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3. changing water level

now that i've discovered the water level pages on the usgs.gov page, it's really easy to tell when the rain has made a difference to the stream i want to fish.

so a question: if i'm expecting a hatch, will the relatively sudden rise of the water after a rainstorm affect the emergence of the bugs? do they just let go the bottom, rise however far they need to and fly off? or do they like it at a certain height? i've heard of hurricanes wiping out certain hatches because of the untimeliness of the flood.

Casey-

Interesting question. From an evolution standpoint, I would expect a given species to avoid emerging during conditions which are unfavorable for their successful reproduction.

However, conditions which are unfavorable for successful reproduction of one species, might well be either neutral or favorable for successful reproduction of another species.

Casey-


If the nymphs are mature and ready to emerge, a rise in water level after a rainstorm probably won't have any effect on whether they emerge, but it may affect where and (perhaps) how they emerge. Locations of emergence sites can change as water levels change. For some species, methods of emergence might also be affected. For example, changes in water level might have some influence on the percentage of Isonychia nymphs that crawl out on rocks to emerge vs. those that emerge in the water. Related water temperature changes might also alter the daily timing of the hatch.


Catastrophic flooding can certainly damage populations in the short term. Mostly, what I have noticed is a tendency for bugs (and fish) to get flushed out of the constricted areas of a stream into the places where the water can spread out. Some are certainly lost in the process, but repopulation usually occurs in the affected areas unless the flood has also eliminated suitable habitat.

The Brodheads had a nice hatch of green drakes (E. guttulata) prior to the catastrophic flooding caused by Hurricane Diane in 1955. Some attribute the loss of the hatch to widespread spraying of DDT in the wake of the flooding, but other hatches returned in due course. I suspect that the wholesale flushing of silt from the system eliminated most of the nymphs, but the more significant long-term effect was probably due to the disappearance of their former habitat.

I heard that after the last heavy flooding in the Little J some hatches were affected for a while, but I think they've bounced back.

Louis,

I've often been surprised by how quickly some hatches seem to rebound, even after repeated flooding. However, the rate of recovery can vary from one species to another, and significant changes in habitat can mean slow recovery or no recovery for a long time. As Roger mentioned, conditions that favor one species may be unfavorable for another. The historical changes in the hatches on some of my "home" streams are examples of this.

When I lived in the Poconos, Drunella cornuta (yes, we can call it that again) was one of the heaviest hatches on the Brodheads. Yet some of Schwiebert's writing suggests a rather different situation prior to 1955. Habitat lost for the green drakes may have been habitat gained for my favorite olive morning duns.

During my youth on the Yellow Breeches, the Hendrickson hatch that Marinaro described in A Modern Dry-Fly Code dwindled into insignificance. At the same time, we had lengthy emergences of two Hexagenia species, and the white fly hatch was in its heyday. The famous link between the white fly and the Yellow Breeches was forged in those years.

When I moved back to Boiling Springs after 25 years in the Poconos, I witnessed the resurgence of Hendricksons on the Breeches. Only the old-timers could recall the last time that they had emerged in significant numbers. Unfortunately, the Hex hatches of my youth had dwindled in number and length of emergence, and the famed white fly no longer approached the abundance that I remembered.

I suspect that these cycles of burrower abundance vs. crawler abundance probably occur in many streams as habitat changes over time. Measuring years astream in terms of those changes also makes me feel really freakin' old.

An approaching or imminent storm seems to "force" a hatch for some species, if they are close to emergence. I think this is true for at least some caenis and trico species and perhaps others. I don't think anyone has researched this. Others are displaced, of course, moving the hatch downstream and spreading it out over a wider area. Most species have upstream flight after hatch, compensating for this. There are some Caenis populations that were wiped out by the remnants of a hurricane that swept through eastern Tennessee, and the species have never rebounded, mostly because the streams were so scoured that the habitat changed and hasn't yet returned to what it was.

Long live cornuta & cornutella.

Konchu-



Was able to google the abstract of the article Gonzo must have been referring to. Is it possible for you to provide me with access to the full article? In particular, I'm wondering whether Drunella longicornis was addressed in the full article.

Roger-

Drunella longicornus is listed as "status uncertain" in Konchu's new global revision of the Ephemerellinae. Long live Teloganopsis and Penelomax!

longicornis wasn't addressed directly. if you want to discuss this, we should start another thread, rather than hijacking this one...

i believe water temp has a lot to do with the cycle and I have heard or read it may be the number of days or more likely hours of the stream at a certain temp range. these bugs will do their growing at certain temps and when the time is right and the growing is done, hatcherama. does the sun need to be out for tulips to bloom?