Scientist: Frog's decline threatens Sierra ecology

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Frogs vs. Trout? It's a red herring...

Post by avidskier » Sat May 27, 2006 2:56 am

I've been discussing this topic off and on for a couple of years with a friend that works at the Fish and Wildlife Service. There are a number of factors that don't quite seem to add up.

Trout have been nearly ubiquitous in the Sierras since before World War II. Read books from that period, such as "Waters of the Golden Trout Country" and "Yosemite and Kings Canyon Trout" (1946 & 1947 by Charles McDermand), which document both broad distribution and much healthier populations of native and non-native trout in the Sierras, yet yellow-legged frogs apparently thrived in the face of that evil onslaught until just recently. Why do researchers not explain the disconnect between the broad stocking of trout, as well as prior much higher populations of trout in the waters they inhabit, and the much later (by many decades) decline of the yellow-legged frog? It's a glaring oversight in the overly simplistic cause-and-effect theory that trout are a primary cause of the frogs' decline.

There are other holes in the "trout as cause" theory. According to one of the primary researchers on the decline of the frogs, Roland A. Knapp of the Sierra Nevada Aquatic Research Laboratory:
"The combination of data from Wallis (1952) and Botti (1977) suggests that approximately 34% of Yosemite National Park lakes still contain fish (Elliot and Loughlin 1992)."

Is it reasonable to conclude that the water-bound residents of 1/3 of an area's lakes are responsible for a species' decline across the entire area?

Let's agree for a moment with D. Knapp's theory that introduced trout are a primary cause of frog decline, and see what he says about another area receiving attention, Kings Canyon National Park:
"However, a considerable amount of inter-drainage variation in the relative proportions of fish-containing versus fishless lakes is apparent from a second survey by Bradford et al. (1994a). This survey included 104 lakes in a particularly remote portion of Kings Canyon National Park, and trout were only found in 17%."
Wouldn't we all know a lot more about frog decline if we studied what's threatening them in the 83% of that basin's lakes that don't contain trout?

I do believe that trout have some impact on frogs, where trout are found, but surely native predators such as garter snakes, birds, and coyotes are much more mobile and ubiquitous threats across the frogs' range. Some combination of environmental causes is tipping the scales and denying these predators their froggie dinners across the frogs' entire range. Focusing on trout, found in a minority of Sierra lakes (and native to many of those lakes), only sucks research dollars as well as researcher and volunteer resources away from the greater underlying issues.

So why, you might ask, would a researcher do this? In parks and wilderness areas, researchers can get grants to study and remove non-native species. The process begs for an easy scapegoat. By highlighting only the trout "issue," bioligists can continue to get paid to spend summers camping in beautiful remote areas of the Sierras, gill-netting and removing trout (which according to the numbers they provide affects somewhere in the range of only 17-46% of Sierra lakes). Nice work if you can get it. One biologist has made a tidy living from this theory for over a decade. Doesn't he have to release supporting "findings" to reinforce the valuable expenditure of last year's grant, and to set the stage to get awarded next summer's grant funds? It appears to be a treadmill that's hard to get off of, and at some point, perhaps even when a theory is first offered, a researcher's professional reputation may get caught up in justifying and furthering the theory.

With so much drama and momentum built up around that theory, now even the lack of a quick rebound of frogs in the trout-cleared lakes must be blamed on the removed trout (they damaged the ecosystem so thoroughly). Now the problem HAS to be the trout. Now more than ever.

A much more balanced view of frog threats is presented at sites such as: http://eces.org/archive/ec/ecosystems/a ... ml#sources
The problems facing amphibians are global and multi-faceted. The fungus killing yellow-legged frogs in common in soil, not some new exotic invasion, and it is a documented factor in amphibian declines and extinctions as far afield as Australia and South America.

What else could be involved? Naming global warming and UV radiation as contributing factors seems like a bit of a cop out: they're too trendy and they're a convenient shift of blame and response away from local action. Deformities in frogs may be linked to viruses. What are we going to do, vaccinate amphibians? The decline of mountain yellow-legged frogs may be linked to the use of pesticides in the Central Valley. See the work by Gary Freel (spelling?) of the USGS. Pesticide use issues would require entering the arena of the EPA registration process - a real "can of worms" especially under the present administration. If you were successful providing information justifying the need to ban or more closely control some chemical applications, you would be assailed on the economics. What would be the effect on agricultural output? On jobs?

Unfortunately too few Sierra lakes have trout to have their removal make much of a difference either way to the frogs. Through the siphoning off of valuable research dollars some underlying decline factors may go relatively unexplored and unaddressed. We may see another decade of trout-targeting papers (how the trout destroyed lakes long term, even when they're no longer in habiting those waters) before that horse is thoroughly beaten to death.

My bet is on mercury. Rain arrives on California's shores with 300% the estimated pre-industrial level of mercury, and due to interaction with ozone once it starts inland contains 44% more mercury when it falls inland. Methylmercury is toxic to tadpoles at concentrations of .05ppm (Chang, et al 1973), can build up in vertebrates to concentrations many thousands of times greater than mercury levels in the surrounding water, and can be a greater problem in clear bodies of water with low dissolved organic matter (Gorski 2006).

Effects of methylmercury chloride on Rana pipiens tadpoles
http://www.sciencedirect.com/science?_o ... 55f3157c63

Mercury From China Rains Down on California
http://www.evesgarden.org/archives/2002 ... California

Study shows link between clear lakes and contaminated fish
http://www.engr.wisc.edu/news/headlines/2006/Feb15.html

Up to 83% of the mercury load to the Great Lakes comes from atmospheric deposition (see Shannon and Voldner, 1995).
http://www.epa.gov/owow/oceans/airdep/air2.html








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more ribbetting

Post by gdurkee » Sat May 27, 2006 11:07 am

Hmmm. Not sure where to start here. I'll start by agreeing with you. Yes, there are definitely other factors affecting froggie decline. Two things seem to be going on. At a macro scale, frogs are being eaten by fish. Period. Specific lakes that have fish don't have frogs. Find me a lake that has fish AND a substantial frog population (over, say, 50 adult mountain yellow-legged frogs). You can't do it. You can, though, find lakes with healthy frog populations (200 to over a thousand) and no fish. Kind of a clue to what's going on.

It's important to distinguish the individual lakes, not just a blanket: "83% of lakes in XXX." How many of those lakes are actually suitable frog habitat? It's not a hugely meaningful statistic. More importantly, you're wrong that the frog populations don't rebound when the fish are removed. In every case that I have personally witnessed in Sequoia Kings (about a dozen lakes now) the frogs are back immediately (like in weeks) and in very large numbers where they didn't exist before. In hiking for 35 years in Yosemite and Sequoia Kings, I have never seen significant populations of frogs occur where there are fish. Maybe one or two frogs, but not dozens or hundreds as occurs immediately upon fish removal.

But, you touch on an issue that the researchers are definitely interested in and absolutely not ignoring, as you imply: Why is this happening in the last 30 years? You're absolutely right that fish have been around since the late 1800s when they were introduced in alpine lakes -- which had NO fish before then (and I'm only talking about elevations above about 9,000 feet where there were almost no lakes between Northern Yosemite and southern Sequoia that had fish before they were introduced -- I'm less sure of distribution outside those areas).

Next, and here you're very likely right, is the micro scale. Something else is for sure happening. Frogs are clearly dying for other reasons. In those frog populations that have mass die-offs, Chytrid is usually present in all of the frogs. You're right that it is present world-wide, but it has only shown up in the last 10 (??) years in Sierra frogs. It's also not at all clear that it even existed in the US much before then. It is likely a new pathogen to our populations of frogs.

The biologists are now looking at what makes them susceptible to this fungus. My money, too, is on airborn pollutants. The worst Chytrid outbreaks have been in areas of Sequoia Kings that have the worst (to my eye, but also actual pollution data) visible pollution -- the Kern Canyon and along the west slope of Sequoia Park (Tablelands, Pear etc.).

Also, it appears (and I'm on shaky ground here) that the frogs that succumb to Chytrid are already weakened prior to visible infection -- they show very low fat content. Also being looked at is skin secretions that fight infection. Something may be happening at the molecular level that compromises this system in the mountain yellow-legged.

I think part of the problem is that you and others seem to be focused on one cause. At the moment, the one thing that can actually be done to at least preserve the frogs in small areas is to take out the fish in a drainage that the fish can't get back to. That at least preserves the frog populations for those areas and preserves a reservoir for them to recolonize other areas. This is critical to their survival. I think the accelerating decline has been because when one population is wiped out by Chytrid (or other pathogens that have been documented), there are no longer nearby populations to recolonize as would have been true in the past. It is almost certainly the trout that have started that vicious cycle.

I tried that link with the "balanced" presentation. It seems to be blank. Also, I'm more than a little confused by you saying that "Doesn't he have to release supporting "findings" to reinforce the valuable expenditure of last year's grant, and to set the stage to get awarded next summer's grant funds? It appears to be a treadmill that's hard to get off of, and at some point, perhaps even when a theory is first offered, a researcher's professional reputation may get caught up in justifying and furthering the theory."

These guys publish in peer-review journals. Sure, they could probably get away with shoddy data for awhile. But all of the data by a number of different researchers is showing the same things. The predictions they make are being borne out by field experiments. It's all agreeing internally. That's what science is all about. Taking a swipe at them because "biologists can continue to get paid to spend summers camping in beautiful remote areas of the Sierras, gill-netting and removing trout" is specious black-helicopter nonsense. The initial work on frogs & fish has led directly to current research on Chytrid and airborne pollutants -- they are not ignoring, covering up or tweaking the data so they can spend time in the backcountry floating in alpine lakes. They are following the data.

Many of these researchers have generously submitted articles to Sierra Nature Notes. Check out the Archives section at http://www.yosemite.org/naturenotes.

I remain, respectfully,

George, Defender of Frogs

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PS

Post by gdurkee » Sat May 27, 2006 11:10 am

PS: AvidSkier. I'm not sure, but I think your long link (Effects of methylmercury chloride on Rana pipiens tadpoles) needs to be broken in half -- or even thirds. It may have caused the margins to widen beyond what they usually are. Maybe you could edit it and see if that helps to keep the lines wrapping in a reasonable width.

Eric, does that seem like what's happening?

Thanks,

George

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Post by giantbrookie » Sat May 27, 2006 11:22 am

Avidskier, you bring up some good points and have clearly spent some time researching this. Knapp and fellow researchers are well aware that trout are not the sole cause for the decline of the MYLF. Unfortunately, trout are probably the easiest of the several identified factors to tweak in an effort to protect the frogs (ie it's much harder to mitigate against the fungus and the larger scale environmental factors are similarly more difficult to control at this time), so the trout have been left to take the fall. If you've seen the trout distribution versus frog distribution maps, I think it's pretty difficult to deny that trout have had a negative effect on MYLF populations. Regarding the 34% (Yosemite), it is important to think about the last part of that sentence "...suggests that approximately 34% of Yoseemite National Park lakes STILL contain fish..." (my emphasis there). The number of lakes that once held trout prior to cessation of stocking is vastly greater. Large numbers of rainbow-trout stocked lakes in northern Yosemite have gone fishless, for example (Flora, Spotted Fawn, Boundary, Inferno, etc). The same is true of Seki, where many lakes have gone fishless in the past few decades. Thus the majority of lakes deep enough to support trout (and this is sort of similar to the lakes that will support MYLF because their polliwogs need to overwinter) in the NPs probably had fish at one time, just as the vast majority of lakes in the areas surrounding the NPs do (or at least did until very recent changes in stocking policy).


Regarding the history of coexistence of trout and MYLF, I think there is no question that in many fisheries the trout did indeed wipe out the MYLF. McDermand's own accounts provide anecdotal evidence for this as there are a number of accounts of obese trout gorging themselves on polliwogs and you know what kind of poliwogs those are. At present most of the southern Sierra lakes with coexisting MYLF populations and trout have very low trout population densities (this means very nice sized trout, by the way).

I am personally aware, however, through 40 some odd years of hiking about, of examples wherein the trout's presence cannot be held responsible for the MYLF extirpation in a given lake. At Vogelsang Lake, a lake that had held trout for decades as of my visit there in 1969, I saw lots of MYLF polliwogs. In fact, given that the fish were lying low that day, I thought it meant there weren't any fish! Similarly at Mildred Lake in 1979 I saw plenty of polliwogs and the apparently abundant brookies were laying low at the time. Like Vogelsang, the fish and Mildred and frogs were apparently doing well together for a very long time, but it is likely that something else did them in .

The southwestern Seki high country has a number of lakes that certainly don't have fish today, and I suspect there is at least one remote, trailless, major basin that never held trout (potential spawning looks too good for there not to be fish it fish had ever been introduced). These lakes lack MYLF too, again pointing to another culprit for their extirpation there.

In Desolation Wilderness MYLF populations still exist in lakes that have held significant trout populations for decades; some of these lakes have or have had very high trout population densities. In fact most of the MYLF lakes in Desolation are trout-bearing lakes, in stark contrast to the pattern in the higher altitude central and southern Sierra.

Again, there is no question that trout are not the only culprit in the decline of the MYLF, but the data, at least in the central and southern Sierra that show a very good correspondence between trout bearing, MYLF absent, and trout absent MYLF bearing lakes makes a good case for trout having had a major detrimental effect. As an avid fisherman, I don't like to see the trout get scapegoated, but I don't think I can deny the strength of the data, either.
Last edited by giantbrookie on Sat May 27, 2006 12:10 pm, edited 1 time in total.
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Vogelsang

Post by gdurkee » Sat May 27, 2006 12:04 pm

Interesting memory about Vogelsang (though I also have to say I don't remember frogs there in the 70s, but that may not mean anything). It is definitely one of the mysteries. Vidette is another -- I talked to a biologist who remembered a zillion frogs there in the 50s (and, fortunately, actually documented it). Frogs now exist there in only 2 (??) lakes that don't have fish.

I think Vredenburg at one time thought a tenuous co-existence was possible where there was a safe area for the frogs -- for instance a very shallow shelf that the fish couldn't get to. This was true for many years at Bullfrog Lake, where both frogs (in small numbers) and fish occurred. I've seen no frogs there for the last 15 years (and probably a good example for this discussion since there are no nearby populations to recolonize each other. I think one by one they all died out).

I'm also wondering if the size class of the fish were a factor -- not big enough to eat large frogs. When they got larger, they would get all the adults. Probably another small factor among many.

Still, why did things really go to heck beginning in the mid-70s or so? Something I should know, but don't. I'll write Vance.

Not sure about fish introductions -- as you well know, the records are marginal to non-existent. It's hard for me to imagine that fish weren't at least dumped by coffee can into almost every lake between Yosemite & Sequoia. Maybe they just didn't take in some areas?? Also, of course, there's just an awful lot of lakes that aren't good frog habitat (too deep, no mud/sand to overwinter in; frozen over too long). I think you have a point, but not sure the absence of one or the other is good evidence for other causes. Definitely worth looking more closely at though.

(and yours a much more tolerant and nicely worded reply than mine... It's just that the black helicopter mindset just ticks me off. Sigh.)

g.

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Re: Vogelsang

Post by giantbrookie » Sat May 27, 2006 1:01 pm

gdurkee wrote:I think Vredenburg at one time thought a tenuous co-existence was possible where there was a safe area for the frogs -- for instance a very shallow shelf that the fish couldn't get to.

I'm also wondering if the size class of the fish were a factor -- not big enough to eat large frogs. When they got larger, they would get all the adults. Probably another small factor among many.

Still, why did things really go to heck beginning in the mid-70s or so? Something I should know, but don't. I'll write Vance.

Not sure about fish introductions -- as you well know, the records are marginal to non-existent. It's hard for me to imagine that fish weren't at least dumped by coffee can into almost every lake between Yosemite & Sequoia. Maybe they just didn't take in some areas??

(and yours a much more tolerant and nicely worded reply than mine... It's just that the black helicopter mindset just ticks me off. Sigh.)

g.
George,

As always thanks for your interesting posts and info. I'll admit, in the very early days when the MYLF was just emerging as a cause celebre I was fairly miltant in support of the fishing community's views. Then I was shown some of the data and I really had to change my tune. I think it is also true that in the early days, the MYLF supporters took some equally absurd stances in decrying the unnaturalness of trout stocking. For example, I can remember statements made in the press about how severely the trout "bombing" runs affected the wilderness serenity. I've fished over 600 lakes spanning 40 years and witnessed only one "bombing run" and I'd wager the folks making those statements never had (in the meantime I had experienced numerous private plane flyovers, numerous helicopter flyovers, hordes of grazing cattle, etc., etc.). Moreover there were alarmist statements by various folks, including those with the USFS of an across the board cessation of fingerling air drops and possible extermination of a large number of self sustaining fisheries. Statements such as the above led the angler community to believe that they were being unfairly scapegoated for environmental degradation of the wilderness when it was obvious that there were so many other human intrusions diminishing the wilderness experience.

It goes without saying that MYLF advocates and the angler community got off on the wrong foot, but we've come along ways since then and I will continue to do my best to help my fellow anglers understand what is going on and why. I really hope to see a more cooperative relationship between the angling community and environmental advocates, similar to what they have up in Washington state (again, it's really instructive to see what they're doing up there, even if their specific issues don't include the MYLF). Things are way more adversarial here than they should be.

Getting to some of your points above, it is very interesting to think about some of these factors. In terms of coexistence, I agree that there is something about certain lakes that gives the frogs or tadpoles an advantage they don't seem to have in the average trout-bearing lake. In one lake I am aware of that has a low density of enormous rainbows, I think the MYLF tadpoles may be able to do OK because there are lots of talus piles in the lakes and the tadpoles can hide in the crevices (plus, there just aren't that many prowling trout). One baffling lake is Woods Lake. I'm curious to know what you think or have heard about that one. The lake has an absolutely astounding number of brookies in it, but there are still frogs (at least there were as of 1997 when I was last there). Roland told me he thought the polliwogs were able to overwinter in the some fishless ponds nearby, then the frogs migrated as adults into Woods. On the other hand, most of the lakelets around Woods also have super high density populations of brookies.

Regarding the fish introductions, I too always believed that every lake with any potential for floating trout had been stocked in some form or fashion at some time in its history, until I chanced upon this one area, which is rather vast: all of the tributary Kern-Kaweah river drainages, excluding the trunk stream (has fish up to lake 11040+), and everything on Red Spur. According to McDermand's writings, these drainages were still fishless as of whenever he wrote a chapter for a book "High Sierra Wonderland" that was published in 1960 (provides sort of an update of his 1940's observations chronicled in his two famous books). McDermand speculated that DFG may have been thinking about air dropping those at the time of his writing... That group of drainages is so exceptionally remote (way off trail by and separated from trails by difficult off trail travel) it would have been pretty difficult to stock by any other means other than air drop. The lakes in the drainage span a huge variation in ecological setting, etc. Many of them appear to have all the ingredients of places that should support frogs, as well as the fact that the streams and lakes appear to have all the ingredients to sustain trout populations as well. I would be very interested to find out whether fish were ever introduced there. I am aware of the fact that the planes apparently made it down the west flank of the Kern to the next mini drainage north of the Kern-Kaweah.

In any case you are certainly right in stating that the absence of fish and frogs doesn't say that the absence of frogs is due to some cause other than the fish. This correspondence is merely suggestive that there is in fact another cause, whatever it may be. The one I've heard mentioned as a possible culprit for that particular area is that dread fungus.
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Post by ERIC » Sat May 27, 2006 4:57 pm

George,

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Re: Vogelsang

Post by caddis » Sun May 28, 2006 7:50 am

gdurkee wrote:It's just that the black helicopter mindset just ticks me off.

g.
Image The real culprits for the radical decline in MYL frog populations are the Environmentalists Image

They brought the pathogens back from South America and infected every watershed in the High Sierra when they pranced around examining amphibians


Yes....the frogs were loved to death


That's my theory (absent helicoptors) take it or leave it Image
Image

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Gotta kiss a lot of frogs...

Post by gdurkee » Sun May 28, 2006 10:06 am

The real culprits for the radical decline in MYL frog populations are the Environmentalists
It's even worse than that. All those lonely researchers looking for their prince -- it's herpes.

Ribbet

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Post by AldeFarte » Sun May 28, 2006 1:08 pm

I am no expert, just some guy trying to figure it out. Lets see. The frogs come back in big numbers when the trout are eliminated from systems in which they have co-existed for many decades. [Paraphrasing George]. They have disappeared from systems that have no trout. There is an apparently introduced fungus that does a better job of eliminating them than trout. These are just a few of the inconsistancies in this discusion.Somehow in my feeble brain, this does not add up to trout being the primary culprit in the decline of our beloved. One thing is for sure, the virosmental cannot be trusted to make an informed decision. And sorry to say ,but many researchers and biologists have made a consious decision to be in that category. "I can back those statements up many times over on a more appropriate forum." So,I think there should be an immediate cessation of the ill advised and senseless persecution and gill netting of high mountain trout! :) jls

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