Saturday, November 17, 2018

Saprolegnia In The Missouri River

This isn't the first time I've seen browns like this on the Missouri. It won't be the last. It's also not unique to Missouri River browns. Saprolengnia fungus is a naturally occurring fungus found in nearly every stream in Montana and kills a number of these big spawning browns almost annually. It's sad but it's also a way that Mother Nature controls populations of fish. You can read about it here as the Big Hole saw an outbreak of this fungus back in 2014:

This particular trout was spotted with another smaller brown with the same infection last week in a back eddy near Mountain Palace on the Missouri River. The first time I had seen this was about 10 years ago. People were kind of freaking out because there were a lot of these infected browns observed. I think the presumption was that it was this horrible disease that was going to kill off every brown in the river. The shops and some of the outfitters were trying to keep it hush, hush because they didn't want it to get out that these fish--fish that people were traveling from literally all over the world to target--were all dead. The reality is that a good number of fish did die but like what happened on the Big Hole, a substantial population of brown trout survived. In fact, surveys have shown that the brown trout population on the Missouri River has remained strong even with multiple outbreaks of this fungus over the years. 

In the article on the Big Hole, it was suggested by FWP biologists that outbreaks of the disease follow high density spikes in brown trout populations. It makes sense and if true, it does support the idea that there can be too much of a good thing. People typically don't keep browns on the Missouri because they are a more coveted fish than the rainbows. Clients generally don't keep rainbows either but if someone does want to take a couple to try, I usually don't have a big problem with it. In fact, I think there is something to be said for killing a few off just to preserve the grater health of the fishery. I know that's not a popular stance for a fly fishman and an outfitter but overpopulation can lead to significant die-offs in many species of animals and apparently, those fish that we work so hard to protect as well. 

Keep 'em where they live...

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