The Stream Doctor

May 22nd, 2006

Email YOUR Questions directly to the Stream Doctor. This is your opportunity to get an experts professional opinion on anything stream related.

E-mail message #1

I am working in Holland for a few weeks and tried to make a few local inquires about the fly fishing. One contact provided me with some information about stocking a small lake with the subject mayflies that emerge around the end of May and asked if I had ever encountered similar stocking of mayflies in a lake. Since I know very little about such actions, I am requesting that the expert and my e-mail friend respond to this question, if you have the time. If you need more information on the hatch, I will try to get this data to you before I leave Holland.

I have read in your responses about establishing population of aquatic insects in streams but did not see any references on establishing population in lakes. My question: "What is your knowledge or experience with stocking lakes with aquatic insects?"

Thank you for your time and consideration, best regards, Mike Harvell

E-mail message #2

The lake was a gravel pit about 25 meters deep at the deep end with two small springs feeding the lake. The mayflies were reportedly stocked as described by my contact's exact words (some broken English but overall very good for second language ):

"The nymphs were collected in a river about 40 miles from the lake. Actual it is very easy. Just wait a month before they are hatching, scrape the bottom sand in the river and sort the nymphs out. Put them in a recipient with wet leaves and some twigs etc. They do not need to be under water. Example: once we had them overnight in a basket with only wet leaves. When we finally released them they swam nicely to the bottom. We repeated this for 5 years. The last stocking was about 4 years ago. Last Sunday I was at the lake and discovered more than a hundred duns/spinners hanging and dancing around the trees. So, it turned out as a success."

The mayflies were classified by my Belgium contact, again in their own words: "The specie(sic) of the mayfly is the Ephemera vulgata."

This is the one of the most brazen, intriguing discoveries that I have made in my travels around the world working and learning on the side what other groups do with different fisheries. This is way beyond ku fishing in Taiwan but maybe not beyond the Cherry Salmon of Taiwan.

If you have other questions, I will try to find out more information. I want to travel down to see the lake, but I am running out of time in Holland. Best regards, Mike

Q. What is your knowledge or experience with stocking lakes with aquatic insects?

A. Well, the short answers are "zero" and "none". However, let me elaborate.

I've been asked previously about the feasibility of trying to stock insects in streams where they don't exist, and my usual response was along the lines of (1) I've never heard of it being done successfully, (2) if insects don't occur naturally in a stream and there are viable populations nearby, there is probably a good reason why they don't occur in the barren stream, and (3) arbitrarily stocking new species where they don't exist isn't always a good idea; it can cause unexpected problems.

Now to get a bit more specific about the folks in Holland who have evidently established a viable population of Ephmera vulgata by moving nymphs collected in a river and introducing them into a lake 40 miles away.

Quite frankly, this is the first episode of this type that I've heard of. I don't doubt that they did it, but I am surprised that they were successful moving nymphs acclimated to a flowing water environment into a still water environment. Perhaps the river was lake-like, large and slow flowing. This would make more sense.

I wanted to explore this, so I called some colleagues. One told me that he had read of a case where mayfly eggs attached (they're sticky) to boards, were kept wet, transported across the Atlantic on a ship, and survived and successfully established viable populations in southeastern US streams. He told me the book that he thought documented this; I spent an hour going through the book and could find no such account. I then called three aquatic entomologists located in Georgia and Florida and asked if they had heard of this story; none had, though the mayfly expert in Florida is checking the story out among his colleagues. If I learn anything further, I'll let you know.

Best wishes, ~ 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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