Re: SE Minnesota Mayfly Hatch Density Decline
In S.E. Minnesota from the mid 70's til today, we have lost a number of great hatches on MANY streams.
We have lost Ephemerella dorthea, Pseudocloeons, Stenonema Vicarium and Ephemerella Subvaria and Invaria & Rotunda's hatches that were once very impressive. These hatches are now very light or sporadic in most years and the Dorthea hatch is totally GONE!! Roger, what do you feel is causing the loss of these hatches? On most of the streams where these hatches were once prevalent, the in-stream substrates/habitat doesn't look any different then in years past! In other words the amount of silt in the stream bed is about the same as it always has been! The only thing that I feel has changed over the last thirty years is most of our watersheds have been tiled out and there has been an increase in row cropping of corn & soybeans!
Any ideas why we are losing our "BUGS"
Let me preface this response by saying I have no specific information about the trend of mayfly hatch density in SE Minnesota which would confirm your observations, nor for that matter, any information which would rebut your observations.
However, assuming your observations (as stated above) are essentially
accurate, my guess as to the primary cause would be a water chemistry change
detrimental to mayfly reproduction. And, one obvious suspect would (of course)
be increased agricultural use of insecticides. I would recommend discussion with
an entomologist in your state's department of ecology in order to explore the
likelihood of this being the cause.
Created: 02/17/2007 Last modified: 06/23/2007 www.FlyfishingEntomology.com