Scientist: Frog's decline threatens Sierra ecology

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gdurkee
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Post by gdurkee » Sun May 28, 2006 2:48 pm

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.








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Re: Vogelsang

Post by ERIC » Sun May 28, 2006 10:55 pm

caddis wrote:
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
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Up to the minute information

Post by gdurkee » Fri Jun 02, 2006 12:45 pm

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.

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Post by krudler » Fri Jun 02, 2006 1:13 pm

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

I vote trout.
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Post by caddis » Fri Jun 02, 2006 3:01 pm

All indications are that in the late 1970s and early 1980s many mylf populations went extinct.
The earliest known 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).
I somehow feel this gets overlooked because the easiest culptrit is trout.
With 90% of the habitat in a large part of the SN now occupied by introduced trout
I don't deny that trout reduce MYLF numbers but is the remaining 10% enough to sustain a viable population? similar to the Bison example brought up earlier....reduced historical numbers to not threaten extinction. if this were so then almost every animal would be threatened with extinction today

Can MYLF's live in habitat that can't support fish?

Another thought....If there were no trout at all in the sierra's, would disease travel faster or do just as much damage? Or, regardless of the trout, would disease reduce the populations to present levels anyway?
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Post by AldeFarte » Fri Jun 02, 2006 5:06 pm

I also vote for trout. Thanks for the input Doc. It seemed fairly laid out. I agree with caddis. The mylf is not so extra specific on habitat needs to preclude the the existance of high country trout. jls

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Post by vaughnm » Fri Jun 02, 2006 8:12 pm

I've been fishing since I was 6 (that's quite a while), and I wouldn't want to see the distribution of trout dramatically reduced. But, I certainly get a kick when I see a mass of tadpoles, or three or four frogs around 10,000 ft. I've seen them in Upper Cathedral Lake, in some ponds at Island Pass and other places. Always a kick.

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Post by giantbrookie » Fri Jun 02, 2006 9:03 pm

George,

Thanks again for putting some science in here and thanks to Vance. As you know I am in agreement with Vance's overall conclusions that I the data overwhelmingly supports the negative impact on mylf by trout. However, some of the "exceptions" are important both for fisheries management purposes and for mylf survival. What I am interested in is Vance's statement "<10 documented sites out of 14,000 sites surveyed in SN". Perhaps I'm behind in my data (I haven't received an "update" in upwards of 5 years), but aren't there nearly 10 sites in Desolation Wilderness alone where mylf and long-introduced trout populations (ie resident for decades) coexist?

I certainly am aware of the rarity of coexistence of the two species (when the trout population has been in the lake for decades as opposed to a shorter time period). I've visited only one lake for sure in the High SN (in my definition "High" means Tower Pk and south) that had coexisting trout and mylf (confirmed by Knapp) and another that had frogs but that Knapp said had walk in population from neighboring ponds. I've also visited one lake that I'm pretty sure I saw mylf poliwogs but neither the DFG fisheries biologist covering the area nor Knapp confirmed their presence (lake has had air dropped rainbows for decades). This is out of 600 some odd lakes I've been to personally. I think the most impressive qualitative statement of the non-coexistence of mylf and fish is the age old anglers 'conventional wisdom' as to whether a lake is fishless or not. If you don't see fish or encounter a strike, you wonder if the fish are just laying low for a day. If you don't see a sign of fish life and you see poliwogs you say the lake is fishless: this has been fisherman's conventional wisdom since I was a kid (ie 40 years ago). I am still curious about the <10, though because I think something different is afoot in the N. Sierra. I've also been told that mylf carry the chytrid fungus up there but somehow don't succumb as easily. I am curious as to whether such qualitative observations are holding up with more thorough study.
Since my fishing (etc.) website is still down, you can be distracted by geology stuff at: http://www.fresnostate.edu/csm/ees/facu ... ayshi.html" onclick="window.open(this.href);return false;

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Oh, get a clue guys

Post by gdurkee » Fri Jun 02, 2006 9:54 pm

Giantbrookie:

I don't know the specifics of those exceptions either. My memory and experience seem close to his general conclusions (so far) about how they've survived occasionally with fish. The picture I'm starting to form is like the Passenger Pigeon -- once they went below a critical minimum, they crashed from predation (human & other animals). I was interested in his thought that it started close to the start if F&G air drops. I didn't know that. It makes some sense.

Chytrid is still a mystery. I think I vaguely remember someone saying that Tree Frogs were carriers but never got the disease. I could be completely wrong on that one though. Regarding the Northern Sierra, Vance and colleagues have proposed three species of the yellow-legged -- a northern, central (Yosemite to about Palisade Creek) and southern (Mather Pass to southern California) population. Possible they have different reactions to Chytrid &/or survival strategies with fish. The problem, of course, is they (the central and southern herds) didn't evolve with fish. I don't know anywhere near enough to comment on the North.

It also appears that Chytrid can wipe out a lake and, two years later, the frogs can recover. This has now happened a couple of times in Yosemite and Kings (with a reintroduction). Also from lab work.

Glad you're out there making observations and remembering. It's amazing how important that was in the early days of the frog research. There were darned few records and these guys often had to get hints of research directions from people with time in the Sierra and good memories... .

*************


For the others, I should know better, but what part of this whole and very detailed discussion are you guys missing?

Stand in front of a mirror and repeat after me:

"THE SURVIVAL OF FROGS DOES NOT DEPEND ON GETTING RID OF YOUR &*^*#!!!%%$^*& PRECIOUS FISH."

Got that?

We might not totally agree on an exact number of lakes with fish in the Sierra, but (and I'm not just talking Yosemite to Sequoia Kings, but the whole Sierra) we're talking close to 10,000 lakes & waterways --- TEN THOUSAND!!!!!! -- the majority WITH YOUR %!!##$!!^%&^* PRECIOUS TROUT.

Do you think you could maybe make room in, oh, I dunno, a hundred of those lakes for frogs? Maybe even 200 in 20 years. We're talking an attempt at a whole and healthy ecosystem here. That's what National Parks and Wilderness areas are for: both by moral duty to the planet and, not incidentally, legal responsibility to the enabling legislation of the parks and of the Wilderness Act.

These little firefights are going on all over the planet and with thousands of species, habitat and ecosystems. The attempt is to preserve some small islands (at least) of what these wild places have been for tens of thousands of years. It is, always, a rearguard action, but sometimes there's small victories and advances. It would be really nice if the people who are actually out there and, at some level, appreciating these places could show a little generosity of spirit and respect for the land.

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When I stood I thought I glimpsed my own desire. The landscape and the animals were like something found at the end of a dream. The edges of the real landscape became one with the edges of something I had dreamed. But what I had dreamed was only a pattern, some beautiful pattern of light. The continuous work of the imagination, I thought, to bring what is actual together with what is dreamed is an expression of human evolution. The conscious desire is to achieve a state, even momentarily, that like light is unbounded, nurturing, suffused with wisdom and creation, a state in which one has absorbed that very darkness which before was the perpetual sign of defeat."


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Post by AldeFarte » Sat Jun 03, 2006 12:58 am

Well George, I think "Healthy Ecosystem" is subjective. To me and the people I abuse the land with, "It is healthy now". Um ,When is a little more of a good thing too much? We have gone from a few lakes ,to a few dozen to a few hundred in twenty years. Sorry pard, But that is un acceptable to me. I think a lessoning of indescriminate air drops will cure a lot of ills in the future. If a lake can be self sustaining , then leave it alone. If it cannot keep a viable population going thru a natural spawn, then let the frog have it. Period! Only the strong survive. "Fish the foam" :)

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