The Stream Doctor

May 26th, 2003

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

Q. From Parnelli - With exotic species like the New Zealand mudsnail being introduced into ecosystems where they are not native and natural predators are absent, what ways can these new species be controlled without having to drain the swamp so to speak?

A. This is less an answer to your question than it is a general response to the problem. The short answer, and somewhat facetious, is to kill them. The problem, of course, is how to do this. Most control methods introduce their own set of problems, so until good, safe control methods are found, the emphasis must be on trying to control their dissemination into new waters.

There is an excellent article in the recent issue of Wild On The Fly entitled "Invasive Species" by Hugh Gardner. In it, he discusses the problem with exotic species that often successfully out compete native fauna for food, space, and other resources and the likelihood of eliminating, or more realistically, controlling them. I won't go into all the details about their spread, rate of propagation, etc.; you can read these for yourself.

As you mention in your e-mail, one last-ditch effort to control them is by introducing natural biological controls from their source that are not present here. This approach has its own set of problems. Although the natural parasite may be effective in the exotic species home range, there is no guarantee that the totality of environmental conditions present in the new site will allow it to act as it did previously. Will it still control the target species in its new home? Will it turn out to attack other desired species? Will the predator encounter organisms that attack it? Will it upset the new food-web in unexpected ways? The use of biological controls must be approached with caution and considerable research prior to initiation.

Given the absence of current biological controls to help control or eradicate whirling disease, the New Zealand mudsnail, the Zebra mussel, water hyacinth, tamarisk, and other plants and animals, what can anglers do? Mr. Gardner argues for greater efforts by anglers to be sure that they aren't agents for spreading these organisms by making sincere efforts to clean their equipment -waders, boats, trailers, etc. - to be sure that they are not transporting organisms or propagules to new sites.

Mr. Gardner alludes to efforts by several groups, notable the Federation of Fly Fishers, to come up with some guidelines for anglers in this battle. An interesting note is that some representatives of the travel industry say that it is not unreasonable to not only undergo stringent inspections of your fishing equipment when you travel to different countries, but in the future you may be able to bring in only new equipment! Who said this was a poor man's sport?
~ 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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