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. :D


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

[1flyfisher]

Go ahead and copy it, who were you going to send it to?





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

[FRSam]

I thought I'd send it on over to Amber Rossi as well...let them know there's more than one that has these same feelings. (Make that wheel SQUEAK!!!)

Pete

[1flyfisher]

Go for it.....she hasn't responded to my letter yet.......I am dying to hear their answer for a variety of reasons.


I thought I'd send it on over to Amber Rossi as well...let them know there's more than one that has these same feelings. (Make that wheel SQUEAK!!!)

Pete

[michaeln]

Go for it.....she hasn't responded to my letter yet.......I am dying to hear their answer for a variety of reasons.

Any response from them yet?

[1flyfisher]

Nope not a word. I figured I would have gotten something in the form of an email response but it hasn't happened.



Any response from them yet?

[michaeln]

I figure the only reason I got a response from them about the copepods was that they already had one made up that they had previously used. They probably don't have a pre-made answer for the snail thing.

I'll be surprised if they answer you at all.

[Chris Evison]

The last time I was on Davis ( July 4th) I saw snails floating on the surface in the camp five area in the morning. Just saying I have seen some snails, so they aren't all gone..............

[Troutstalker55B]

Chris,

That's great news, but do you remember when there was millions of them in the shallows? Those numbers of snails made that lake famous for large trout and we need those numbers back. Thanks for letting us know, it is somewhat uplifting......

Jon.

[1flyfisher]

At least someone has seen a few. They are about 99.9% gone at the moment. But It only takes a few snails to survive to repopulate the lake. That is if the few remaining can survive what ever is killing them. It may take several years till we see snails as was usual on Davis but I can live with that, so long as they can come back eventually.
Snails at Camp 5/south end is a good spot for them to be scattered/blown throughout the rest of the lake.


The last time I was on Davis ( July 4th) I saw snails floating on the surface in the camp five area in the morning. Just saying I have seen some snails, so they aren't all gone..............

[1flyfisher]

Millions, They were everywhere. If whatever is causing them to die off reverses or goes away (rotenone?) and a few can survive whatever is causing it then they have a shot at coming back. I still haven't heard anything from cadfg on it. I guess they are fed up and don't want to look into it and figure out what is causing the die off. I will wait a little longer on receiving an email then I will call them and see if they are looking into it.


Chris,

That's great news, but do you remember when there was millions of them in the shallows? Those numbers of snails made that lake famous for large trout and we need those numbers back. Thanks for letting us know, it is somewhat uplifting......

Jon.

[Tracy Chimenti]

I hope they recover. They eat alto of them in the fall and winter.

let's just hope they don't bunch of slimy, brood-stock snails.

[1flyfisher]

Well I have not received a response from CADFG regarding the letter I sent to them inquiring as to why the snails have died off in davis lake so I called today. Of course I never got through and was only able to get to Amber Rossi's voice mail. So, I left a message for her to either call me back or email me back,,,,I am still waiting to hear back and see if they have looked into it and if they have any answers.

[michaeln]

Thanks for the update. I'm not surprised they have not responded though.

[1flyfisher]

Neither am I.



Thanks for the update. I'm not surprised they have not responded though.

[ycflyfisher]

1,

I'm actually quite shocked you haven't gotten a response to this one. I've never posed a question to a DFG staffer that didn't get a response in a reasonable amount of time. Even if the response was time consuming to craft or if the staffer in question was not able to either answer my question or thought my concern was "off base". I've always gotten a response of some kind. Your original message is definitely one deserving of some kind of response IMO. I'd suggest contacting another staffer in the same office in the event that Amber may be out for a prolonged period of time and simply forgot or didn't have the chance to update her email autoresponse or voicemail.

[1flyfisher]

I emailed her on July 21 and I called yesterday Aug17 and re-sent the original email again yesterday to the email address listed. So I will give them a week or so then I may try calling the local dfg office in portola if I can find another contact there. The ph # I have is just to A Rossi's vm. so I will have to find another ph number. If anyone knows the office ph# or another contact there or another email I can send my letter to please post it. I'd like to speak to someone that is involved with Davis and not a sac office person.


1,

I'm actually quite shocked you haven't gotten a response to this one. I've never posed a question to a DFG staffer that didn't get a response in a reasonable amount of time. Even if the response was time consuming to craft or if the staffer in question was not able to either answer my question or thought my concern was "off base". I've always gotten a response of some kind. Your original message is definitely one deserving of some kind of response IMO. I'd suggest contacting another staffer in the same office in the event that Amber may be out for a prolonged period of time and simply forgot or didn't have the chance to update her email autoresponse or voicemail.

[1flyfisher]

On Thursday, August 26th, 2010 my co-worker and I sampled three
separate portions of Lake Davis via D-ring dip net and boat
electrofishing. The dip net samples and the rainbow trout stomach
contents verified that there are four families of snail (Lymnaeidae,
Planorbidae, Physidae, and Valvatidae) currently residing in the lake.
More than likely, the snail populations are fluctuating as the lake get
back into its normal cycles. I was able to find a paper which
demonstrated the results of the first chemical treatment of Lake Davis
in 1997. I have attached a link to the paper in this email. Basically,
the paper shows a decline in snail population immediately after the 1997
lake treatment, followed by a rise in snail population as the years
progressed post treatment.

http://www.dfg.ca.gov/lakedavis/docs/1997AquaticInvertRpt.pdf

[1flyfisher]

As for the fish parasites, we are aware of the situation at Lake Davis.
We examined a number of trout from Lake Davis last year to confirm the
identity the organisms being seen. We found light to heavy numbers of
copepods on the fish. The majority of the fish lice we observed were of
the genus Salmincola. There may be a few of the genus Lernaea as well.
Common names for these copepods are “anchor worm, fish maggot” etc.
The organisms found on these particular fish are commonly found in
waters throughout the western United States. This organism usually does
not affect fish health, though its appearance on fish can be
unattractive.
The presence of this organism on fish does not render the fish unfit
for human consumption. It is not an internal parasite, but rather
infects the gills, fins and flanks of susceptible species of fish. There
are no practical treatment options available for lakes and reservoirs.

The increased numbers of these organisms being seen this year is most
likely due to the warming of the water and the high number of fish
planted into Lake Davis. The organisms were already in Lake Davis.
When Fish and Game planted the large number of trout into the lake we
provided a large number of hosts for the parasite to live on and
multiply from. The copepod numbers will decline with cooling water
temperatures and decreasing fish numbers.

Please feel free to contact me if you have any other questions.

Sincerely,

Amber


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
Cell (530) 520-4753
Fax (530) 283-2938
arossi@dfg.ca.gov

[michaeln]

The copepod letter is the same one they sent me and also to a guy on another board. It's a form letter, whether it be on paper or email. They aren't looking into it and are hoping it will go away.

[Darian]

I'm curious about why we should expect a personalized response to a number of inquiries about the same subject :?: :confused:

Seems to me that the info in the note addresses the questions that have been raised by posters on this BB. Snails are still in the lake but maybe in a down cycle and Copepods were already in the lake and will probably die off during periods of cold water.... Since there doesn't seem to be anything else look in too, they probably won't spend much time on it. But, I'm sure they don't hope that "....it...." will just go away. :-|

IMHO, the DFG response seems adequate for the questions asked whether in a form letter or not. If their response doesn't satisfy, ask a new question(s).... :D

[OceanSunfish]

Immediately after the treatment in 1997, the lake was planted heavily...... I bet more fish were put into the lake post 1997 then post 2007. HOWEVER, post 1997, the lake was allowed to fill to capacity and if it wasn't, was sure close as many of the back bays were full of water right on into early November...... BTW, it's really pretty when the water is right up high on the shoreline with the trees in the background in Freemans, Fugawe, etc. And, you can actually launch at Lightening Tree!

Anyway, I surmise the number of fish planted per acre foot of water was probably less in 1997 even tho more fish were put in post 1997 vs. post 2007 when the pool was much smaller to assist in the treatment. And, there were a '****-load' of fish planted post 1997!

I think the explanation from DFG is pretty adequate and sensible. I've always said that if the 'powers that be' allow the lake to fill and stay filled for a few annual cycles, balance maybe restored quickly. If not, we've got an overcrowded "jail" situation without "AC" and "soap/water"..... Not a pretty picture.

[1flyfisher]

I am happy she took her time and went and took a look for some snails and found some. If they are still there they cancome back in time. It may be a while but that's the way it is. Better late than never.

Nothing can be done about the parasites cadfg can only plant new fish and hope the old infected ones stop spreading it and that they die off and decline in number. I have to believe they will decline to past numbers at some point. Who knows when but sooner or later they will fade away. I HOPE.:confused:
They will die off with higher colder water perhaps or when the fish that are infected die off and new fish cycle takes over and replaces older fish..

When you rotenone a lake it completely disrupts the balance of the lake. It will take some time before things return to normal and a stable environment. Maybe a few years from now the snails will return.


She looked into the snails and has stated the dfg's position on the parasites.
Works for me. I will send her a thankyou letter and ask why the snails declined significantly from 2003-2007.






I'm curious about why we should expect a personalized response to a number of inquiries about the same subject :?: :confused:

Seems to me that the info in the note addresses the questions that have been raised by posters on this BB. Snails are still in the lake but maybe in a down cycle and Copepods were already in the lake and will probably die off during periods of cold water.... Since there doesn't seem to be anything else look in too, they probably won't spend much time on it. But, I'm sure they don't hope that "....it...." will just go away. :-|

IMHO, the DFG response seems adequate for the questions asked whether in a form letter or not. If their response doesn't satisfy, ask a new question(s).... :D

[Jgoding]

I wonder if the older fish might have been more resistant to parasites or something as well. Not much you can do as when you see the anchor worms they're pretty much releasing gametes at that stage. I always make the point of removing them before releasing a fish as well.

[Darian]

Good point about potential natural resistance, Jeff. One of the points that DFG made was that these copepods were already in the lake and that restocking with large numbers of Trout just increased the number of hosts (Trout) for them. So, stocking has the unintended consequence of contributing to that increase. :neutral:

Might be a good time to reduce the population of Trout up there by catching and keeping a few (according to DFG, the copepods aren't a danger to humans). :-k

[1flyfisher]

I got a call from Amber Rossi from CADFG yesterday regarding the snail die off in Davis lake.
Basically she said that At this point there is no clear cut answer as to why the snails have vanished and/or gone into such a massive population decline.

She has answered my questions. If anyone has some particular question or concern regarding lake davis I suggest you direct them to amber rossi.

I am going to fish the lake in the near future for a day or two just to see if there are any half way decent size fish around. I will report back what I see and catch.

[OceanSunfish]

I really appreciate your efforts to keep us informed of the goings-on at Lake Davis. It's a special ecoysystem that, when healthy, develops big trout fast and provides a beautiful backdrop to a day's fishing.... There are an awful lot of trout fisherman and towns across this country that would just love to have a "Lake Davis" near to them.... Shame on us if we ever take this lake for granted or allow it to be yet another marginalized fishery by politicians, water grabbers, et. al.

Continue to care about the lake and keep inquiring with DFG. Politicians and water grabbers just love it when nobody cares about a body of water, fish, or ecosystem....

[gene goss]

I got a call from Amber Rossi from CADFG yesterday regarding the snail die off in Davis lake.
Basically she said that At this point there is no clear cut answer as to why the snails have vanished and/or gone into such a massive population decline.

She has answered my questions. If anyone has some particular question or concern regarding lake davis I suggest you direct them to amber rossi.

I am going to fish the lake in the near future for a day or two just to see if there are any half way decent size fish around. I will report back what I see and catch.

THANKS for taking the time to follow this through.....i'll be up there next week enjoying what we do have....c u on the water.