balance of ST v BT in PA streams w varying conditions

[k-bob]

Charts from Kocosvky/Carline paper ("Stream pH as an Abiotic...," 2005, no free version I see), on proportion of ST v BT in PA streams under various gradient, elevation, and pH conditions. Hundreds of PA streams in data ("N=XXX" on charts).

Interestingly, higher ST proportion at higher elevation (first chart, A = app plateau; B = ridge n valley). Due to lower headwater pH, low buffering bedrock up high, and/or ST feeding more in cold water?...

Also, much more ST than BT at high stream gradient (ST better swimmers or spawners in fast water?). Few BT once a stream is a 7-8% steep one:

 

[pcray1231]

Between 200 and 600 m (656-1968 ft) in elevation, it's interesting that while the average proportion of brook trout increases relatively steadily, the min stays pegged at 0 and the max at 100. Below 650 ft browns dominate, and above 2000 ft brookies clearly dominate.

With gradient, things don't become clear until you get greater than 4%.

Meaning, if you put elevation on a normal curve, there are trends, but there's no predictability except on the very tails of the curve.

Gradient would most likely fit a Weibull distribution (shape factor between 1 and 2, 0% being a lower bound and the peak at probably

 

[k-bob]

Yes, its complex and no none variable will do too much. But I think that the gradient info is more useful... once a section is more than 7% gradient, it's probably a mostly-ST place. I seek out streams like that, and am surprised to catch a BT, but once in a while I do. There are streams with 7%+ gradient that arent really bunched together, for ex., they are not in the same counties or the same bedrock.

The elevation chart is just another thing to consider when looking at maps to choose streams, I guess. App plateau streams at higher elevations, say 1700ft, were likely to have more ST than BT, but there were some such streams that were up to 100% BT. The DCNR geology map layer might help you guess that, 'cause pH (as influenced by bedrock) is probably involved.

Nice thing about the charts, they use elevation and gradient data you can get from maps. For pH you'd have to try to use bedrock as sort of a proxy.

fwiw, my fishing experience has been that a stream with 7%+ gradient, at high elevation, and in low buffering bedrock, is very likely hi-ST/lo BT if there are trout...

 

[greenghost]

Huh? Not sure what you just said.

ST = Brown trout?
BT= Brook Trout?

For us non-scientific types, could you translate?

Thank you.

 

[pcray1231]

Green, backwards. ST = brook trout (stands for speckled trout, I believe). BT = brown trout. PAFBC terminology.

k-bob, so statistically speaking, you have found what the data shows, which is the only way these trends can be used to predict an outcome is at the tails of the curve. Abnormally high elevation and abnormally high gradient streams which contain any trout are predictably brook trout.

That said, by seeking out such situations where browns are nearly impossible, you are limiting yourself to a very small % of the brook trout waters.

Further, your failures are in finding no trout at all. If you focus closer to the median, your failures will be discovering a nice brown trout stream.

The data isn't all that useful, if faced with a stream near the median in elevation and gradient, towards predicting whether it'll be brook or brown trout water. Those are the cases where I'd be interested in being able to predict. Partially for fishing purposes but partially out of curiosity. What makes 1 stream hold browns while a seemingly identical one holds brookies?

There is way to determine that though. Take a rod and fish it! It just doesn't satisfy the curiosity behind the cause.

 

[k-bob]

"the only way these trends can be used to predict an outcome is at the tails of the curve"

right, a stream with 8% gradient will very likely be ST more than BT. I like steep streams and ST, so that's interesting to me.

 

[troutbert]

Did the researchers discuss these questions? What were they trying to find out? And what were their conclusions?

Regarding high gradient streams, I think most of them probably have low alkalinity and pH, and that is why they are brookie havens.

There are some exceptions though, in NE PA, and probably elsewhere. Streams with waterfalls, and wild brown trout.

 

[k-bob]

The paper is about the reasons why a stream would have a relatively high proportion of St or BT. much of the focus is on pH.

the authors mention that factors such as swimming ability or spawning success, along with geology and pH differences, may be involved when one trout type is more common in steep streams, but there is no direct test of the causes in its data