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Adventure568

Very weird smallmouth fishing

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I was fishing the housatonic river here in connecticut on Saturday and the fishing was EXTREMELY slow. My dad, my friend and I each caught about 5 fish. Usually we catch about 20-50 fish per person. The river wasn't too high, just a bit muddy. After further inspection of some spots on the river, my friend and I found huge amounts of dead crayfish and a few dead fish. We found a dead rock bass and a small dead carp. The smallies just were not biting at all and the ones we did catch we all under 10 inches. Although, I did catch a 12lb carp which fought very well, like a normal carp should. It seemed like the smaller the fish the more affected they were by this phenomenon( I guess you can all it that) no one else pulled in anything, and there were not many bugs out at all. We thought it had to be something in the water or something to do with the summer solstice. We never had a worse day than this on the river before, it puzzled all of us. The river was at near perfect flow, we had sun and high pressure, and just a little mud. Any ideas on what went wrong or why this happened? Any help or insight is greatly appreciated

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Anoxic fish kills are common in ponds in the summer, especially after the first big rain event, but not as likely in a river. If it had been anoxia (low dissolved oxygen) there would be more dead animals than just crayfish. Sounds suspiciously like something toxic, which should be reported to the state environmental agency. It's often hard to pinpoint a cause long after the fact, especially in rivers, but to be safe, I wouldn't eat anything you caught, and I'd wash thoroughly in case you handled anything. Single species kills usually are not oxygen related. If there are dead mammals or amphibians, it's almost sure to be toxicity.

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If it were me... the first item I'd wonder about is the water temperature where you were fishing... since it's that time of year. What I don't know is whether water temps are the problem up there that they can be where I am in Florida. I'll be interested to hear what others have to say.

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Temp can cause kills, even in Fla., but it would kill more than just crayfish.

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Crayfish are bottom feeders, generally. An algae bloom could be to blame.

Once the bloom dies off, it all falls to the bottom. The crawdads eat that, fish eat them, the whole food chain can be killed. Fortunately, not all (of any level) of the chain is eating the same things on the same day, so there are always survivors. In some cases, the kill actually helps the survivors by thinning the competition.

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That's why rivers are different. Ponds, especially in southern states, and those in fertilized areas (i.e., farming, or urban residential) tend to produce too much algae. Partly it's decomposition that leads to oxygen depletion, but also algae not only produce oxygen while the sun is shining, but they also use oxygen, day and night for respiration. Algae don't provide enough oxygen to supply the whole ecosystem... most DO usually dissolves from the air through the water surface (especially where there is turbulence). Excess algae can result in DO getting up into supersaturated levels during the day, but dropping to zero during the night. That tends to result in mass fish kills, but even when DO is not low enough to kill fish, it can still eliminate the benthic organisms.

 

Streams are usually well aerated due to the current, and algae don't generally reach high levels because they are constantly drifting downstream. They sometimes reach high levels where the stream widens out near the mouth, so that flow is reduced.

At any rate, even if we were talking about toxic bluegreen algae, they would affect many other benthic species as well, such as caddis larvae, etc. About the only thing that survives low DO episodes are chironomid larvae, and for that reason highly eutrophic lakes have huge midge hatches. Not only are they equipped to survive low DO, their predator organisms are greatly reduced.

If all these dead crayfish were all in one spot, I'd suspect someone dumped them. If they are generally distributed, something else is at play, but with water temp of 70 deg and stream flow, I would rule out low DO.

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I was thinking along the lines of toxic algae. Since the Red Tide episodes are relatively frequent here ... that's what comes to mind for me.

We do have lakes, like Lake Apopka, which are pea soup with algae ... but that algae supports hugs numbers of Threadfin Shad, and the crappie and bass populations are well fed.

 

Anyway, it was just a thought.

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The crayfish are always piled up in one spot in the river, it is a series of pools. Usually I see about 10 dead ones on a regular day but I saw about 100 on this day, and there almost no algae in these pools

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That's a horse of a different color! Small shallow pools and even shallow sluggish streams can get over heated during the daytime... at least they do in Fla. The solubility of oxygen in water is inversely proportional to temperature... hot water doesn't hold much or any oxygen (or any other gas). Were the pools isolated?

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I've seen instances in several places of -what seems to be- abnormally high numbers of dead crayfish. USUALLY this is around the period of molting, which at least around here (Pennsylvania) is about now--- mid/late June through July. Crayfish are more vulnerable to everything when they are shedding. Quite a remarkable percentage of the population dies during the process. The bottom stretch of the Yellow Breeches creek is one place where every year starting about now you can go and end up saying "Wow that's a lot of dead crayfish!" "Softshells" are outstanding bait for everything that swims too.

 

More often than not in the summer, no matter where I am, I encounter at least one or two dead fish... ??? that's hardly unusual.

 

I would say, without anything more to go on than what you've said, that it's molting time for the crayfish and you just had one of those poor days on the water. It happens to everyone.

 

One slow day on the river doesn't equal an ecological catastrophe.

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You bring up a good point, JS. Adventurer568 ... did you actually pick up any of those "dead" crayfish? Did you look closely enough to see if they are actually dead critters or just shucked skins from a molt?

 

Not as silly a question as it seems.

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Back in the day you would sometimes see that when they changed the generation flow regime. The Housy used to have a generating station up in Mass. and when they released the river would rise during the morning then fall over the course of the rest of the day. Depending on the time of year you could see changes in the water clarity and I would assume dissolved oxygen and other water quality parameters. I know they no longer have the same flow changes that they did back then but If it hasn't been raining recently and the summer temps are starting to climb, some mortality might be expected. Another thing is that there might be an issue in one of the tributaries that is effecting the main river below the mouth of the trib.

 

Steve

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Years ago used to get a copy of a monthly or so newsletter with a title like The Potomac River Reporter, which would list river conditions, the pollutants released into the rivers along with fish advisories. Maybe the river you were fishing has something similar; even if it's a week or month late explaining the situation for when you were on the water.

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