Snail Die Off in Lake Davis

[1flyfisher]

I sent off this letter to CADFG to see if we can get an answer to why the snails have died off in lake davis. Hopefully they are attempting to find an answer and solution. I will post their response when I receive it.


July 21, 2010

Amber S. Rossi
District Fisheries Biologist: Plumas/Sierra County
California Department of Fish and Game
P.O. Box 419
Quincy, CA 95971
Phone (530) 283-6864


Dear Amber Rossi,

I am writing to you as one of many concerned Lake Davis fly-fishermen regarding what appears to be the complete die off of the entire snail population in Lake Davis. Myself and others have noticed a steady yearly decline over the last 10+ or so years following the first rotenone treatment in 1997. Each year fewer and fewer snails could be found. Now they are nowhere to be found anywhere in the lake. Historically snails could easily be found floating in the water column from spring through the summer into fall any day of the fishing season. The population of snails was always quite massive as they are extremely prolific breeders. The snails provided an extremely important food source for the trout population especially in the fall prior to winter ice over when floating snails were eagerly eaten by hungry trout fattening themselves for winter survival. Aside from being a major food source for trout they also perform a variety of important functions such as cleaning the lake of dying plant and animal matter which in turn dramatically improves water quality.

Now they are nowhere to be found. Not a single one. I have looked all over the entire lake this year over a course of 18 days of fishing and have not been able to find a single snail of any type. If they are present they are not difficult to find as they regularly float to the surface and can be found in the water column, washed up along the many shallow points, clinging to weed beds, or floating on the surface all over the entire lake. Over the past many decades of flyfishing Lake Davis I would always see hundreds every day. I have spoken to dozens of other fly-fishermen this season and no one has been able to find or collect a single one. Last season there was a small remaining population in a cove across from Mosquito Slough. That last remaining population of snails are also now gone.

Snails have always existed in the area creeks and in Lake Davis and they are an extremely vital part of the fishery and now part of that environment is dying off if it hasn't entirely already died off. Snails dying off and the trout covered with various parasites seems to indicate a very serious problem with the lakes water quality.

Are any studies being conducted to determine why they are dying/died off?
I would like to know exactly what cadfg has been doing to determine why this important trout food source has died off?
I would also like to know what cadfg is doing to reestablish the snail population?

Sincerely,


A Concerned Lake Davis Fly Fisherman

[michaeln]

I doubt if they have a snail form letter all ready to respond with. Guess they'll have to slap one together!

[1flyfisher]

I emailed it actually.

[1flyfisher]

We'll see what happens. This should be interesting. Hopefully they have an answer that includes the snails will be restored to prior years populations by next season. Anything else will suck. I can't deal with the snails disappearing. Parasites are bad enough.

[OceanSunfish]

We'll see what happens. This should be interesting. Hopefully they have an answer that includes the snails will be restored to prior years populations by next season. Anything else will suck. I can't deal with the snails disappearing. Parasites are bad enough.

Just an outside guess, but I have to think that the inability to refill that lake to FULL at least once after the treatment has not helped with regards to snail population as well as the parasite issue.

The lake filled immediately after the first treatment (of course it wasn't drained much to begin with...) and all "foods" rebounded nicely. Some of those back bays had snails floating on by all the time in 1999 to 2001. Then, of course.... Ugh.

[1flyfisher]

Sorry but I am a bit confused by what you are saying.
There were few snails around well before the second rotenone in 07 if that's the low water levels you are talking about with your first sentence. The snail population was in decline quite a few years before the lake was treated a second time in 07. The lake was treated in 97. After 97 lake levels were high and there were still snails around for a few years after. But they were in a slow decline from year to year following the 97 treatment well before low water years of 06-09. There haven't been many snails around for some 7-8+ years now, each year fewer and fewer and now there are none to be found Snails breed quite rapidly and water levels in and of themselves going down or up have little effect on their reproduction. A handful of snails can result in massive amounts quickly. To me at least it seems to point to the 97 rotenone treatment had a slow poisoning effect on the snails. The 06-09 low water level quite likely played a role with the parasites.

Maybe this timeline will clear up things.
1980-1997 Plenty of snails
1997 Lake levels are lowered Lake is Rotenoned
1998-2005 Snails still were around with normal populations but declined steadily year by year after rotenone. Lake levels increase and many high water years with lake full.
2006-2007 Lake level is lowered beginning in 05/06 and lake is rotenone a second time in 07.
2006-2009 lake has a period of low water levels but snails decline was evident years before the low water in this period.
2010 Lake has filled up No snails to be found anywhere.

Just an outside guess, but I have to think that the inability to refill that lake to FULL at least once after the treatment has not helped with regards to snail population as well as the parasite issue.

The lake filled immediately after the first treatment (of course it wasn't drained much to begin with...) and all "foods" rebounded nicely. Some of those back bays had snails floating on by all the time in 1999 to 2001. Then, of course.... Ugh.

[OceanSunfish]

I guess what I meant to say is that it wouldn't hurt to have the lake full again and again and again..... then the "handful" of snails could regenerate the population. To me, a full lake level year after year could only help mitigate all the side effects from rotenone, etc. Also, a lake consistently allowed to fill every spring would provide a constant by which theories could then be more easily measured.

Right now, you, I , and everyone else are just chasing our tails trying to figure out what happened at that lake! Sad.

[1flyfisher]

Snails in davis

I guess what I meant to say is that it wouldn't hurt to have the lake full again and again and again..... then the "handful" of snails could regenerate the population. To me, a full lake level year after year could only help mitigate all the side effects from rotenone, etc. Also, a lake consistently allowed to fill every spring would provide a constant by which theories could then be more easily measured.

Ok now I understand your point. I agree as I feel there is an environmental issue causing the snail population to die which has to do with water quality likely related to the rotenone so more and better higher water couldn't hurt. I think we are looking good. The lake filled up nicely since last year and an average snow pack will likely have the lake full or very close. There isn't too much more to go. If there are a handful of snails remaining somewhere in the lake they could reestablish themselves quickly as snails breed like crazy. Hopefully there are some that are going to survive. Right now there are none to be found anywhere. But if a few remain somewhere then they can come back. All it takes are a few.

Right now, you, I , and everyone else are just chasing our tails trying to figure out what happened at that lake! Sad.

Rotenone happened at the lake. When you do something like rotenone-ing a lake it throws the whole system out of balance. It is very damaging, but I was for it as the pike had to go. When Frenchman's was treated with rotenone it wrecked havoc on the blood midges. It took years for them to come back but eventually they did come back. Insect can fly and spread from one lake to another. Davis to Frenchman's for instance. Snails can't fly though so if they die off entirely that will be it. Unless cadfg choose to reestablish them which would be easy and simple for them to do. I wrote a letter to cadfg so we shall at least get to hear what they have to say regarding the problem and perhaps a more professional scientific theory or answer.

I failed to mention the catfish in the other thread. Pete mentioned the crawdads. The lake was over run with catfish prior to the rotenone in 07. I was one of the few still fishing the lake in 06/07 and that last summer there were so many catfish it was unbelievable. I would paddle over the points and several dozen would scatter. You could see several hundreds in a day. The cadfg said the remaining fish population was like 85% bullheads. The way they were all over the shallow points it looked to me like they were mopping up the snails. That was my original guess in 06/07 that the catfish were feasting on them. But catfish or crawdads can't wipe out snails by themselves. They could put a major dent into the population but not drive them down to levels that they currently exist at (which is none to be found....so far). As jon said it may be a combination of factors. That could very well be the case. Rotenone, catfish and crawdads, water rapidly lowered in 2001 for ramps, poor water quality from low water levels, tons of cow crap washing into the lake etc.
Well we shall see what the cadfg biologist has to say. Hopefully they can shed some light on the snails disappearance.

[1flyfisher]

A letter about snails sent via snail mail.

I doubt if they have a snail form letter all ready to respond with. Guess they'll have to slap one together!

[FRSam]

Nice work Paul. I forgot about all those bullheads and like you say there were hundreds if not thousands of them off all the shallow points and talk about a vacuum cleaner....

If you don't mind I'd like to copy and paste your letter to Rossi, add a little note, and email it to him.

I'll bet the response will be something along the lines of snails are cyclical in their life cycles where they peak, disappear and then peak again...adding of course we've seen this in other Sierra lakes and it's got nothing to do with anything we've done....

We'll see....

Pete