The Stream Doctor

February 5th, 2006

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Comments: I just read your article in about stocking aquatic insects in new waters. I can't see why it should be difficult to do if the waters are of similar size and water quality. Forty years ago my dad, my brother and I were driving home from an evening of fishing the big mayflies (Ephemera guttulata) in Penns Creek and stocked some of the big flies in a very casual manner.

We always fished the live flies ... putting one or two on a light wire #12 hook and gently swinging them just upstream of rising trout. We collected flies from the underside of tree leaves along the stream to be sure that we had enough bait even as the evening turned from light to darkness making it hard to fumble around looking for new flies. We stored our flies in light plastic or cardboard boxes or cans.

On the evening in question driving home from the creek, along a small mountain brook, we passed a low dam on the brook that impounded perhaps three quarters of an acre of water. As we drove by the pond we realized we had failed to empty our bait cans at the creek and so we flicked their contents toward the pond and drove on with nary a thought as to the consequences.

One year later, same time, same place, we drove into Penns Creek again and were surprised and pleased to see hundreds of big mayflies in the air and on the water of the small pond. Brook trout were feeding actively all over the pond. We chuckled to ourselves and complemented each other for being such clever fishermen.

That was the last time we saw the mayflies on the pond. I suppose the adults we saw mated and laid eggs but somehow the muck on the pond bottom was not suitable for their continuance. We've never tried to stock it again.

But I asked Joe Humphries if he had ever tried to move the big flies to Spring Creek between State College and Bellefonte here in Pennsylvania. It's only thirty miles from Penns Creek to Spring Creek. The flies were in Spring Creek by the millions prior to the massive oxygen deficit in 1955 caused by the opening of a new, bigger sewage treatment plant for State College that was /not/ built with tertiary treatment. The resulting load of secondarily treated sewage eliminated all insects and fish for many, many years until a new tertiary plant was constructed. I haven't fished Spring Creek but they tell me the fishing is excellent however you're not supposed to kill and eat any fish (that has to do with MIREX contamination, not sewage).

Anyway, Joe said yes they had tried but it didn't work. I can't imagine why. The water quality is essentially the same and the big flies /used/ to be in Spring Creek. I wonder if Joe got the right flies. You'd need to select the fertilized females and ignore the just emerged females and all the males. Should be easy. The sexes and their instar status are easy to distinguish. I always think that I should do it myself but I live a hundred miles away now and you'd need to collect hundreds of flies and do it over at least three days to assure good coverage. I'd need accomplices.

If ever there was a place to try successfully to transplant mayflies the Penns Creek to Spring Creek saga should be it.

Richard W. Wahl
Professor Emeritus, Biology
Shippensburg University of PA.

Responses: Thanks for your thoughtful note. You bring up several points and I'll respond accordingly. But first I need to be forthright about one thing: I'm an ecosystem (stream) ecologist and not an entomologist, although I've done a lot of work on aquatic insects. Thus, some of my thoughts below are in the realm of "educated guesses"; you'll recognize these I suspect.

First, let me address your release of mayflies into a brook and the subsequent observance of a significant hatch a year later. This brings up a couple of subjects: (1) introductions into foreign habitats, and (2) were the mayflies in the subsequent hatch yours?

Introducing species into environments where they don't occur (and we really don't know this in your case), has resulted in many tragic and unwanted consequences, and I think you acknowledge this when you say, "...with nary a thought as to the consequences." I'll give you the benefit of the doubt. Think of the lake trout in Yellowstone Lake, rabbits in Australia, kudzu in the southeastern US, brook trout eliminating native cutthroat trout in western streams I could go on, but I'm sure you get my point. Conversely, there have been successful and desired re-introductions, e.g., the wolf in Yellowstone, the lynx in Colorado. However, the latter are re-introductions of native species into former habitat, not introductions into new habitat where they didn't occur. There's a big difference. Sermon over.

Now let's address your apparent successful introduction (or was it?). You say that there were "..hundreds of big mayflies in the air and on the water..." Were these a result of your releases? Let's do the math, as they say. You didn't say how many insects you released, but I wonder how many of them were gravid females ready to lay eggs, and how many were healthy enough to oviposit after being carried around in boxes. I find it hard to believe, and this is a guess on my part, that the number of gravid females healthy enough to actually oviposit was very high. Then we have to factor in natural mortality to the eggs and subsequent instars during the year prior to the emergence you observed. I'd be surprised to find that your minimal introduction could result in such a hatch as you observed. Species of the genus Ephemera have a one-year life cycle; did the hatch occur in subsequent years? I think a more plausible explanation might be that the mayflies were already there and your return coincided with a major hatch.

Second, let's talk about why or why not re-introduction of this species has not been successful in Spring Creek. Notice that I said "re-introduction" not "introduction." If the species were present in Spring Creek prior to the construction of the sewage treatment facilities, it tells us one significant thing: conditions in Spring Creek at that time were conducive to existence of the species. That's important. The failure of Dr. Humphries to successfully reintroduce the species implies two possibilities: (1) he simply couldn't move enough insects to reestablish a viable population, or (2) environmental conditions are not suitable for existence of the species. I cannot address the first possibility because this would need input from Dr. Humphries and input from population entomologists as to how viable this approach is; I'd love to hear this discussion. The second possibility needs serious consideration. Thirty miles is not too far for caddisflies to fly; there are numerous examples in the scientific literature on this subject. Further, though I'm postulating here, they may not have to migrate the full 30 miles; other populations of E. guttulata may occur in intermediate, suitable habitats closer to Spring Creek. This means recolonizers may have even less distance to fly. The point is, that whether viable adults reach Spring Creek from Penns Creek, Dr. Humphries' transplants, or intermediate streams, they apparently can't survive there. This tells me one important and conclusive thing: some physical, chemical, or biological condition is present in Spring Creek that wasn't there previously, and that this factor, or combination of factors, prevents the existence of the species in Spring Creek. I wouldn't hazard a guess, but it could be quite subtle or even something as obvious as the MIREX concentrations.

One other point. I'm not familiar with the geography of Spring Creek and where the perturbation occurred. Let me make the assumption that the sewaage facilities in State College are below the headwaters and that there is an unperturbed reache of Spring Creek above the facilities. If this is true, it brings up a question: Do the mayflies still occur and emerge above State College? If so, certainly their is a population present that could and would recolonize the downstream reaches via drift and flight IF conditions were suitable. Further, if they occurred above State College prior to installation of the plant, what happened to them? A downstream oxygen depletion and other polllutants shouldn't impact the upstream population if it were present. If no upstream population was present, I'd have to ask, "Why not?"

Sincerely, ~ Bert

If you have a question, please feel free to contact me.
~ C. E. (Bert) Cushing, aka Streamdoctor
105 W. Cherokee Dr.
Estes Park, CO 80517
Phone: 970-577-1584

The 'Stream Doctor' is a retired professional stream ecologist and author, now living in the West and spending way too much time fly-fishing. You are invited to submit questions relating to anything stream related directly to him for use in this Q & A Feature at

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