California Budget Crisis and the Future of the Aerial Fish Stocking Program

For years, the California Department of Fish and Game (CDFG) has used a 1981 Beech King Air airplane to stock backcountry lakes. This aircraft has been specially modified to conduct these stocking operations and is apparently the only aircraft in the state capable of carrying out this task. The Sacramento Bee recently reported that in an effort to cut state spending, California Governor Jerry Brown has proposed reducing the vehicle fleet owned by the CDFG, and the King Air is on the list of vehicles to be auctioned off (link). The CDFG is petitioning to keep vehicles that represent special circumstances, and I'd be surprised if the King Air was not included in that petition. So, this story is still unfolding, but if the King Air is auctioned off it could end the CDFG aerial stocking program. 

This issue is of particular interest to me because I've been critical of the CDFGs aerial stocking program for some time, because of its history of poor oversight and shaky justification. For example, there are numerous examples of the wrong lakes being stocked. With today's sophisticated navigational instruments, it seems hard to imagine how this could happen. In reality, the aerial stocking program does not take advantage of these navigational advances, and still utilizes a rudimentary and error-prone method of identifying the target lakes. Mistakes can have disastrous consequences for species such as the imperiled mountain yellow-legged frog and are simply unacceptable. Second, in a paper published in 2004 we showed that of the hundreds of backcountry lakes being stocked in the central and southern Sierra Nevada, 70% actually contained self-sustaining trout populations and did not need to be stocked to provide recreational fisheries. By stocking these lakes, the CDFG was wasting scarce dollars that could have been used much more effectively elsewhere.

Fortunately, the CDFG has improved the scientific underpinnings of their aerial fish stocking program in recent years, but those changes have raised further questions. Most importantly, the CDFG has dramatically reduced the number of lakes being stocked, in part to eliminate the unnecessary stocking of lakes that contained self-sustaining trout populations and also to reduce impacts to native species. With this reduced number of stocking localities, the cost per lake of stocking has undoubtedly sky-rocketed because the underlying costs (including that of the King Air) remain unchanged. Does it really require a multi-million dollar airplane to stock a handful of backcountry lakes? Maybe the action of putting the stocking plane on the State's auction block will force the CDFG to evaluate the cost-effectiveness of their aerial stocking program. 

This could get interesting.

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The Origin of the Amphibian Chytrid Fungus

The amphibian chytrid fungus (Batrachochytrium dendrobatidis: Bd) is the cause of the most spectacular loss of vertebrate biodiversity in recorded history. To date, at least 200 species have been driven extinct and hundreds more have suffered major declines. Even amphibians within the world's best protected ecosystems have been hard-hit, including California's mountain yellow-legged frog (Rana muscosa, Rana sierrae). This amphibian pathogen appears to have emerged in just the last 50 years, subsequently spreading around the world at lightning speed. 

So, where did Bd come from and what allowed its recent emergence? These are questions that researchers have asked since its description in 1999. Using the best available methods, molecular biologists from around the world have slowly but surely been zeroing in on the answers. In 2003 and 2007, studies by Morehouse et al. and Morgan et al., respectively, used evidence that Bd had little genetic variation to suggest that Bd was a recently emerged clone, not a pathogen with a long evolutionary history with amphibians. Results published in 2009 by James et al. supported these interpretations and suggested that the emergence of Bd may have been caused by a single hybridization event.

A just-published paper by Farrer et al. now advances this story even further. Using sequences of entire Bd genomes, Farrer et al. found evidence of multiple distinct Bd strains with apparently non-overlapping distributions. However, they also found a single lineage that was globally distributed, more virulent than the geographically isolated strains, and associated with worldwide frog die-offs. Based on this evidence, they suggest that contact between two previously isolated strains produced a hypervirulent strain that subsequently spread globally, causing amphibian declines and extinctions in its wake. They further postulate that the global amphibian trade was likely responsible for bringing these genetically isolated strains into contact with each other.

Another research group is using similar methods to provide an even more detailed view of the emergence of Bd as an amphibian pathogen, and will hopefully publish their results in the near future. I suspect that we haven't yet heard the final word of this evolving story. Given the likely role of human commerce in driving the emergence of Bd, there are important lessons here for biodiversity conservation in the Anthropocene. Namely, as our increasingly global economy moves goods around the world we will inevitably also move less desirable things, including invasive animals and plants but also invisible things like pathogens. The spread of introduced pathogens from their new introduction points will often be impossible to control, and decimation of naive animal and plant populations into which they come into contact is all but guaranteed. Bd provides a sobering example of what is to come.  

The citation for the latest paper is as follows: Farrer, R. A., et al. 2011. Multiple emergences of genetically diverse amphibian-infecting chytrids include a globalized hypervirulent recombinant lineage. Proceedings of the National Academy of Sciences, USA 108:18732-18736. [link]

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Do High Elevations Provide Amphibians with a Refuge from Disease?

One of the most puzzling aspects about the impact of the amphibian chytrid fungus (Batrachochytrium dendrobatidis: Bd) on amphibian populations is the diversity of disease outcomes. In some landscapes, the arrival of Bd causes the complete extirpation of all populations, but in others it has little or no negative effect on amphibians. There are lots of reasons for these different disease outcomes, including differences between amphibian species in their susceptibility to Bd and different environmental conditions that change Bd virulence and amphibian susceptibility. The environmental condition that has received the most attention is temperature. Bd grows best at temperatures of 15-25° C and growth is greatly reduced at temperatures above and below this optimum range. Importantly, at temperatures above 30° C Bd is killed within a matter of hours, but no lethal effects are known at the low end of the temperature range (i.e., around 0° C). 

This relationship between temperature and Bd growth likely explains several general patterns related to Bd infection intensities on frogs in hot climates (e.g., tropical and subtropical regions). These include lower Bd infection intensities at low versus high elevation, low versus high latitude, and summer versus winter. However, in temperate climates little is known as to whether similar patterns hold. That is, do colder temperatures limit the growth rates of Bd and impacts to amphibians? If so, then we would expect lower Bd infection intensities at higher elevations. 

During the last several years, my colleagues and I have tested this idea using a series of studies on the Sierra Nevada yellow-legged frog (Rana sierrae) in Yosemite National Park. These studies included a park-wide (i.e., low to high elevation) survey of Bd infection intensities, detailed measurements of infection intensity over the entire ice-free period (from the cold temperatures immediately after ice-out to warm temperatures of mid-summer to cold temperatures of late-fall), and frog reintroductions in which we moved frogs from a single Bd-positive R. sierrae population to five nearby lakes that spanned a wide elevation range.

The results provided no support for the idea that the coldest habitats might provide frogs with a refuge from Bd. In the park-wide survey, Bd infection intensity was unrelated to elevation. In the seasonal study, despite temperatures that ranged from 4° C to 25° C, Bd infection intensities remained remarkably constant. And the reintroduction study indicated no changes in infection intensities related to elevation. As a consequence, in the paper that was recently published describing these results (see below) we concluded that in the temperate zone even the coldest habitats are unlikely to provide amphibians with a refuge from Bd. 

Despite this discouraging finding, we did significantly advance our understanding of Bd-frog dynamics and learned a lot about frog reintroductions as a method of reestablishing R. sierrae populations in Bd-positive landscapes. Although three of the five reintroduced populations quickly declined and never showed evidence of reproduction, the remaining two populations did produce tadpoles in the years following reintroduction and at least one of these  populations shows evidence of becoming a self-sustaining population despite ongoing Bd infections. Future reintroductions are planned to allow us to learn more about how best to conduct these reintroductions to maximize the chances of success. 

The citation for the paper described above is as follows: 

Knapp, R. A., C. J. Briggs, T. C. Smith, and J. R. Maurer. 2011. Nowhere to hide: impact of a temperature-sensitive amphibian pathogen along an elevation gradient in the temperate zone. Ecosphere 2:art93.

The paper is available here: http://vesr.ucnrs.org/pages/knapp/publications/publications.html.

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The Amazing Disappearing Frogs

This summer we focused much of our research effort on resurveying known mountain yellow-legged frog populations in Sequoia and Kings Canyon National Parks. We first surveyed these areas for amphibians and fish 11-14 years ago and found mountain yellow-legged frogs to be pretty common. Since then, on multiple occasions we've resurveyed the subset of sites that had contained mountain yellow-legged frogs during the original surveys, but no resurveys have been conducted since 2007. So this year, as soon as the snow and ice of winter were gone, we started at the southern border of Sequoia National Park and made our way north, resurveying every site at which mountain yellow-legged frogs were found during the original surveys. By summer's end, we'd covered all of the sites in Sequoia and most of those in southern Kings Canyon National Park. 

Results from this year's resurveys painted a pretty grim picture. Seventy-five percent of the revisited sites were now without any mountain yellow-legged frogs, and in some cases frogs had been extirpated from entire basins. Where frogs were still present, populations were generally much smaller than they had been 11-14 years ago. Many of these remnant populations appear to be spiraling toward extinction, and most of these will likely be gone in another five or so years. For the most part, the resurvey results were as we had expected. The amphibian chytrid fungus (Batrachochytrium dendrobatidis: "Bd") has spread through this region during the past decade, and the outcome of Bd arrival is invariably the collapse of mountain yellow-legged frog populations. What previously had been a reasonably "froggy" landscape was now one in which remaining populations were small and widely scattered. This summer, it was common to go several consecutive days and not find even a single mountain yellow-legged frog. 

But there were a few welcome surprises. In a couple of spots, mountain yellow-legged frog populations had rebounded to levels that far exceeded what we'd seen at these sites in recent years. And this had occurred despite the fact that frogs in these populations remained infected with Bd. Plans are now underway to use small numbers of frogs from these "persistent" populations to reestablish frogs at nearby sites from which they were extirpated following Bd arrival. I'm under no illusions that this will be easy, but we've got to try. The realization that mountain yellow-legged frogs are now gone from vast expanses of Sequoia and Kings Canyon National Parks, and that their disappearance is having far-reaching consequences for these ecosystems provides all the motivation I need to keep on trying.

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Another Field Season......

Well, the field season is over for another year. I've been doing amphibian-related field work in the High Sierra for almost 20 years now, and I can't remember a summer as weird as this one was. In mid-July, high elevation lakes were still frozen solid. Summer finally arrived at the beginning of August, but in early September I found myself in a backcountry snow storm. As I hiked through a blizzard of swirling white, all I could think was, "What?! Already? Summer has just started!". And for the past couple of weeks, the blue skies typical of early fall in the Sierra have instead been leaden skies portending of thunderstorms. What the heck? 

In my absence from the front country, lots has happened in the world of frog conservation. Most importantly, perhaps, was the die-off of more than 100 mountain yellow-legged frogs being housed at Fresno's Chaffee zoo. The cause of death remains a mystery. These frogs were collected in southern California as part of an effort to establish another captive breeding colony, the progeny of which could eventually be released back into the wild. This incident should serve as an important reminder of how difficult it is to maintain healthy frog populations in captivity. Whenever possible, I'd like to instead see concerted efforts to establish frog populations in suitable natural habitats across the range of the frog. Populations of the mountain yellow-legged frog have tremendous reproductive potential, and under the right conditions could produce lots of offspring for reintroduction to additional sites. And those offspring would come at a fraction of the cost of those from captive rearing facilities. The fact that fewer than 200 adult mountain yellow-legged frogs exist in southern California limits the options available, but I worry that the current focus on captive breeding has distracted us from a broader approach that includes trying to establish additional wild populations. 

The U.S. Fish and Wildlife Service (USFWS)-led effort to develop a Conservation Strategy for Sierra Nevada populations of the mountain yellow-legged frog continues apace. This effort is still in the information-gathering phase and I expect that a draft strategy won't be released until sometime in 2012, perhaps around the time that the USFWS begins the process of deciding whether these Sierra Nevada populations should be listed under the federal Endangered Species Act. In addition, the California Fish and Game Commission will soon be meeting to decide whether to list mountain yellow-legged frogs across their range under the California Endangered Species Act. And then, both Yosemite and Sequoia-Kings Canyon National Parks continue to work on their respective park-wide aquatic restoration plans, plans that will likely propose multi-decade efforts to remove nonnative trout from key frog habitats within these jurisictions. I expect that both parks will release draft plans in 2012. 

So, 2012 looks to be a busy year. Stay tuned for updates....

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Always Something New to See

One of the greatest things about my job as a field biologist is the chance to see amazing things happen in the natural world. I see fascinating stuff every day while out in the mountains, but some happenings are truly memorable. In the past, that has included seeing bears swimming in Sierran lakes, Clark's Nutcrackers eating tadpoles of the mountain yellow-legged frog, water shrews diving for food in alpine lakes, and a deer swimming in a lake to escape two coyotes intent on a late October meal. That strategy by deer of jumping into water to escape predators seems to be one that they use fairly regularly, but I've never seen other animals do the same. Until this week. 

I was in the southern Sierra Nevada doing my usual things, this time paddling around a lake to measure its maximum water depth. On this spectacular day in the mountains, I was staring at the world around me while paddling to what looked to be the deepest spot. I slowly became aware of a squeaking sound coming from somewhere in the surrounding foxtail pine forest. As the sound got louder I looked more carefully into the forest's shade. Suddenly, out of nowhere came a pika running at full speed parallel to the lake shore, with a weasel close behind. The weasel was closing fast on its prey when the pika suddenly turned toward the lake and to my amazement dove in. It then swam furiously out into the lake but the weasel stayed on shore, staring at the pika and at me. Apparently realizing that the weasel was no longer in pursuit, the pika turned to swim parallel to shore and after a minute or so of that, headed to shore in earnest. I was sure the weasel would run along the shore and grab the pika as it approached land, but instead the weasel turned and ran off into the woods. As soon as it hit the shore, the pika did the same but in the opposite direction. 

Swimming pikas?! Who knew?

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Out in the Field Again, Finally!

It has been a long winter here in the Sierra Nevada. This "spring" was one of the coldest and wettest on record, and as a consequence the higher portions of the mountains are still blanketed in snow. But now that the melt has finally begun in earnest, my field season is fast approaching. Last week I hiked into the Golden Trout Wilderness to have a look at a particularly important population of the southern mountain yellow-legged frog (Rana muscosa). This population is the furthest south R. muscosa population left in the Sierra Nevada. Populations historically occurred as far south as Breckenridge Mountain in Kern County, and included large populations in the montane and subalpine meadows along the South Fork Kern River and Golden Trout Creek. As far as we know, those are all gone now, and this population that I visited is the last hold-out in this southern portion of the historic range. 

The fact that this population is still extant is remarkable. Most of the meadows in the Golden Trout Wilderness have been badly degraded by intensive sheep and cattle grazing in the late 1800s and early 1900s that resulted in channel incision and lowered water tables. As a consequence, many of the ponds and other amphibian habitats disappeared. In addition, California golden trout (that were native to much of the South Fork Kern River watershed) were moved into the few naturally fishless lakes and streams that existed in the area, further reducing habitat for R. muscosa. And then probably sometime in the 1970s or 1980s, the amphibian chytrid fungus (Batrachochytrium dendrobatidis) swept across the region, further decimating R. muscosa populations. 

Despite all of these changes, this population of frogs somehow hung on. But for how much longer into the future they will remain is an open question. This R. muscosa population is centered on a single small breeding habitat, an abandoned stream channel filled with sedges and fed by seepage from the adjacent stream. When the stream someday moves back into this channel (as it inevitably will), the only breeding site will be gone and so too will be the frogs. As such, it is imperative that frogs from this population be used to reestablish populations in suitable habitats elsewhere in the vicinity. Based on the low success rate of developing new mountain yellow-legged frog populations, this won't be an easy task. But without such an effort, the range of R. muscosa will continue to contract until this once abundant species is all but gone from its former haunts.

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Captive Breeding Yields Another Round of Eggs

The Los Angeles Zoo is reporting that their technique of holding frogs at cold temperatures over the winter followed by a gradual warm-up in the spring  resulted in another batch of egg masses being laid in March. These egg masses subsequently hatched into hundreds of tadpoles that will be released into the wilds of southern California later this summer. For more information, check out this story. 



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New Insights Into the Cause of Recent Amphibian Declines

During the last decade, Karen Lips and colleagues have documented the spread of the amphibian chytrid fungus (Batrachochytrium dendrobatidis: "Bd") southward through Costa Rica and Panama, and its devastating impacts on amphibian populations. However, it has remained unclear whether Bd was also the cause of declines in areas north of the region studied by Lips et al., including Mexico, Guatemala, and the Monteverde region of Costa Rica. Throughout this region, a host of amphibian species either disappeared or markedly declined in the 1970s and 1980s, and the cause of these declines and extinctions has until now been largely speculative. 

In a new study published this week in the Proceedings of the National Academy of Sciences, Cheng and colleagues used museum specimens collected in Mexico and Central America during the period 1967-1987 to test for the presence or absence of Bd. Their results provide compelling evidence that since the 1970s Bd has been spreading south through southern Mexico and Central America (red dots with stars in figure). This timeline dovetails nicely with that for Costa Rica and Panama posited by Lips et al. (red dots in figure). Across their study sites, Cheng et al. also show a repeated pattern of Bd being absent from amphibians collected in the early years of their analyses followed by initial detections of Bd and the coincident decline of multiple amphibian species. 

So, it is now quite clear that Bd was a major cause of enigmatic amphibian declines that occurred in this region during past decades. The molecular technique developed by Cheng et al. to detect Bd on preserved museum specimens should open the door to a host of future Bd-related studies that take advantage of additional preserved amphibian specimens stored in museums around the world. I suspect that these specimens have many a tale to tell regarding the global spread of Bd and its impacts on amphibians. 

Further reading:
Lips, K. R. 1998. Decline of a tropical montane amphibian fauna. Conservation Biology 12:106-117.

Lips, K. R. 1999. Mass mortality and population declines of anurans at an upland site in western Panama. Conservation Biology 13:117-125.

Lips, K. R., F. Brem, R. Brenes, J. D. Reeve, R. A. Alford, J. Voyles, C. Carey, L. Livo, A. P. Pessier, and J. P. Collins. 2006. Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community. Proceedings of the National Academy of Sciences, USA 103:3165-3170.

Lips, K. R., J. R. Mendelson III, A. Munoz-Alonso, L. Canseco-Marquez, and D. G. Mulcahy. 2004. Amphibian population declines in montane southern Mexico: resurveys of historical localities. Biological Conservation 119:555-564.

Rovito, S. M., G. Parra-Olea, C. R. Vásquez-Almazán, T. J. Papenfuss, and D. B. Wake. 2009. Dramatic declines in neotropical salamander populations are an important part of the global amphibian crisis. Proceedings of the National Academy of Sciences 106 3231-3236.

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Mitigating the Effects of Chytridiomycosis - Part 2

Chytridiomycosis is the disease of amphibians caused by the fungal pathogen, Batrachochytrium dendrobatidis. Given the severe impacts of this disease on the world's amphibian biodiversity, there is a lot of interest in mitigating these impacts to the extent possible. I wrote about some of those efforts in a previous post. Doug Woodhams and colleagues have just published a paper that reviews the progress made to date in this important field (pdf). Having been involved in research that tested some mitigation strategies, I suspect that it will be quite a while before we have effective mitigation measures that can be effectively applied in the wild. 

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With Spring Come New Frog Reintroductions

On April 14, biologists from the USGS and the San Diego Zoo released another batch of Rana muscosa egg masses that were laid in captivity. This effort is part of an effort to breed this endangered species in captivity and reintroduce the progeny into the wild in southern California. For more information, check out this link. This reintroduction effort was begun last year and I'm curious to hear the results of last year's egg mass reintroductions. With any luck, there should be some second-year tadpoles swimming around out there this year. 

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Budget Battles and the Future of Ecological Research

The rhetorical and legislative battles waged in Washington, DC in recent weeks over the federal budget suggest that some major changes in science funding may be underway. It is my belief that those possible changes could have real implications for the science of ecology. For years, politicians of all persuasions have spoken of the need for federal funding of science, and this largess has resulted in major advances in many fields. However, with the ballooning federal deficit there has rightfully been increased scrutiny of federal spending on science. Clearly, we cannot keep spending borrowed money, and something has to give. In response to potential budget cuts, science advocates have attempted to highlight the value of federally-funded science in such easily understandable terms as "promoting competitiveness" and "assuring America's leading role in world affairs". Some of these arguments, while well-intentioned, marginalize entire scientific endeavors. 

For example, Representative Sherwood Boehlert (Republican - NY), who served on the House science committee and retired in 2007, argued, "One of the most important things for scientists to do is to change the vocabulary. No longer should we be talking about investing in science....because it's important for science. We should make this a national security issue. When a lot of the conversation is about the next Congress cutting or freezing all non–national security spending, we ought to take [science] funding and put it under the national security umbrella" (Science, November 2010). I understand the intent behind this statement, but what of all of the scientific endeavors that don't fit neatly under the "national security umbrella". Do scientific disciplines such as ecology no longer have a place in a world where federal budget deficits suggest to some an increased emphasis on those disciplines that have direct relevance to society? 

Maybe not, but in my view such a world would be a greatly diminished one. Numerous countries spend far more than the U.S. on the natural sciences, realizing perhaps that healthy societies and economies depend in part on healthy ecosystems. For example, the Swedish government funds the Swedish Taxonomy Initiative that aims to create a complete inventory of all multicellular species present within the country. The $10 million annual budget of this initiative isn't trivial, but the effort has already identified many species new to science, and when completed will vastly increase knowledge of Swedish biodiversity, help to identify declining species, and provide novel insights into how ecosystems function. Under Representative Boehlert's suggested focus on science as a national security issue, similar biodiversity research being conducted in the U.S. would be marginalized. 

I believe that studying biodiversity for its own sake and for the services that such biodiversity and the supporting ecosystems provide to human societies is important. But in the budgets of the future, I suspect that the value of scientific research will be increasingly viewed through a lens that discriminates between important and unimportant science on the basis of its direct and immediate relevance to society. With such a view, the only ecological research that will flourish will be that focused on important commodities (e.g., biofuel production to reduce our dependence on foreign oil) and on imminent biological threats to humanity (e.g., emerging diseases). All else will be relegated to the sidelines as unaffordable luxuries in a time of scarcity. 

But is spending money on improving our understanding of those creatures with whom we share this planet really a luxury? Or do we ignore biodiversity at our own peril? Our society will answer those questions in the coming years, and given what I suspect the outcome will be, I'm thankful that my own research can be accomplished with only a backpack, a notebook, and good pair of hiking boots.

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A Framework for Future Frog Recovery Efforts

As I’ve mentioned in previous posts, the state Endangered Species Act (ESA) listing process for the mountain yellow-legged frog is underway, with a Status Review document due to the California Fish and Game Commission this October. In addition, the U.S. Fish and Wildlife Service (USFWS) recently sent a letter to state and federal agencies stating their intention to begin the “final rule” process for listing the mountain yellow-legged frog in the Sierra Nevada under the federal ESA. Given the steep decline of both species of the mountain yellow-legged frog in the Sierra Nevada (Rana muscosa, Rana sierra), it seems likely that both the state and federal processes will end up listing both species as either threatened or endangered. These listings will accelerate the development and implementation of recovery actions across the range of the species.

To date, these recovery efforts have involved the removal of nonnative trout from critically-important lake and stream habitats, and have been undertaken primary by the California Department of Fish and Game, National Park Service, and U.S. Forest Service. These projects have set the stage for marked increases in affected mountain yellow-legged frog populations. However, they have been undertaken without much in the way of coordination between agencies. Given that these recovery projects currently affect only a tiny fraction of the Sierra Nevada, this coordination hasn’t been critical. But with an escalation of recovery efforts, close coordination between recovery projects will be essential to ensure that implementing agencies plan recovery efforts based on a mutually agreed-upon prioritization of recovery locations, and that recovery projects are uniformly based on the best available science and utilize a consistent set of site selection criteria, implementation methods, and monitoring protocols.

So, what mechanisms exist to coordinate these recovery activities? The most likely is the development of a mountain yellow-legged frog Conservation Strategy. The USFWS recently requested that all state and federal agencies with jurisdiction over mountain yellow-legged frogs and their habitat appoint a representative for inclusion on such a team, but it remains uncertain what the time frame for this Conservation Strategy will be. Ideally, the Conservation Strategy would be in place within one year, allowing coordinated recovery projects to be implemented either during the ESA listing processes or soon thereafter. This plan would identify the locations of recovery actions, prioritize these actions, and outline protocols for implementing the actions and monitoring their effects. Such a coordinated effort, with a centralized data base in which all monitoring data from recovery projects is maintained, would allow rapid assessment of the degree to which projects are meeting recovery goals.

In addition to providing a coordinating framework within which recovery projects are implemented, it is important that the Conservation Strategy be transparent to all stakeholders. This transparency will provide all interested parties with information on the criteria used to identify and prioritize recovery projects, and the locations of recovery projects. There is always a reluctance to provide the public with the exact locations of trout removal efforts due to concerns that disgruntled individuals could sabotage projects, but it is time to take this important step. It is my hope that any risks will be outweighed by the benefits that will come from fully involving the public in the task of recovering mountain yellow-legged frogs across the Sierra Nevada.

Only time will tell whether the Conservation Strategy meets these important goals.

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The Changing View of Pesticides as a Driver of Frog Declines

Pesticides have long been hypothesized to be drivers of amphibian declines in the Sierra Nevada. In the early 1970s, Lawrence Cory and colleagues published a study showing that DDT residues could be detected in mountain yellow-legged frogs throughout the Sierra Nevada, and they suggested that this was the result of DDT applications in the Central Valley. Since then, a myriad studies have detected many additional pesticides in numerous media in the Sierra Nevada, including water, lake sediments, air, snow, rain, fish, and frogs. 

The hypothesis that pesticides could be the cause of frog declines is rooted in the observation that declines observed during the 1980s and 1990s were most severe close to the Central Valley but populations in the High Sierra seemed to be relatively healthy. In an effort to test the pesticide hypothesis, in the mid-1990s, Gary Fellers and colleagues moved southern mountain yellow-legged frogs (Rana muscosa) from Sixty Lake Basin near the Sierra Nevada crest (where frogs were still abundant) west to the Tablelands area of Sequoia National Park where frogs had disappeared a decade earlier due to unknown causes. During this study, pesticide concentrations made in Sixty Lakes Basin and Tablelands indicated that levels were generally higher in the Tablelands area. The frog populations translocated to the Tablelands declined rapidly to extinction, a result at least consistent with the pesticide hypothesis. 

In 2007, Carlos Davidson and I published a paper showing that the distribution of mountain yellow-legged frogs across the central and southern Sierra Nevada was correlated with a distance-weighted metric describing the amount of pesticides applied upwind. This provided additional suggestion that pesticides might be involved in the decline of mountain yellow-legged frogs, but the evidence was correlative and based on the untested assumption that the variable describing the amount of pesticides applied upwind was in fact a good predictor of contaminant levels across the high country. As such, the role of pesticides in causing the mountain yellow-legged frog's decline remained largely a possibility based on circumstantial evidence.

During the past year, David Bradford and colleagues have published three papers that provide for the first time detailed field measurements of concentrations of dozens of pesticides across Sequoia-Kings Canyon National Park. Collectively, these papers cast doubt on the idea that pesticides are an important driver of amphibian declines in the high elevations of the Sierra Nevada. First, concentrations of all detected chemicals were extremely low, averaging in the low parts-per-billion in lake sediments and tadpoles, and 10 picograms/m3 in the air. For reference, one part-per-billion is roughly equivalent to a single drop in an Olympic-sized swimming pool, and a picogram is one-trillionth of a gram! Second, there was no relationship between measured pesticide concentrations and distance to the Central Valley, indicating that the pesticide metric that Carlos and I used in our paper was likely not a good predictor of pesticide exposure. Third, there was no correlation between the occurrence of mountain yellow-legged frogs and measured pesticide concentrations. 

So, these latest studies suggest that pesticides are unlikely to be playing an important role in amphibian declines in the high elevation portions of the Sierra Nevada. Whether such effects could be occurring in lower elevation habitats that are closer to the Central Valley and that therefore receive higher levels of airborne contaminants remains possible, although still largely untested. 

Bradford, D. F., E. M. Heithmar, N. G. Tallent-Halsell, G.-M. Momplaisir, C. G. Rosal, K. E. Varner, M. S. Nash, and L. A. Riddick. 2010. Temporal patterns and sources of atmospherically deposited pesticides in alpine lakes of the Sierra Nevada, California, U.S.A. Environmental Science and Technology 44:4609-4614.

Bradford, D. F., K. Stanley, L. L. McConnell, N. G. Tallent-Halsell, M. S. Nash, and S. M. Simonich. 2010. Spatial patterns of atmospherically deposited organic contaminants at high elevation in the southern Sierra Nevada mountains, California, USA. Environmental Toxicology and Chemistry 29:1056-1066.

Bradford, D. F., R. A. Knapp, D. W. Sparling, M. S. Nash, K. A. Stanley, N. G. Tallent-Halsell, L. L. McConnell, and S. M. Simonich. 2011. Pesticide distributions and population declines of California, USA, alpine frogs, Rana muscosa and Rana sierrae. Environmental Toxicology and Chemistry 30:682-691 (PDF).

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Disappearing Frogs and Shifting Baselines

I've studied mountain yellow-legged frogs for the last 15 years, all in the High Sierra, the last stronghold of these beasts. As a consequence of my experiences, when I think of mountain yellow-legged frog habitat in the Sierra Nevada I think of lake basins in the alpine and subalpine zones. But scientists who came before me, including Joseph Grinnell and Richard Zweifel, would have had a very different view. Back in their time, they found abundant mountain yellow-legged frog populations in streams at 6000' in the Ponderosa Pine belt of the western Sierra, in the expansive meadows of the unglaciated Kern Plateau, in the lakes, ponds, and streams in the Lake Tahoe watershed, in streams in Nevada's Carson Range, and in the far northern reaches of the historic range, in streams as low as 2000' on the Plumas National Forest. 

Most of these mountain yellow-legged frog populations are gone now, pushed aside by reservoirs, water diversions, introduced trout, and disease. The people who remember frogs in those places are mostly gone too. Luckily, they left us with field notes containing detailed descriptions of what they saw and collections of frogs in jars on museum shelves. Those relics serve as indelible reminders of the places these frogs once occupied and provide an unchanging reference point against which to judge the current situation and the success of future conservation efforts. 

I was recently assembling a data set of historic frog localities, and it was that data set that reminded me of just how ubiquitous mountain yellow-legged frogs once were. These records provide an amazing glimpse into a nearly-forgotten past. For example, in 1911 Joseph Grinnell and his survey team worked their way up the South Fork Kern River, describing the vertebrate fauna that they encountered and collecting the specimens that now reside at the U.C. Berkeley Museum of Vertebrate Zoology. In Monache Meadow, field notes record the presence of mountain yellow-legged frogs and also note the impacts caused by intensive livestock grazing. As they moved upstream, they saw mountain yellow-legged frogs in abundance in Templeton and Ramshaw Meadows, and at Big Whitney Meadow, at the headwaters of Golden Trout Creek, they observed Swainson's Hawks feeding on the seemingly ubiquitous frogs. At the nearby Rocky Basin Lakes, Grinnell had this to say:

"There are great numbers of apparently full-grown frogs around the shores of the lakes. The conspicuous thing about them is their extreme wariness. They jump into the water and dive quickly into the deepest holes within reach when one is yet fully 10 yards from them. There is a shower of frogs in advance of a person as he walks along the beach. They must have some nimble and persistent enemy."

That is a sight I would have loved to see, but the point of this isn't to romanticize the past. Instead, it is to recognize how quickly we forget what once was and replace it with a view based on our own experiences. Every human generation replaces what the previous generation knew to be true with their own version of reality, producing a series of shifting baselines through time. It is only the field notes and collections of those who came generations ago that remind us of what the world really looked like 100 years past. As someone who has hiked all over the High Sierra studying frogs, I thought I knew this frog well. It took Grinnell's journals to once again remind me of how narrow my own understanding is and of how much we've lost.
 
Back to The Mountain Yellow-legged Frog Site.

Lessons from the Plight of Frogs in Southern California

Researchers and managers from California and Nevada held their annual Amphibian Populations Task Force meeting January 6-7, 2011, this time in Yosemite Valley. With more than 100 attendees, the meeting once again provided a great opportunity to hear about the status of myriad frog conservation projects and catch up with colleagues. For me, the most insightful talk was that by Adam Backlin, the USGS scientist who with Robert Fisher (also with USGS), has been leading efforts to restore southern mountain yellow-legged frog populations (Rana muscosa) in the Transverse and Peninsular Ranges in southern California. This group of populations was listed as endangered under the U.S. Endangered Species Act in 2002.

Starting with only 150 frogs scattered across several populations and mountain ranges, the efforts to keep southern California R. muscosa from going extinct have begun to produce promising results. The removal of non-native rainbow trout from a reach of Little Rock Creek has allowed the resident R. muscosa population to begin to expand. The recovery of this population is still in its early stages but the fact that this population has increased to approximately 50 frogs from just a handful since fish removal is a very promising start. 

Thanks to the efforts by staff at the San Diego Zoo, researchers now have access to captive-bred R. muscosa for use in reintroductions. Reintroductions using this captive stock were conducted for the first time in 2010 so it is still too early to know the outcome of these efforts. But just having the captive colony available to allow reintroductions is a huge step forward. 

The insight from Adam's talk that really hit home for me was the necessity of active management to restore R. muscosa. A hands-off approach of protecting habitat and hoping for the best wasn't sufficient to stem the decline of this group of populations. This decline was slowed only by very intensive interventions. As we try to halt the decline of mountain yellow-legged frogs in the Sierra Nevada, there is an important lesson to be learned from the southern California efforts. That is, we can't rely simply on a hands-off approach to accomplish our goal. Unfortunately, it has been my experience that the hands-off approach is increasingly the one being relied on. 

As the mountain yellow-legged frog in the Sierra Nevada has disappeared from more and more of its native range, the response by managers has been to increase the protections afforded the remaining populations. In some cases, that has meant that populations are off-limits for research. I understand and generally support these protections but they aren't enough. For example, it is critically important that we also continue to test reintroduction methods and conduct experiments to improve our understanding of the frog-chytrid fungus interaction. I fear that with the continuing decline of the mountain yellow-legged frog and its eventual listing under the state and federal Endangered Species Act, our ability to conduct this critical research will be increasingly restricted. 

I hope we can learn an important lesson from the southern California experience.

Back to The Mountain Yellow-legged Frog Site.