Wednesday, March 16, 2011
Stream Report: The Lynch River
The Lynch River flows through the northern part of our county (Albemarle), and I've been told that it used to be one of the best trout streams in the state -- not the case anymore. It does have good populations of mayflies and stoneflies, and like some of our other "good" streams, in the winter it is overrun with black flies. As I looked down today at the rocks in the water, there were very few without strings and patches of black on them -- colonies of black fly larvae.
As I went about lifting rocks -- with my gloves and boots soon covered with the squirmy black things! -- I saw lots and lots of small minnow mayflies, and a fair number of Epeorus flatheaded mayflies. The Lynch, like the Doyles River, is a stream where I expect to see this genus of flathead -- and only this genus of flathead -- this time of year. I left them alone, though I did put on in the tray for a photo.
On the small minnow mayflies -- they were all genus Baetis, but as I did yesterday at the Doyles, I found two different colors: some were the normal olive green that we've come to expect, others were totally black. Both types were mature (large wingpads), both had two tails, both had metathoracic wingpads -- i.e. both were Baetis in genus. But look at the difference in color:
The black one (with a brown head):
And the green one (with black = mature wingpads):
I don't recall seeing these "totally" black small minnow mayflies before. I assume this different color is a matter of "species" -- but I don't know for sure.
So the rocks were covered with black flies, lots of small minnow mayflies, a fair number of flatheads (all Epeorus), and I also saw a couple of Strophopteryx large winter stoneflies crawling around. All of the stoneflies I found were in leaf packs.
Because the heavy rains of last week really flushed out the streams, the leaf packs were not that many. Still, there were some close to shore, so I took a look. I looked in two leaf packs -- one had 6 Clioperla Perlodids in it, the other had 8! I've never seen so many Clioperlas in one place together. And they were all large, all mature. I picked up a couple for pictures, then scrambled to grab the others and get them back into the water before they got confused and ran off into the woods! Have a look at one of these beautiful insects:
What a magnificent creature! Hard to beat colors like that (Don't forget to click on the photo to enlarge it.) And take note of the light colored dots on the abdomen while I read from Peckarsky, et.al. (Freshwater Macroinvertebrates, p. 73) on the final key to Clioperla identification: "Dorsal abdominal segments uniform, brownish, except for a few small light spots (which may be in longitudinal rows)." Here we've got a "textbook" example! (Also notice how the outer edges of the first pair of wingpads -- those closest to the head -- run parallel to core length of the body, while the outer edges of the second pair of wingpads angle away from it. This is one of the ways we identify Perlodid stoneflies.)
I also found Diploperla Perlodids and Isoperla Perlodids, and just as I found yesterday, the Clioperlas were fully mature, the Diploperlas were mid-size (shall we say "juveniles"), and the Isoperlas were babies. Sort of like "papa bear" "mama bear" and "baby bear" -- if you will.
Finally, I found one Giant stonefly in one of the leaf packs -- and it was a "giant" (approaching 2" in length). Below are the dorsal and ventral views: note the "thoracic gills".
Oh. I did not find any spiny crawler mayflies or any brushlegged mayflies. I'm sure they're here since the spring samples I've done here in the past with StreamWatch have been loaded with them. I suspect it's simply a matter of where I looked in the riffles. (If you're someone from StreamWatch who's reading this blog, by the way, I never go into the riffles in which StreamWatch samples when I'm out on these excursions. I always find my own riffles. Not to worry.)