Rainbow trout: sensitivity limits reproductive success in Pa/adult survival

[Mike]

The subjects of limited RT reproduction in Pa and temperature sensitivity come up periodically here. Yesterday, I happened to be doing some research and stumbled across two scientific publications that refreshed my memory. Here is the long and short of it:

Primary limits on reproduction: Water temps that are too warm (higher than 56 deg F) or too cold (42 deg F or lower) limit or prevent reproductive success, despite the fact that RT adults survive quite well at higher temps. These temps that affect reproductive success fall well within the range of typical Pa freestone temps, but not limestoner temps near their source. Eggs will not develop normally in the fish if constant water temps of 56 deg F or higher are encountered. Temps not exceeding 54 deg F are preferable for a period of at least 6 months prior to spawning. How many streams in Pa do not exceed 54 deg F during the summer? Likewise, excessive losses of eggs occur during incubation in the redds if temps fall below 42 deg F. Think about Pa winters, which explains why fall spawning of Pa rainbows is not a good strategy.

This does not necessarily explain two streams in the Allegheny drainage, but to my knowledge those are the only two freestone exceptions with substantial multiple year classes of fish that have been found in Pa. and I don't have enough knowledge of those to express an opinion as to the local effects that allow them to be exceptions. Additionally, I don't know whether or not they still support wild RT pops. I think, however, that the first paragraph above provides good guidance with respect to what the problem probably is with RT reproduction in Pa.

Warm RT fisheries: As for adult RT survival and fishing, one study of a formerly very successful fishery in which water temps over the years gradually increased due to urbanization revealed that water temps that exceeded 68 deg F resulted in substantially more mortality than did the C&R fishing that was occurring over those fish during those warmer water temp periods. The fishery declined. So water temperatures alone, just like the ones we see annually below Blue Marsh Dam during the summer in the Tully DH Area, were enough to cause considerable mortality.

 

[Chaz]

Good stuff Mike, as always very informative, We appreciate the science.

 

[Architeuthis]

I fish one of the Allegheny freestone drainage's your talking about. 75% of that stream requires a nearly impossible 1/4-1/2 mile hike down a rocky hill through posted land to access. Lots of heavy tree cover and fairly deep (considering stream size) highly oxygenated water that was in the high 50's in July last year. It's a great little stream that thrives due mainly to the lack of easy angler access I would guess.

 

[geebee]

interesting - so spring spawning is preferable. how do those temperature limits compare to ST, BT etc I wonder ?

 

[MHanes]

the one stream that is on the PFBC commission class A list in the allegheny drainage does support multiple year classes of rainbows still. I fish it often and my guess is that is has to do with a good abundance of springs entering the section of water but thats just a guess.

 

[troutbert]

Aren't there decent numbers of streams with wild rainbows in other eastern states, both to the north and to the south of us?

And if so, how does that fit into the water temperature hypothesis of why there are few wild rainbow populations in PA?

 

[Mike]

Troutbert,
My recollection is that the southern explanation is pretty straight forward. Isn't Pattee Library right up the road from you?. Let us know what you find out.
Mike

 

[laszlo]

A 56 degree constant temperature for 6 months is hard to obtain except where the source is a lake and the water release is pretty constant. A stream that fits this description is the Codorus. While it seems to have a healthy community of BT, has fingerling RT ever been considered?

 

[The_Sasquatch]

Hard to believe that those Smoky Mountain streams hold that temp long enough!

 

[RLeeP]

This topic has always been of great interest to me and over the years, I've tried to learn as much as possible about the whys and why nots of wild RT pops., particularly in PA freestones.

Back in the 90's when I was living in Tionesta, Ron and Al were gracious enough to let me poke around in the Area 2 files as much as I wanted, so long as I let them know ahead of time and cleaned up after myself... I found a lot of interesting information about wild RT pops, particularly in the ANF and nearby areas. Basically, based on what I read in the files, there is (or was up until that time) a fairly long term history of pretty low biomass, but sustained ("stable" being perhaps too strong of a term) wild rainbow populations in a surprising number of streams in the area. Whether these pops were the result of direct access to the Allegheny (most of the streams were direct Allegheny tribs or first order tribs to direct river tribs) or the result of whatever strain of RT the Feds were using when they did the ANF stocking, I don't know. I've always suspected the latter, but have no supporting evidence based in a comparison between strains of RT.
Anyway, as I recall, there were at least 10 and perhaps more ANF or nearby streams with sustained RT populations. Some were in ATW's and others were in streams that had never been stocked. In most cases, the rainbows were the junior partner in sympatry with brook trout. I fished four or five of these streams and while it sometimes took a while, I always found some 'bows. For all I know, these pops. may all be gone now (acidification and being overwhelmed by the more acid tolerant brookies), with the exception of the two well-known current populations.

I found the entire topic intriguing at any rate.

So far as sending Dwight to the library to look into wild RT in other northeastern states, that's really not necessary. Here is a listing from NY-DEC for some of their streams in the Genesee, Lake Erie, Chemung and Allegheny drainages listing nine (I think I counted right) streams with (evidently) stable wild rainbow fisheries: http://www.dec.ny.gov/outdoor/29286.html

 

[streamerguy]

MHanes, interesting you mention the springs. But then again lots of other streams in that area have plenty of springs as well. It's gotta be something other than water temps, I've caught many year classes of bows in the two main tribs as well as the stream they feed and the temps of course vary by stream. Maybe there's something unique water chemistry wise in that watershed? Either way it is a unique watershed, one of my favorites, and not just because of the bows 😉

Anyone have any info/theories on the Laurel Highland populations?

 

[pcray1231]

There are at least 5 in the upper Allegheny drainage, not 2. And no, they aren't all in the Hemlock drainage. I suspect there are still more as RLee states was the case. I don't get up there enough to keep searching.

And there are a bunch of freestone streams in the laurel highlands with them. Really, I'd guess that more freestone streams contain wild bows in PA than limestoners, and it might not be close. If I had to hazard a guess I'd say we likely have 30+ freestoners statewide, though they do tend to bunch together in certain regions.

Many smallish freestone streams do stay pretty cold. I've measured 55 in mid summer.

Also, rainbows dominate the apps in the southern range. North Carolina, Tennessee, Georgia, etc. Including in areas that get far warmer than your typical PA wild bookies streams. 2 summers ago in August I was catching PA brookies in 60ish degree water. 2 days later I was catching wild bows in Tennessee, in numbers, in 67 degree water.

In fact, down there, the bows are considered the dominate wild species in marginal waters like browns are here. As you get way up to the high elevations where it stays cooler, brook trout become more abundant.

It could be a case of different genetic strains.

 

[salvelinusfontinalis]

I know of at least 3 wild rainbow trout streams in sepa with established populations. 2 freestone and 1 limestone.

 

[Mike]

The answer is consistent with what I said in my initial post, which is what I suspected based on logic, but needed to verify before discussing the southern waters. It also turns out that the explanation for the freestoner RT reproduction is the same in western Pa as it is in the south. In the 1930's federal spring spawning RT were being stocked. The aforementioned populations in W Pa and in the south are spring spawners; therefore, the water temps during egg development in the females are not problematic.

 

[geebee]

laszlo wrote:
A 56 degree constant temperature for 6 months is hard to obtain except where the source is a lake and the water release is pretty constant. A stream that fits this description is the Codorus. While it seems to have a healthy community of BT, has fingerling RT ever been considered?

Cordorus creek has a class a section below it so I'd guess not.

Fingerlings are stocked below the dam on the tully. I don't know if the same is true for the pohopoco below beltzville ?

 

[Mike]

In the late 1980's or early 1990's, there was a substantial population of reproducing RT in Codorus . That population later diminished such that wild RT were a very minor component of the trout population. There are occasional wild RT in the Tully DH Area....perhaps one for every 100 yds Electrofished near the cooler inflow of Cacoosing Ck, which is a Limestoner.

 

[Chaz]

I may be wrong but there was a small rainbow population in Codorus Creek at one time. As an example, of what happens in these streams at least in Eastern PA is that condition change from year to year in the streams and when they do rainbows take advantage of the conditions. Some streams have reproduction of rainbows for a few years then the rainbows disappear and the browns and brookies are left.
I think we've seen more of it over the period that PFBC was buying bows from NC Hatcheries. I think the reason was that the NC fish were spring spawners more closely related to the original strain of wild bows from the Sacramento R. or someplace else out west. The curious thing is that Big Spring has both spring and fall spawners, most likely the result of the constant flow of cold water from Big Spring, which is 54 to 56 degrees.
The Little Leigh has a small population of wild rainbows, but conditions there aren't as constant as Big Spring.
All trout streams whether they are limestone streams or freestone stream have cold water springs, the difference is in the chemistry and volume, with volume being the key.