Re: {Tidal Potomac Fly Rodders} Re: Difficult Run

John,

I am a stormwater engineer and am quite familiar with the county's stormwater management practices and facilities. I have inspected hundreds of detention ponds in the past few years. Unfortunately the downstream fish communities are seldom considered when these are designed, especially older facilities, although the reduction in runoff and erosion is quite significant which certainly helps. You are spot on with the observation about temps. The only exception is some much larger ponds have the outflow pipe openings on the bottom of the concrete box riser structure to help release cooler water. But in a 10-20 ft deep pond there's only so much that setup can do, unfortunately.

On Thursday, April 19, 2018 at 8:53:54 AM UTC-4, John Smith wrote:

Couple more anecdotes. I actually went back to the same area in the early 90s and caught a couple brown trout (unfortunately no pics of these) so I know there were trout of some kind as late as the early nineties.

In the past, water temps in the reaches above the Hunter Mill Road crossing were very cool in the summer. We had a swimming hole up that way and I can attest to the temps being way below 80. There are considerably more housing developments now with various water retention ponds which help with runoff and sedimentation, but not temps, especially the wet ponds. They just warm things up. The upper tribs actually had very few game fish to speak of. We never caught bass of any kind or redbreast sunfish. There were bluegill, green sunfish, and a hybrid of those two in the mainstem, but we never caught them in the upper tribs. When I last fished Difficult just upstream of Tamarack, there were bass and redbreast in there. 

I seriously doubt any trout are still around, but I agree with Andrew that small populations of rare species are very hard to keep track of. One example I remember is the brook trout in Severn Run near Annapolis. They may be gone now too, but they eluded folks for years.  I haven't researched what the master plan for the basin is, but if development has stabilized there might be some potential for reintroduction to a couple of the headwaters that have the lowest amount of impervious surfaces.  Wish my commute took me past there, I would collect some temp data for a season to see for myself.

On Wednesday, April 18, 2018 at 11:57:46 PM UTC-4, Andrew Sarcinello wrote:

John, that is so cool that you actually have a picture of one of those brookies! Thanks for sharing! I can imagine it was at one time a pretty productive stream. All those tributaries would have made for a healthier population. But a highway interchange built right on the headwaters is about the worst thing imaginable for a brook trout stream.

As for the fish in the pond, the description sure sounds like a brook trout, and they have been known to survive in very low densities for long after the majority of the population is depleted. Many Gunpowder tributaries are a good example of this. There is a stream near my parent's house in PA where every few years I will randomly see a lone brook trout even though it is a very good brown trout stream and electrofishing surveys have never turned up a brook trout. They are quite good at finding a way to barely hang on, and I actually don't think road crossing themselves are a death sentence to these fish because the deep culvert pools can provide refuge when stormwater impacts have wrecked literally every other potential hiding spot on the stream.

Interestingly, the USGS gage on lower difficult run has a water temp reading. Last year it peaked around 80. While that is harmful to brook trout reproductive health it is not definitively lethal, though it's close for sure. Imagine that the headwaters and tribs are a couple degrees cooler and now you're talking about something they can certainly survive, though with a lot of stress.  Now, whether there is suitable spawning substrate and in stream cover for them to sustain a population... doubtful.

I wouldn't say it's totally impossible for there to still be a few brook trout hidden in there somewhere, but I do think it's extremely unlikely. If the fish seen in the pond was indeed a brook trout, there's always the possibility it was brought in by bucket from some mountain stream. And, of course, maybe it wasn't a brook trout at all.

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