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tangledleader said:
I think that wader cleaning is worthwhile, but I remember reading someplace about how at one time there was a drainage in Colorado where the fish were called rattlin' rainbows.  The fish were so full of snails that when they would jump you could hear a clacking sound, it was the snails grinding around in their stomachs!  I wonder how much the snails would damage the fishing in most drainages, and whether or not there is a way to control the snails through natural predation.
Controlling the snails through natural predation is an attractive idea, but there are a couple of problems with it, at least in terms of the New Zealand mudsnails.

1. The snails have no natural predators in the US, and the parasites that help control their numbers in New Zealand are not present.  Introducing the parasites is risky, because of their unknown effects on the native snails.

2. Although trout are known to munch on snails, tests with rainbow trout and New Zealand mudsnails have shown that a significant proportion (higher than 25%) of the snails injested by rainbow trout pass through the gut unharmed, and alive.  Apparently their shells are pretty tough and they have the ability to tightly seal the shell opening so that the digestive juices don't get to them.

I think one of the biggest fears about the snails is that they would harm the ecosystem (and the fishing) by drastically altering the composition of the invertebrate community, and potentially monopolizing and eliminating most instream algal production.  When you get very high densities of snails (say 200,000 per square yard), they've got to eat something, and if they are eating the algae, then the mayflies, caddis, and stoneflies that were feeding on that algae have to find something else to eat.  I know there are studies underway in Montana and elsewhere trying to determine just what happens to stream ecosystems once the snails are present.  It will be interesting to see what they find out.
 
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