Scientist: Frog's decline threatens Sierra ecology

[gdurkee]

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.

[giantbrookie]

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.

[ERIC]

George,

Yes, that's why you have to scroll left to right on this thread. Oversized photos have the same affect on a thread.

[caddis]

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

g.

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

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

[gdurkee]

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

[AldeFarte]

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

[gdurkee]

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].

Yes. Though I don't think "co-existed" is really the word. It might be more accurate to say that the frogs were able to survive -- either because they had habitat that the fish couldn't get to; or they reproduced in numbers that exceeded the mortality caused by the fish; or a fish lake "recruited" from other areas with high reproduction. Then something happened within the last 30 years where mortality exceeded reproduction.

They have disappeared from systems that have no trout.

No - mostly. Apparently in a very few cases. Not the rule, though. Although Giantbrookie knows of some exceptions, the majority of data collected by Vredenburg & Knapp doesn't show that.

There is an apparently introduced fungus that does a better job of eliminating them than trout.

No. As above, they were first likely "eliminated" by trout (in the Sierra populations). The decline started before Chytrid or other known pathogens caused serious mortality. Froggie Folk have gone through all (many??) of their museum specimens and have found no evidence of Chytrid in the Sierra before about 10 years ago. The Chytrid seems to be attacking already weakened populations (weakened for reasons not yet clear). Where there are no nearby populations to recolonize, they disappear from an entire basin.


As another side note, one theory is that Chytrid was introduced from South African frogs formerly used in pregnancy testing then released by some labs into US habitat.

It is not impossible that biologists have been the source of contamination and spread. They're being a lot more careful now. It's more likely that birds or something are spreading the fungus.

g.

[ERIC]

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

g.

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

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

All you have to do is ask if you want smilies that we don't have... The ones you posted are loaded and ready for future use!
Snowy and I both have the ability to add new smilies.

[gdurkee]

OK campers. I wrote Vance Vredenburg and asked if he'd summarize the latest science on frog decline. Vance did his PhD on the Sierra mountain-yellow legged frog decline. He's been working with the 60 Lakes Basin population for over 10 years now and works closely with all the other major Sierra froggy researchers (Knapp, Rachowicz, Bradford...). He's currentlly a post-doc at UC Berkeley Museum of vertebrate zoology.

Dr. Vance sez:

So, here is the scoop in three parts. I have included references so that folks can look these things up for themselves (apologies for the in review papers, but they are just more data that support the statements made):

1. When introduced trout are placed in a lake with a mountain yellow-legged frog (mylf) population, the fish eat the frogs. No one can refute that. As you know, this has been rigorously tested with large-scale field experiments by multiple biologists (Vredenburg, 2004; Knapp, Boiano and Vredenburg, in review). Co-existence between reproducing frogs and introduced fish is extremely rare (<10 documented sites out of 14,000 sites surveyed in SN; Knapp and Matthews, 2001; Vredenburg et al., 2005; Vredenburg et al. in review) and is probably only possible when tadpoles have some refugia from trout predation. The other possibility is that those sites are population sinks supported by immigrants from a nearby fish-free frog population. The trout do not eat the eggs, instead they eat the tadpoles and metamophosed frogs (both juvenile and if the trout are large enough, the adult frogs as well). The tadpoles are the most susceptible stage because they cannot escape the water (Needham and Vestal, 1938; Mullaly and Cunningham 1956, Vredenburg, 2004; Vredenburg et al. 2005).

Overall impact of trout introductions on mylf: It is difficult to say whether trout alone lead to the major decline in mylf, but they are undeniably a major factor in declines of this frog. All indications are that in the late 1970s and early 1980s many mylf populations went extinct. This is about 20 years after industrialized fish introduction began (CDFG fish hatcheries and airplanes dropped fish into all major drainages, not just once, but many times over). The fish were dropped mostly into the larger lakes. This action eliminated the largest mylf populations. The new populations of trout then colonized any areas accessible to them, downstream and upstream until they reached natural fish barriers. The remaining mylf populations were left with smaller ponds and creeks and the geographic structure of populations became more fragmented (and isolated) that before fish introductions (Bradford et al. 1993). Some people have remarked that the delay in declines of frogs compared to fish introductions must mean that fish are not important. We don't have great information on when all of the declines occurred, but we do know that adult mylf live up to 11 years based on toe bone chonology work (Matthews,unpublished data, presented at DAPTF meeting UCBerkeley 2004). So, even if you drop fish into a big lake with a mylf population, adults should be able to survive there for a decade, and maybe longer if smaller satellite populations provide new immigrants. Basically, we would expect a delay between introductions on non-native trout and extictions of mylf.

2.Multiple factors: It is likely that multiple factors are involved in amphibian declines. From around the world there is evidence for a variety of factors that negatively affect amphibian populations in nature (new predators, disease, parasites, pollution, habitat destruction, etc.). In the Sierra Nevada we have several factors at play. We have direct evidence of negative effects on mylf from introduced trout (see above) and disease (Rachowicz et al. in press). We have indirect evidence of pollution (pesticide drift; Davidson, 2004), by indirect evidence I mean very strong correlations between amount of predicted pesticide drift and mylf extinctions. We have one study that tested the UV-B hypothesis, and it found no effect of UV-B on hatching success in mylf (Vredenburg, et al., in review)

3.What factor is responsible? This is difficult to answer, but for now we have three factors implicated in the decline, introduced trout, disease, and air pollution. Certainly any lake or stream with introduced trout could have contained mylf and no longer can support them. With 90% of the habitat in a large part of the SN now occupied by introduced trout (Knapp and Matthews, 2001), this factor must be heavily important. But, on the other hand, population models suggest that mylf should be able to survive pretty well even in small populations without disease and introduced trout (Briggs et al., 2005, and Briggs unpublished). So if fish were the only culprit, small populations should survive for a very long time. Here is where the word synergism is important. Disease, chytridiomycosis, is causing local extinction in some populations of mylf (Rachowicz et al, in press) and it could therefore be the culprit that could finish the job the introduced trout started. The air pollution could be weakening the immune systems of the frogs and thus make them more susceptible to disease, but this has not been tested yet. The earliest know frog with the agent that causes chytridiomycosis (Batrachochytrium dendrobatidis) in the Sierra Nevada is 1961 (Ouellet et al 2005) in a foothill yellow-legged frog outside of Sequoia National Park. In Yosemite the oldest know chytrid positive frog is a Yosemite toad collected in 1977 (Ouellet et al. 2005).

Future studies of museum collections may help us better understand the distribution of chytridiomycosis throughout the Sierra Nevada.

I hope this helps.
Vance


References:
Bradford, D. F., F. Tabatabai, and D. M. Graber. 1993. Isolation of remaining populations of the native frog, Rana muscosa, by introduced fishes in Sequoia and Kings Canyon National Parks, California. Conservation Biology 7:882-888.

Davidson, C. 2004. Declining downwind: Amphibian population declines in california and historical pesticide use. Ecological Applications 14:1892-1902.

Knapp, R. A., and K. R. Matthews. 2000. Non-native fish introductions and the decline of the mountain yellow-legged frog from within protected areas. Conservation Biology 14:428-438.

Mullaly, D. P., and J. D. Cunningham. 1956. Ecological realtions of Rana muscosa at high elevations in the Sierra Nevada. Herpetologica 12:189-198.

Needham, P. H., and E. H. Vestal. 1938. Notes on growth of golden trout (Salmo aguabonita) in two High Sierra Lakes. California Department of Fish and Game 24:273-279.

Ouellet, M., I. Mikaelian, B. D. Pauli, J. Rodrigue, and D. M. Green. 2005. Historical evidence of widespread chytrid infection in North American amphibian populations. Conservation Biology 19:1431-1440.

Rachowicz, L. J., R. A. Knapp, J. A. T. Morgan, M. J. Stice, V. T. Vredenburg, J. M. Parker, and C. J. Briggs. 2006. Emerging infectious disease as a proximate cause of amphibian mass mortality in Rana muscosa populations. Ecology in press.

Vredenburg, V. T. 2004. Reversing introduced species effects: Experimental removal of introduced fish leads to rapid recovery of a declining frog. Proceedings of the National Academy of Sciences of the United States of America 101:7646-7650.

Vredenburg, V. T., G. Fellers, and C. Davidson. 2005. The mountain yellow-legged frog Rana muscosa (Camp 1917). in M. Lanoo, editor. Status and conservation of U.S. Amphibians. University of California Press, Berkeley.

[krudler]

So, then, in a nutshell: frog or trout?

I vote trout.