maximum summer temperature of <22° C (71.6 °F)
2. Approximately a 1:1 pool-riffle ratio
3. Well vegetated, stable stream banks
4. 25% of stream area providing cover
5. Relatively stable water flow regime, < 50% annual fluctuation from average annual daily flow
6. Relatively stable summer temperature regime, averaging about 13°C ± 4°C (55.4°F ± 7°F)
7. A relatively silt-free rocky substrate in riffle-run areas
8. Relatively good water quality (e.g., DO and pH).

The HSI = the number of attributes present divided by 8 with 0 being worst and 1 being ideal.

I'm over-simplifying the conclusion of the paper but you have the context for my ask. There are threads on the forum discussing HSIs primarily for Smallmouth but I didn't see very many refs (maybe 1) to HSIs for brook trout.

Question is . . . aside from the (8) habitat characteristics I copied in above, what do you consider when assessing if a brook trout habitat is good or bad?

 

[5footfenwick]

I have two I’ll throw in there from personal experience. Not sure if they technically count though.

9. I personally really like at least one big deep (relatively to the rest of the habitat) hole , somewhere in the stream. Obviously this will draw browns if present. But if it isn’t loaded with browns, I feel like this gives the brook trout somewhere to go in winter and in really hot dry summers. Most of my favorite brook trout streams have at least one of these hidden swimming holes. Although it could be only 4 feet deep in a stream that averages 4 inches deep. But I think it really makes a difference.

10. This is a little different take, but one that I use all the time. I like to really look at the habitat of the mainstem. ie downstream from the mouth of the brook trout stream for a mile or two. If this habitat is good, I think it gives the brook trout a place to migrate/ travel to when water temperatures are colder. Some of these fish migrate into and out of the tiny BrookTrout trickles. Having access to bigger water/ nice holes/increased food seems to really boost the size of the Brook trout I catch in the tiny brook trout streams.

Not sure if the habitat directly downstream from mouth of a brook trout trib really counts as habitat for the brookie stream. But in my opinion it should. It makes a huge difference in size of the fish I catch. Instead of that tiny trickle only having 6” fish. I occasionally have found some loaded with 9-11” fish. I know they can’t make a living in the tiny stream year round. There just isn’t enough food. And they can’t survive in the mainstem year round because it gets too warm. But at times they are there in a tiny trickle. Stacked up. And other times they are not there. I can only assume they drop down stream at some point. Feed up in the cold mainstem and then seek thermal refuge in the tiny trickle again when they need to. At least that’s my theory.

 

[5footfenwick]

Here is picture of a tiny trickle with more big trout than food. Before anyone says these fish are spawning, they are not. Not yet anyway. I know this for a fact. They were all males. Smallest one was 9-3/4” and largest was 11-1/4” I got lucky and actually somehow caught and landed all five. This picture was taken after I caught and released all of them. And walked up on the tiny hole for a look. First hole up from the mouth of this trib to a big warm river. This hole had no hiding places. No undercut rocks. Nothing. I think they were on their way upstream. And they certainly don’t live in this tiny trickle year round. Just a very weird thing I had to snap a photo of. Probably should have bought a lottery ticket that day.

 

[Mike]

Item 1 above doesn’t appear to take into account mortality or inability to reproduce associated with exposure time to lesser yet still stressful temps.

Item 6 above in round numbers F should be 55+ or - 7deg F

 

[jeffroey]

Item 6 above in round numbers F should be 55+ or - 7deg F

Thx Mike. I fixed my typo.

 

[troutbert]

Small forested streams that are on the PFBC's wild trout reproduction list are likely to have native brook trout. I recommend selecting streams that are on public land, so that access is assured.

Then just go fish them. Go when water and temperatures are in good shape. And fish many miles of stream. You will learn more that way than in any other way.

 

[jeffroey]

Small forested streams that are on the PFBC's wild trout reproduction list are likely to have native brook trout. I recommend selecting streams that are on public land, so that access is assured.

Then just go fish them. Go when water and temperatures are in good shape. And fish many miles of stream. You will learn more that way than in any other way.

That's fair and it's pretty much exactly what I do. I'm not discouraged by a good looking stream that I don't have first hand info about and I'm always willing to roll the dice. Part of the fun for me.

That said, I'm betting many of you are like me and work from a checklist of sorts (actual or mental) when seeking out or assessing a stream that could be hours away by car and I'm certain many of you are better at this than I am. Just looking to share tips and mine out the habitat things that are important to you I may not be thinking about. Thx.

 

[k-bob]

I consider new brookie streams to fish from maps. some of that stuff you cant read from a map before you fish, such as flow stability = point # 5.

aren't points 1, 4, & 6 basically suitable water temp? DO in point 8 is associated w same. elevation plus forest cover are water-temp signs you can read from maps. I seldom have issues with that versus expected.

on point 2, pool v riffle, see below, p 41, on gradient (easy to read from maps). higher gradient => more holes. also recall that streams dig holes when they turn, so serpentine > straight for holes when other things are equal (such as gradient).

https://etda.libraries.psu.edu/files/final_submissions/1310

The issue referenced OP that I cant tell from maps is whether a stream will be messed up, sometimes severely, with sand filling up its holes ... I see this present and absent in nearby streams in the same bedrock formation. sometimes explained by road runoff etc but sometimes not. so still plenty of surprises once on a tiny stream out there.

imho the streams with tendencies to high brookie densities and relatively bigger fish are known. I am fine with a hike to a forest w great scenery I have never seen w a few brookies. maps are good for that.

 

[BradFromPotter]

Question is . . . aside from the (8) habitat characteristics I copied in above, what do you consider when assessing if a brook trout habitat is good or bad?

The only thing would be is if I catch brook trout assessing the stream. Why waste the time looking at the 8 items? Dude just fish said waters & you will find out.

 

[wildtrout2]

Here is picture of a tiny trickle with more big trout than food. Before anyone says these fish are spawning, they are not. Not yet anyway. I know this for a fact. They were all males. Smallest one was 9-3/4” and largest was 11-1/4” I got lucky and actually somehow caught and landed all five. This picture was taken after I caught and released all of them. And walked up on the tiny hole for a look. First hole up from the mouth of this trib to a big warm river. This hole had no hiding places. No undercut rocks. Nothing. I think they were on their way upstream. And they certainly don’t live in this tiny trickle year round. Just a very weird thing I had to snap a photo of. Probably should have bought a lottery ticket that day. View attachment 1641234600

Don't know how you managed to catch all five without them spooking after the first one or two, but never the less, that's an amazing experience you had! A rare sight for sure.

 

[jeffroey]

@k-bob Good to hear from you Bob and thx for your feedback.

Agree a lot the paper's criteria is hard to assess from lines on a map. Might be better acting as more of a gauge to explaining why there is or isn't fish in a particular stream once you're on it.

I know a lot of us rely on arcgis mapping resources when assessing, particularly the leaf-off layers often uncover a little info that's otherwise hidden . . .

Maybe whether that large pool @5footfenwick is looking for might or might not exist or whether the presence of falls that could be telltales for more turbulent water - good for both DO levels and even turbulent flow cover (admittedly that one would be hard to decypher from a map).

Putting the paper's discussion aside, the probability of DO and turbulence are two of my gauges . . . If the info supports. Others like if it's buggy or not, makeup of the stream bed as it pertains to providing cover, etc are more streamside measures.

Here's a direct link to the arcgis leaf-off layer:

https://www.arcgis.com/home/item.html?id=0cf4e8f921404bad84dc55f7fa93a46f

Using an Oblique view in the tool when available also works to clarify the stream condition

 

[5footfenwick]

Don't know how you managed to catch all five without them spooking after the first one or two, but never the less, that's an amazing experience you had! A rare sight for sure.

I don’t know why they didn’t spook either honestly. Not something that really usually ever happens with natives. My best guess is that they were really hungry. And were gonna get a meal no matter what I did. Perhaps due to lack of food?

The other strange thing is they didn’t really spook even when I walked up on the tiny hole. I had time to dig out my phone and snap a few pictures all while basically standing right over top of them. Like I mentioned, there was no cover, no undercut rocks to hide under, no where to hide. Overall it was a very unique and strange experience. One I don’t think I’ll ever forget. I just thought I’d share because it was really neat and seemed to be an example of what I suggested in #10. That the habitat in the mainstem added much larger fish to the tiny trickle with poor habitat.

 

[wildtrout2]

I don’t know why they didn’t spook either honestly. Not something that really usually ever happens with natives. My best guess is that they were really hungry. And were gonna get a meal no matter what I did. Perhaps due to lack of food?

That was the only explanation I could come up with as well. With natives, it's usually one or two and that spot shuts down quickly. The size of those fish was also interesting. It's a rare day when you can catch that many real good size natives on the same stream, let alone the same pool. It was your day!

 

[troutbert]

I set a goal this year to get better at reading rocks . . . learning new ways and finding new info sources that allow me to quickly differentiate whether a stream prospect is running over bedrock formation(s) with desirable buffering characteristics. I'm going to put that in a holding pattern for another thread.

I mention it because that goal is forcing me to keep sight on the fact that geology really doesn't matter much if you don't have good habitat. AND THAT is sending me down the habitat rabbit hole. I found an interesting (to me) source document circa 1982 that proposes a "Habitat Suitability Index" for brook trout to aid in "impact assessment and habitat management activities".

Here's a link to the source: https://www.govinfo.gov/content/pkg/GOVPUB-I49-PURL-LPS101790/pdf/GOVPUB-I49-PURL-LPS101790.pdf​

There's good discussion on "Specific Habitat Requirements" (p.11-13 of 53) that I think is very informative and worth the read. The paper eventually distills down to a simplified HSI model option for brook trout (p. 35 of 53) that assesses eight (8) fundamental habitat measures:

1. Clear, cold water with an average maximum summer temperature of <22° C (71.6 °F)
2. Approximately a 1:1 pool-riffle ratio
3. Well vegetated, stable stream banks
4. 25% of stream area providing cover
5. Relatively stable water flow regime, < 50% annual fluctuation from average annual daily flow
6. Relatively stable summer temperature regime, averaging about 13°C ± 4°C (55.4°F ± 7°F)
7. A relatively silt-free rocky substrate in riffle-run areas
8. Relatively good water quality (e.g., DO and pH).

The HSI = the number of attributes present divided by 8 with 0 being worst and 1 being ideal.

I'm over-simplifying the conclusion of the paper but you have the context for my ask. There are threads on the forum discussing HSIs primarily for Smallmouth but I didn't see very many refs (maybe 1) to HSIs for brook trout.

Question is . . . aside from the (8) habitat characteristics I copied in above, what do you consider when assessing if a brook trout habitat is good or bad?

The article does not mention beaver ponds at all, and they are a big part of brookie habitat. On some small streams, one beaver pond probably holds more brook trout than the rest of the stream combined. I once caught 14 brookies on 14 casts on a brookie pond. I'm sure I could have caught more than that, but I left to explore on downstream.

A max temp of 71.6 F would be nice, but one of the best brookie streams I've fished gets up to 80F in the summer. There are tribs that provide thermal refuge.

Stream banks are not naturally stable. Stream channels move. Erosion and deposition are normal. Much of overhead cover is caused by bank erosion, i.e. the undercutting of banks, often under the resistance of roots of trees and other plants. As the tree roots get undercut, the tree leans, then eventually falls into the stream, tearing out a chunk of bank, and creating large woody debris. All part of the process.

It's rare to find 1:1 riffle-pool habitat. The amount of pool habitat is typically far less than that. Sad, but true.

Stable water flow regime would be nice, but that's mainly a feature of limestone spring creeks, which are dominated by brown trout. Freestone streams, where most of the brook trout are found, are very flashy. Extreme high and low flows are typical.

Medium to high pH is good for invertebrate life, so good for food supply. Food benefits all trout, including brook trout. But where pH is medium to high, brown trout thrive and compete strongly with brook trout. Some of my best brook trout fishing has been in stream stretches that too infertile for brown trout to survive.

 

[jeffroey]

@troutbert - I hadn't thought about giving some consideration to the presence of beaver ponds. Good feedback and thx.

Relative to your other comments pertaining to stream banks and riffle-pool ratio, I don't disagree that they're not common but I think that the article I started the conversation around sort of implies that the presence of all of that stuff is near "ideal conditions" The absence of any or all of it would result in an HSI lower than 1.

​

 

[Mike]

Regarding item #8, the DO comment is almost superfluous. DO, when adjusted for water temp and elevation in trout streams is almost always saturated in daytime. When it’s not, it’s about 99% of the saturation value, but sometimes it dips to 97%. Warmwater streams are usually at saturation too in daytime, but occasionally you find a site that is 90% of saturation. If there are high densities of aquatic plants, then DO may sag more than that at night, but I never took nighttime samples to find out how much so on such trout streams. Obviously, permitted and other discharges may cause a sag as well within the recovery zone, but again, I never measured much of a sag in trout streams. I’d say a daylight one of concern would be quite unusual even in the early morning with completely overcast skies following a warm night. I don’t say this to be critical of the info presented by the op; I only do so to point out that DO values are rarely limiting habitat factors for trout in Pa in comparison to other physical habitat and physico/chemical factors.