Stream reaches Class A equivalency with large increase in biomass

M

Mike

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My crews and I surveyed a roughly 3.8 mi Lehigh Co stream section in 1983 and again in 2014. During that time period the wild brown trout biomass average at the two sampling sites jumped from 14 kg/ ha to 101 kg/ha., based on preliminary calculations. What an improvement.

I am very familiar with this drainage basin and land use has remained the same. It appears that this improvement is once again tied to riparian vegetation maturation. Erosion and sedimentation are still substantial, this in large part because the stream cuts through legacy sediments from former mill dams.

Relatively minor stockings by a local club have occurred throughout the period, which apparently has not harmed the wild trout population to any great extent' if at all, and has kept lands open to fishing.

Many thanks to the Message board regular, who brought what he thought was a substantial increase in the population to my attention. His observations of wild trout streams in the past have earned him "stream cred," which in part precipitated a re-survey.
 
More good news from the wild trout front - good to hear.
 
Love hearing good news like this. While I always prefer native brook trout, better wild brown trout than no trout at all.

Jeff
 
Mike, that's a huge gap in the survey dates. Is there any other evidence that the stream biomass doesn't fluctuate significantly based upon shifting environmental factors? I'm ignorant, but is it possible that a stream can have low biomass one year and high biomass the next and return to low and back to high, etc. in short time spans? Or are the observation made 31 years apart truly indicative of an improvement trend?
 
Warms my heart to hear.
 
Jack, environmental issues such as floods and droughts will cause a drastic drop in population, but it is rare that a population recovers quickly, I won't say it doesn't happen, but it would be unusual. All it takes is one good year class to survive and a population can rebound quickly.
But if you look at the surveys you see it's not usually happening that way. A very poor population in a Berks County brookie stream became a Class A stream without anyone knowing it had until fished it for only the second time. It has since dropped in population, but may now be rebounding, but it's taken several years to show any sign of recovery.
 
Seems like the trout is doing allot better than the smallie these days when about five years ago I thought smallies were going to be taking over allot of ours streams due there higher tolerances of pollution and climate change while quite the opposite is happening . I guess I was wrong.... But I appreciate these posts Mike its always good to hear good news about our streams when most of the time we are hearing the bad news.
 
The question is reasonable. Populations vary. Even this population varies depending upon where it was sampled. You'll note that I said average biomass. The downstream site's biomass was around 80 kg/ha and the upstream site's biomass was around 120 kg/ha.

Varying by the amount you suggest, from 14 to 101 kg/ha and back again would be highly unusual and would most likely point to a localized acute or chronic ecological or environmental problem that had a direct impact on the stream's trout population. I would expect natural variations off the top of my head to not be more than 50% without such a problem once a limestone influenced brown trout stream becomes suitable enough to support the high biomass that we found. Something has changed for the better to allow that biomass to reach the century mark, which is pretty lofty.

If you work your way through some of the regional biologist reports and archives thereof on the PFBC web page,you will find some limestoners with long-term data sets. Looking at those tables you will see how much the biomasses have varied from year to year. I have not done so (looked at those tables recently), but when I have participated in multi-year surveys on limestone brown or limestone influenced brown trout streams I don't recall tremendous variations in biomasses once high biomasses have been achieved that, for instance, dropped one of these limestoners or limestone influenced brown trout streams out of the Class A category.

The one exception that I can think of, if I am recalling correctly, is directly related to the impact of stormwater runoff widening the stream and reducing the sizes of pools and the quality of the habitat. But the stream(s) did not fall below Class A.

 
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