Trout size

[marcq]

Why do some trout streams have a higher population of large fish yet others tend to have a lot of small ones. genetics / Stream conditions / availability of food. What are the driving factors that make large trout?

 

[redietz]

Predation. Thinning the population prevents stunting. I've read in several places that the reason New Zealand produces such large trout is that every river has eels which keep the trout population in check.

 

[gulfgreyhound]

Not all rivers in New Zealand have eels. Isolation, lack of competition, genetics, lots of food, and predation by larger fish make for some monsters in NZ. Less fishing pressure helps and lots of trout are sea run browns which benefit from a bigger food supply in the oceans..
https://www.completeangler.co.nz/info/twizel-tekapo-canal-html-13
https://www.bing.com/videos/search?q=lake+tekapo+canal+fish&view=detail&mid=ADF918F688BC8ACCBA1EADF918F688BC8ACCBA1E&FORM=VIRE
GG

 

[troutbert]

Physical habitat: Depth and cover.

Where the habitat is very good, trout can live long enough to get big. They can survive through droughts, scouring floods, and escape predators in such places.

Even on freestone streams, which people think of as only holding small trout, browns can get over 20 inches.

Where the habitat is very thin, it's not conducive to producing big trout.

 

[TJones]

I definitely think genetics must play some factor, some of our streams just have more large fish than other streams... considering habitat, food, fishing pressure and all that.

 

[troutbert]

Low levels of fishing pressure helps.

 

[wbranch]

marcq wrote;

genetics / Stream conditions / availability of food.

Yes all of your comments contribute to some waters having larger trout than others.. Add to that rivers with more or less stable flows not affected by spring high water events or summer low water conditions. Furthermore waters with a narrow temperature range will grow bigger trout if that range is in the more ideal temperatures of 52 - 62 +/- a few degrees. High concentrations of aquatic insect life and forage fish all add up to grow larger trout.

 

[krayfish2]

When reading the OP question, I immediately went to the same place Matt did...temps and flows.

The more I think about it, you probably have some genetics in play but I'd expect forage base, consistent flow / temps and deeper hold water for protection from predators are also important. With that said, marginal water seems to grow giants....which brings back the topic of transient trout that move in and out of "trout water"

 

[marcq]

Ok I have a scenario I wanna throw out there hypothetically speaking.

Take a stream like valley creek. A healthy stream. Stable water temps. Tons of mostly sub 12 inch fish. Lots of scuds and nymphs.

Now you go to a stream like the Lackawanna. Recently I’ve been intrigued by this stream do to the fact it holds large fish. Probably not as healthy of a stream water temps much warmer and not as many bugs. The fish become predators hear.

Are these fish the same? They are both brown trout. Are there different sub species? One that becomes more of a meat eater? If you took a valley creek brown and threw it in the Lackawanna would it become a large meat eater if it didn’t get eaten and if you took a Lackawanna brown and threw it in valley would it become a bug eater or go and wreck havoc on the small brown in valley creek?

 

[troutbert]

Valley Creek has mostly "thin" habitat, i.e. riffles and pocket water, but not much really prime pool habitat.

The Lackawanna has numerous large pools.

 

[ryansheehan]

To me food source is the number one factor. I feel like the reason I catch big browns in marginal trout water(tempature wise) is the abundance of forage that can support their needs. There are certainly many factors but I would rate this as number one.

 

[JackM]

ryansheehan wrote:
To me food source is the number one factor. I feel like the reason I catch big browns in marginal trout water(tempature wise) is the abundance of forage that can support their needs. There are certainly many factors but I would rate this as number one.

Food, food and food.

 

[afishinado]

troutbert wrote:
Valley Creek has mostly "thin" habitat, i.e. riffles and pocket water, but not much really prime pool habitat.

The Lackawanna has numerous large pools.

+1 above.

The Lackawanna has big fish habitat throughout the river. Deep dark holes, pools and runs. And many of these areas are lightly fished and some almost never fished.

Valley Creek is a shallow creek without a lot of big fish habitat.

 

[troutbert]

I watched a PFBC crew electrofish survey a section of Young Womans Creek.

They surveyors would say what size of trout they expected to get in a particular place, just by looking at the habitat.

If it was thin water (shallow, not much cover) they'd say something like "2 to 5 inches", and that's what they'd get.

Then they'd come to a run that's a little deeper, with a bit more cover, and they'd say "6 to 10 inches" and that's what they'd find.

Most of the 300 meter stretch as pretty "thin" so they got trout that were modest in size.

Then at the end of the 300 meter stretch, they came to a place where the stream took a sharp bend. At the outside of the bend the stream had undercut tree roots, and the trees were leaning over the water, and woody debris had caught on those and accumulated. The depth was about 3 feet, even in low flow conditions.

So it had the two key ingredients: Depth & Cover.

They said something like "Here we'll see some good sized trout." They paused to make preparations then went in there, and there were nice-sized trout flying around all over the place. They got several 14 to 16 inches, and a bigger one escaped under the tree roots and they estimated that one at 18 inches. They said the in the past at the same spot they had found a 21 incher.

The "thin" sections and this "honey hole" are right next to each other. The one has 8 inch fish, the other has 18 inch fish.

The genetics aren't different. The food supply coming down the creek isn't different. The water temps aren't different. Neither is the base flow. Or the ph and alkalinity. Or the amount of pollutants.

Everything is the same except for one factor: The physical habitat.

 

[Dave_W]

Agree with the above, especially habitat as a factor.

Regarding the "marginal downstream areas hold big trout" theory (which I agree with): Remember, it's only "marginal" with respect to temps - habitat, depth, and cover, are often much better. Angling pressure is often lighter.

In my rock rolling and other observations I have found very consistently that warmer waters are richer and have more food biomass and diversity. When I survey upstream areas I often get a lot of macros but they are predominately small and heavy with a particular species, such as scuds or caddis. Minnows and baitfish are less noticeable. When I move downriver, often below what is considered trout water, I get more bugs but they are more varied in species and bigger - lots of stoneflies, march browns, etc. Moreover, baitfish are much more prevalent and I see schools of shiners, chubs, fallfish, darters, juvenile suckers, etc.

Where would you live if you were a 20" brown trout?

 

[ryansheehan]

troutbert wrote:
I watched a PFBC crew electrofish survey a section of Young Womans Creek.

They surveyors would say what size of trout they expected to get in a particular place, just by looking at the habitat.

If it was thin water (shallow, not much cover) they'd say something like "2 to 5 inches", and that's what they'd get.

Then they'd come to a run that's a little deeper, with a bit more cover, and they'd say "6 to 10 inches" and that's what they'd find.

Most of the 300 meter stretch as pretty "thin" so they got trout that were modest in size.

Then at the end of the 300 meter stretch, they came to a place where the stream took a sharp bend. At the outside of the bend the stream had undercut tree roots, and the trees were leaning over the water, and woody debris had caught on those and accumulated. The depth was about 3 feet, even in low flow conditions.

So it had the two key ingredients: Depth & Cover.

They said something like "Here we'll see some good sized trout." They paused to make preparations then went in there, and there were nice-sized trout flying around all over the place. They got several 14 to 16 inches, and a bigger one escaped under the tree roots and they estimated that one at 18 inches. They said the in the past at the same spot they had found a 21 incher.

The "thin" sections and this "honey hole" are right next to each other. The one has 8 inch fish, the other has 18 inch fish.

The genetics aren't different. The food supply coming down the creek isn't different. The water temps aren't different. Neither is the base flow. Or the ph and alkalinity. Or the amount of pollutants.

Everything is the same except for one factor: The physical habitat.

Troutbert, I would say the trophy fish occupied those places because they have grown big . I would not say that those fish became big because of those places. Those large fish have not occupied those prime lies their entire life. They started in the thin water, then moved to a little deeper run and so on. As long as there was enough food for them to grow they would continue to move up in the pecking order. If there were limited food sources the trout in the most prime lies would not be that big. I've seen enough large fish in small spring creeks that are easily seen from overhead to make me realize more that cover is not the most important aspect. There are certainly many factors but take away food and nothing else matters.

 

[Canoetripper]

I can't disagree with any of the above posts, especially about the habitat and cover. That said, the two places where I have caught large trout(Alaska and the Frying Pan River in Colorado), abundant food has to be a major factor.

In Alaska, there are all of those salmon eggs and very young salmon. In the Frying Pan River, there are all of those mysis shrimp released from Reudi Reservoir.

What I learned about the Frying Pan River is that those mysis shrimp don't live very long when they exit the reservoir and because of that there are two different flies available at the local fly shops. Those that exit the reservoir right away and those that die on their way to the Roaring Fork River.

That is a lot of easy protein coming right to those trout.

 

[RLeep2]

My vote, particularly in the type of streams like Young Woman in Troutbert's example, is that habitat is primary in the production of larger fish. So long as the forage base is adequate, habitat matters most, IMO. I'm skeptical this dynamic changes much, if at all, when the forage base is exceptional as opposed to simply adequate. Habitat is still the primary driver.

 

[afishinado]

RLeep2 wrote:
My vote, particularly in the type of streams like Young Woman in Troutbert's example, is that habitat is primary in the production of larger fish. So long as the forage base is adequate, habitat matters most, IMO. I'm skeptical this dynamic changes much, if at all, when the forage base is exceptional as opposed to simply adequate. Habitat is still the primary driver.

Agreed ^

A stream with an excellent food source, but lacking good habitat will not grow very many bigger fish.

Big fish habitat holds.........big fish!

 

[larkmark]

`I wonder about what changed on Spring and Penns? the habitat seems about the same for many years. It seems to me that 15 yrs ago there were way more fish in the 13-20" range. Now I rarely catch any much longer than my hand. I know there are some bigger fish there but not nearly the numbers. There are a lot of fish but mostly small. I noticed this year there were loads of hot dog length fish in the Delaware too.