Current PA Brook Trout Population as Percentage of Original?

[troutbert]

k-bob wrote:
we may be talking past each other. here's the question I have brought up:

me: "if we had data for all the PA streams pre euro & present, incl tiny steep mountain ones, almost none would have better brookies now?"

Correct. I've explained the physical habitat reasons why already. Far fewer pools = far fewer trout.

Supposing you took even a smaller slice then 5% of the top streams, and took only the top 1% of streams.

The populations of even that top 1% would be not just less, but FAR less, than in the past. For the physical habitat reasons already explained.

Regarding the map shown earlier. It is not mapping populations. It is mapping miles of streams that have brookies now, as compared to the past in subwatersheds.

So there are a couple of things to consider when thinking about the answer to the original question:

1) The maps shows areas where brookies are totally extirpated in entire subwatersheds.

2) The maps shows areas where different percentages of stream miles have lost their brookies.

3) What the maps do not show, but which we've been discussing, is the percentage drop in population in the streams that still have brookies.

 

[k-bob]

I agree that of course there is total biomass loss in all streams, big and small, that went from brookies to browns. 100% loss. And there must be large biomass losses also in many of the bigger streams that have brookies now.

But are there very small, very steep, cold streams with woody debris accumulated in the 100 years since they were logged, that have as many brookies now as they ever did? I think there could be, because the old hemlock forest might have blocked streamside brush more than the replacement mixed forest and thus reduced terrestrials. I also don't think that such very small and steep streams, 7+% grade, really have far fewer pools now from logging 100 years ago.

no way to know and interesting to consider.

 

[k-bob]

any map that shows brookies being "extirpated" where some brookies exist will mislead readers.

 

[troutbert]

There are some other factors that affect brookie populations in the streams where they still remain.

Competition with brown trout. In many forested freestone streams that still hold brook trout, long stretches of the lower parts of the creek are strongly dominated by brown trout. There are still brookies there, and they show up in the stream surveys, but their populations are greatly inhibited by the brown trout.

One example, among many, is the well known Cedar Run, tributary to Pine Creek. From the mouth far upstream up to around Leetonia, the brown trout population is far higher than the brown trout population. There are still many brown trout even well above Leetonia. The brookies only rule in the very upper end of the creek.

Acid rain (acid precipitation) has been mentioned briefly. But this had a very large impact on brookies. There are many miles of streams where the brookies are just gone, from acid rain. Some of that mileage would show up in the databases and therefore the mapping.

But many streams are surveyed in the lower and middle ends, and wild trout are found, and the stream is put on the reproduction list as "headwaters to mouth."

But in areas of the state with geologies with low buffering, very often there are brookies in the middle and lower ends, but the very upper ends are too impacted by acid rain, so support no trout at all, or fish of any kind.

And there is often a transition zone, where there are brookies at certain times, then they get pushed back downstream by heavy rain or melting snow dropping the pH.

Those lost miles of streams at the upper ends in many cases are not recorded so not shown on the mapping.

Also, in the lower and middle ends of the acid rain impacted stream miles where brookies are found year around, often the numbers of brookies are low. Because the food supply, i.e. the insects and other inverts are reduced by the acidification. You can simply turn of the rocks and see that there are not many bugs.

 

[troutbert]

k-bob wrote:
any map that shows brookies being "extirpated" where some brookies exist will mislead readers.

That would mislead readers, if that were the case. I think pcray made the same point. But I have not seen any examples given.

If anyone has examples, let us know.

 

[troutbert]

I think the answer to the original question is very likely to be less than 5%.

My best estimate is 3%.

 

[sarce]

TB,

There are at least a half dozen unt's to the west branch of the brandywine in chester county that still hold decent native brook trout populations. They are all south of route 30. On the map that area is solidly in the gray color.

 

[k-bob]

k-bob wrote: "any map that shows brookies being "extirpated" where some brookies exist will mislead readers."

TB: "That would mislead readers, if that were the case. I think pcray made the same point. But I have not seen any examples given. If anyone has examples, let us know."

... the ebtjv map appears on websites showing brookies being extirpated - meaning locally extinct - in parts of PA that do have brookies. just put "eastern brook trout map" in a google image search, for example:

http://www.nature.com/scitable/knowledge/library/brook-trout-restoration-83031062

 

[troutbert]

At that scale, showing the entire eastern US on a small map, it's hard to see and display all the details. But it looks they have they have some small specks amid the grey showing the small, relict populations where they still persist among areas where brook trout have largely been extirpated.

The numbers of brookies that still exist in places like the Brandywine Creek drainage is very small. Be realistic about their numbers, when answering the original question.

 

[troutbert]

Here are the estimates made so far.

Current PA Brook Trout Population as Percentage of Original (by biomass i.e. weight)

Foxgap: maybe less than 10%

K-bob: 30% by number of fish, biomass a little less

pcray: 5%

sarce: 1%

troutbert: 3%

Anyone else?

 

[k-bob]

nice bad news table 🙂. imho biomass ain't everything. by numbers of fish, and numbers of streams, you'd get much less gloomy numbers. pat for example
guessed that a majority of streams that had brookies then have brookies now -- which tells a different and more relevant species preservation story than biomass?

seems that Brook trout have been relegated to several thousand smaller PA streams without being truly endangered

 

[sarce]

Maybe there are some specks there, you are right it is hard to see. It might be an illusion though. I dont see any other blocks of color that are that small anywhere else on the map. You are also correct that the number of fish is not that great at all. But the number of streams is still significant, imo.

K-bob I agree with your last sentence above. It's not so much that the numbers today are that low as the numbers back then would have been mind-blowing.

 

[k-bob]

right but in a way the loss of big fish in big waters might be more of a fishing issue than a species preservation one.

 

[k-bob]

Intersting topic. Our bio-mass loss estimates are based on raw guesses about the level 500 years ago. Clearly there were a lot more hemlocks then. I give the cite below for a study that compares the aquatic-invertebrate richness of hemlock- and hardwood- forest draining headwater streams in the Del Wtr Gap. It is a long and complex paper, but it notes that aquatic bugs varied by forest type and "streams draining mixed hardwood forests may be more productive" (see abstract). Streams draining hardwood forests had 2.7 times greater density of aquatic invertebrates (p 268) than streams draining hemlock forests. Aquatic invertebrates consume leaf litter, and on p 269 the authors note that another study in Michigan found that "hemlock needles decayed slower and supported fewer macroinvertebrates" than the leaves of other tested riparian plant species. Conifer needles may generally be poor food sources... etc.

I certainly am not suggesting that PA's total brookie biomass is higher overall now, but if some of today's small, cold, steep streams that have brookies and few browns were switched from hemlock to hardwood canopy by logging... there could in some such streams be more bugs and more brookies now, because hemlock leaf litter might have been less productive for macroinvertebrates. If so, these would be exceptions of course, but maybe the old heavily hemlock-forest PA was not exactly the trout haven we imagine -- at least in tiny headwater streams.

Of course I am not suggesting that logging was good, only that its effects are complex and we have very little info on the distant past. Logging raised the water temp of many big PA streams above what brook trout can handle, for example. But we have data on over 4000 streams with wild trout - the nat repro list - and more than half them probably have brookies, plus the various unassessed waters programs say there are thousands of untested small PA streams, many of which could also have brookies.

"Influence of eastern hemlock (tsuga canadensis) forests on aquatic invertebrate assemblages in headwater streams," Snyder Young Lemaire Smith 2002, Canadian Jl Fishes and Aquatic Sciences.

 

[BrookieChaser]

BrookieChaser wrote:
[color=009900]I'd say we're definitely less than 10% of historic biomass (probably less than 5%) across the state[/color].

I'll split that and say 7%.

 

[k-bob]

Here is another study suggesting that a switch from hemlock to hardwood forest types, as many small PA streams experienced, might increase headwater stream richness. The study finds that hardwood-draining streams were more rich in invertebrates than hemlock-draining streams. This may happen because hardwood leaf litter is a better invertebrate food source than hemlock needles.

http://harvardforest.fas.harvard.edu/sites/harvardforest.fas.harvard.edu/files/publications/pdfs/Willacker_NEN_2009.pdf

A switch from the denser hemlock to more open hardwood canopy does allow more light to reach streams, but some small PA streams have enough groundwater influence to maintain char-friendly water temps even with more light hitting them (for ex., many tiny nat repro streams with brookies).

Of course I am not saying logging was good, only that its effects are complex and not the same for all streams.

Brook trout biomass now versus pre -euro? Probably depends on the stream. Who knows? Perhaps some small, steep, PA brookie streams with good groundwater inputs that were logged 100+ years ago have higher invertebrate and brookie biomass now than they did half a millennium ago, because they now drain hardwood vs hemlock forest...

thanks for bringing subject up; hadn't given some aspects of it much thought before!

 

[k-bob]

or consider the ANF, which has some streams with brookies, probably due to good groundwater inputs keeping stream temps down. the ANF area had great hemlock forests that were logged. after the logging..., "a new forest did quickly grow. It was a different forest than the previous one, because conditions were now different. Shade-tolerant, long-lived trees like hemlock and beech gave way to sun-loving, shorter-lived species like black cherry, which readily germinated on the bare sunny ground. Cherry, red maple, black birch, and sugar maple became common species in the understory." (park website)

and some of the new trees such as maples drop leaf litter that is better food for in-stream invertebrates than hemlock needles.. see charts here:

http://www3.nd.edu/~underc/east/publications/documents/Maloney_94AMN.pdf

more invertebrate biomass could lead to more trout biomass...

 

[pcray1231]

Troutbert,

Interesting theory on the LWD.

I'm not so sure it's true that old growth results in more LWD than modern successional forests, though. There's certainly more woody debris in your typical 80-130 year old mixed forest than there is in the pockets of virgin, mostly Hemlock, forests I've been in. I don't know if that has to do with forest dynamics, or the fact that hardwoods simply decompose much slower than pine.

My back of the napkin theory has been as follows: In old growth forests, trees fall on a relatively infrequent basis. In younger forests, trees grow much more closely together, and as they get older, the "winners" continue on while the losers fall out. Those losers can sometimes be pretty large trees. Likewise, if the whole tree doesn't fall, but just branches, pines tend to have smallish branches that decompose quickly. Oaks, maples, etc. have very large branches that stick around a long time, get washed into jams, etc.

Now, you could have an argument about original streams being better based on acid rain, or remnant siltation that occurred during the logging boom. I'm not sure how the differences in forest mix play out. As was said, the original forests had a much higher % of pines in general, which would lead to more acidic soil. But how that compares to modern acid rain, I don't know, further keeping in mind that not all acids act the same. i.e. it's not simple pH, but also the TYPE of acid I'd think. And a pine overstory and the sponge-like soil underneath would certainly keep streams colder and flows steadier, but I think that our "best" 5% of brookie streams have good temps and flows anyway.

The last factor there has really been the death nail of the larger northern tier freestoners, which now get too warm. With the original forest they'd have maintained much better flows in the summer time, and much cooler temperatures. And those were the waters that contained the lion's share of the brookie population and biomass, on that I'd think we're in agreement.

Another question would revolve around the effect of beavers, which were much more common "originally". They certainly make some holding water but also can cause problems.

It's an interesting question. But my guess will say that our best 5% streams are better than their "original" average state. Simply because these things change over time, and they did even before the white man. Those 5% are at their best right now. It doesn't mean the overall picture is even close, even if you limit it to "small streams". i.e. more streams are worse than better. But by taking the top 5% you're probably selecting the ones that are better.

 

[pcray1231]

P.S. by total population numbers I'll go with 5%. Again, the lion's share of the "original" population was in the larger waters which now get too warm for trout, or else hold mostly brown trout. It takes a heck of a lot of "Laurel Runs" to match 1 Pine Creek, or even 1 Spring Creek.

If you limit it to "small" streams, I'd go with 30%. The fringes of the brookie range were nearly completely wiped out. Development and pollution wiped out many streams, leaving isolated populations, and isolated populations then die out easily due to drought, etc.

If you limit it to "small" streams solely within the primary brookie range of PA, I'd go with 60%. A few were wiped out, a few were taken over by browns. The vast majority still contain brookies but most of those are degraded somewhat by one thing or another. Acid rain, development, more boom/bust flows due to hardwood forests not holding as much water as pine forests, etc.

But our current best 5% are probably as good or better than ever.

 

[troutbert]

pcray1231 wrote:

I'm not so sure it's true that old growth results in more LWD than modern successional forests, though. There's certainly more woody debris in your typical 80-130 year old mixed forest than there is in the pockets of virgin, mostly Hemlock, forests I've been in.

Where were you seeing this? (The streams flowing through pockets of mostly hemlock old growth forest?)