December 31, 2008

Editorial About Court-ordered Fish Stocking Suspension

Today's San Francisco Chronicle contains an editorial (page B-7) on the recent court ruling that suspended fish stocking in some California water bodies in 2009 (for background see my 11/21/08 Frog Blog post). I wrote this piece as a counterbalance to the many stories on this topic printed recently in newspapers that decried the stocking suspension as having major negative consequences for local economies and fisheries. My prediction? Neither will be true.

Back to The Mountain Yellow-legged Frog Site.

December 29, 2008

The Angling Community's Dark Side

For thirty years I was passionate about fly fishing and carried a fly rod and a box of hand-tied flies wherever I went in wild places throughout California and the West. As a kid, fishing connected me to aquatic habitats and led me on a life-long pursuit of an endless list of ecological questions: Why did some lakes harbor a few large fish and others many small fish? What species of mayfly was that hatching in June in low elevation lakes in Yosemite? Why did I rarely find mountain yellow-legged frogs co-occuring with introduced trout in Sierran lakes? What invertebrates used to occur in these lakes before trout introductions? My enthusiasm for fly fishing was eventually tempered by the results of my own research that showed how dramatically fish introductions had altered the lakes and streams of the Sierra Nevada. After the passage of Assembly Bill 7 in 2005, the bill that required that a larger portion of fishing license dollars be spent raising hatchery trout, I finally gave up fly fishing entirely, no longer able to justify buying a fishing license and in doing so directly supporting the California Department of Fish and Game's (CDFG) stocking practices.

Today I often find myself at odds with the majority of California's angling community, a majority that often rails loudly at any efforts to modernize the CDFG stocking program and protests any proposal to restore native amphibians by removing selected nonnative trout populations. The majority's most vocal spokesmen (yes, they are all men) use newspapers as their bully pulpit to stir their angling readers into a froth over a wide range of angling issues, including the recent stocking moratorium in some California waters (see my December 1, 2008 post for an example). In doing so, they have repeatedly failed to recognize changing public sentiment that increasingly favors protection for endangered species and wild lands, and have refused to acknowledge that fish introductions have resulted in widespread impacts to aquatic ecosystems. This "head in the sand" approach is leading to an ever-increasing reliance on put-and-take stocking programs and to the view that California's lakes, streams, and rivers are little more than glorified hatchery raceways where we can dump thousands of hatchery-reared trout without negative consequences to the resident trout and to the native vertebrate and invertebrate fauna.

During all of this debate and rhetoric, a commonly-voiced sentiment is one that has anglers as the "original environmentalists", caring deeply for the habitats that sustain their quarry. Perhaps that is true, but I sure don't see much evidence of it these days. In fishing-related chat rooms (e.g., High Sierra Topix) it is common to find posts claiming that introduced trout have no negative impacts on native biodiversity, that the claim of fish effects on mountain yellow-legged frogs is a hoax perpetrated by wacko scientists (like yours truly), and urging anglers to take fish stocking into their own hands and move fish into the few lakes that remain
fishless. Such rhetoric will do nothing to improve California's fisheries.

In our haste to catch fish, it seems that we've forgotten that the quality of fishing is intimately connected to the health of the ecosystem. The decline of mountain yellow-legged frogs shouldn't be seen as a threat to fishing but as an indicator that all is not well in aquatic habitats of the Sierra Nevada. Should we care that trout introductions have impacted a large number of native taxa, from Callibaetis mayflies to mountain garter snakes to Gray-crowned Rosy Finches? I think so, because even from the most angler-centric view declines in these species indicate the loss of important trout prey. If we claim to love the Sierra Nevada so much, how can we not care about these impacts?

California's angling community could be a powerful agent for change - for healthy habitats and better fisheries - if it could shelve the rhetoric and roll up their collective sleeves to do the hard work of coming up with a plan to manage California's fisheries, wildlife, and habitats for a sustainable future.

Back to The Mountain Yellow-legged Frog Site.

December 12, 2008

Frog Restoration - the State of the Science

Numerous mountain yellow-legged frog recovery projects have been conducted in the last five years, with more in the planning stages. Virtually all of these projects relied on the removal of nonnative trout and most have met with stunning success. As a result of this work, there is now an abundance of information available on the details of how to remove nonnative trout. But how do we go about selecting sites for restoration? What makes the ideal restoration location?

The mountain yellow-legged frog restoration projects conducted to date have had as their goal increasing the amount of fishless habitat available to an existing frog population. These target frog populations are often small and relegated by the presence of trout to marginal habitats (e.g., shallow ponds). In these projects, site selection was straightforward: choose sites that (1) are in close proximity to existing frog populations, (2) contain high quality frog habitat, and (3) have the appropriate characteristics to allow fish population removal using mechanical means (gill netting, electrofishing). Criterion 1 ensures that mountain yellow-legged frogs will be able to recolonize the restoration site following fish removal. For Criterion 2, high quality habitat is generally characterized as lakes deeper than 3 m (10'), located at elevations below 3600 m (11800'), and surrounded by other suitable habitats including fishless lakes, ponds, marshes, and low-gradient streams (see Knapp et al. 2003 for details). Criterion 3 requires that there are no upstream fish populations and that fish from downstream locations are prevented from moving into the site by natural barriers on the interconnecting streams. In addition,
the chance of successful fish removal is increased by limiting lakes to those of small to moderate size (<20 style="font-style: italic;">Batrachochytrium dendrobatidis - "Bd") into the Sierra Nevada has the potential to considerably complicate restoration site selection. Most restoration projects conducted so far have been in areas in which Bd has not yet arrived. In areas where Bd is present, additional site selection criteria will likely be necessary to maximize the chances of successful frog restoration. In particular, we need to understand the conditions that limit Bd and thereby allow the growth and persistence of frog populations. Bd grows best at water temperatures of approximately 20 degrees C (70 F) and ceases growth above 30 C and below 4 C. In landscapes in which Bd is now ubiquitous (e.g., Yosemite National Park) we are currently studying how temperature regimes affect disease outcomes in frog populations. For example, do temperature effects on Bd growth rates result in increased frog survival in high elevation (i.e., cold) habitats compared to those at low elevations? Is frog survival increased when frogs have access to warm-water habitats such as marshes in which temperatures often exceed 25 C? Answers to such pressing questions are critically needed and we are working feverishly on these studies. Given the ongoing spread of Bd across the Sierra Nevada, the information provided by this research should help guide the selection of sites for future frog restoration projects.

Despite the typical focus of fish removal projects on the mountain yellow-legged frog, we can't lose sight of the fact that trout removal benefits not just frogs but a diverse community of vertebrate and invertebrate taxa. I maintain that having at least some fishless lakes and streams in each watershed across the Sierra Nevada is the most foolproof way to ensure the persistence of these native taxa. Sometimes that will mean removing trout from a lake even if frog recovery is unlikely.

Back to The Mountain Yellow-legged Frog Site.

December 1, 2008

DFG Releases List of 2009 Stocking Locations

In response to the recently-finalized interim stocking court order (see 11/21/08 post), on November 24 the California Department of Fish and Game (CDFG) released lists of California water bodies that either will or will not be stocked between now and the January 11, 2010 release of CDFGs draft fish stocking EIR/EIS. What struck me when I looked over the lists is how few waters state-wide will have their stocking allotments temporarily suspended. Of the 838 waters on the lists, stocking will continue in 91% during the interim period (761 waters will continue to be stocked, stocking in 77 waters is temporarily suspended). This hardly seems cause for alarm.

And yet, as seems always to be the case, several individuals have done their best to inflame the angling community. A
November 30, 2008 story by Tom Stienstra, the outdoor writer for the San Francisco Chronicle, tops the list of irresponsible reporting on this issue. Given Tom's consistent "damn the native species - stock the fish" perspectives (see my 10/17/08 post for one example), I'm hardly surprised. In his recent article, Tom blasts the interim stocking agreement as heralding the end of fishing in many of California's best angling destinations. His article repeatedly asserts that fish stocking at these sites is gone forever, conveniently failing to acknowledge that the stocking moratorium will affect only 77 waters across all of California and only in 2009. Furthermore, given that many of the waters affected by the moratorium are backcountry lakes stocked with fingerling trout, a one year stocking moratorium will have no adverse impacts on these fisheries. This kind of reporting is simply irresponsible and does California's angling community a grave disservice.

Of course, after years of involvement with fish stocking issues I'm used to this sort of junk reporting. About 10 years ago the CDFG proposed removing trout from two lakes in the Eastern Sierra's Big Pine drainage to facilitate the recovery of mountain yellow-legged frogs. Despite the fact that trout fisheries in the majority of the lakes in this drainage were not affected, stories in local and regional newspapers screamed for months about how the removal of trout from these two lakes would have serious negative effects on the area's fisheries and on local economies. Those fish removals are long since complete, and I've seen nary a report of any negative impact whatsoever. And the frogs are thriving. Go figure....

Back to The Mountain Yellow-legged Frog Site.

November 21, 2008

Agreement Reached on Interim Fish Stocking Restrictions

The California Department of Fish and Game (CDFG), Center for Biological Diversity, and Pacific Rivers Council have spent the last two weeks developing interim fish stocking restrictions that will be in place until the CDFG finishes their stocking EIR/EIS on January 11, 2010 (see 11/12/08 post for background). According to a press release issued by the environmental groups, an agreement on stocking restrictions was reached this past Wednesday and will likely be finalized by the Court on Monday.

So, how will stocking practices be affected by the order? The agreement states that fish stocking will be suspended during this interim period in (1) water bodies where surveys have indicated the presence of sensitive native fish and amphibian species (e.g., California golden trout, Santa Ana sucker, mountain yellow-legged frog, Cascades frog), and (2) water bodies that have not yet been surveyed for sensitive species. The just-reached agreement adds a few exemptions to this general stocking moratorium, including CDFG-permitted fish stocking conducted by private entities, stocking that is conducted for research or education (e.g., the CDFG Classroom Aquarium Education Program), legally-mandated mitigation stocking (e.g., stocking of salmon smolts below dams), the CDFG anadromous fish enhancement stocking program, and stocking of most artificial impoundments.

The interim stocking restrictions will have minimal impact on the Sierra Nevada for a couple of reasons. First, large portions of the Sierra Nevada are located within national parks (i.e., Sequoia, Kings Canyon, Yosemite) where stocking was banned in 1991 (as an aside, these national park waters continue to provide some of the best fishing in the State). Second, nearly all water bodies in the Sierra Nevada were surveyed for sensitive species in recent years and stocking allotments have already been modified to avoid stocking habitats that contain these native species. Outside of the Sierra Nevada, the most obvious impact of the agreement will likely be in northern California (e.g., Trinity Alps) where the CDFG has been particularly slow to improve their outdated fish stocking program and continues to stock trout into habitats containing Cascades frogs and long-toed salamanders. Those practices are now prohibited so we can expect some reductions in the number of water bodies stocked in this area.

These interim stocking restrictions have two important consequences. First, they will limit impacts of stocking on sensitive native species until the completion of the fish stocking EIR/EIS. Second, the interim stocking restrictions will provide additional impetus to the CDFG to keep the EIR/EIS process on track to meet the January 2010 deadline. Without the proverbial kick in the pants that the stocking restrictions provide I suspect that the EIR/EIS process would have dragged on for years. And third, they provide clear evidence of the value of proactive management whereby the CDFG conducted sensitive species surveys at thousands of lakes over the past decade and developed watershed-based management plans to better balance fish stocking practices with the conservation of native species. As a result of this proactive approach, these areas are exempt from the interim stocking restrictions.

Finally, although I see little evidence of this so far I am hoping that these restrictions and the subsequent EIR/EIS will provide an opportunity for the public to take a careful, open-minded look at the CDFG stocking program. Although California's angling public seems to buy the line that more fish stocking makes for better fishing, it is time to scrutinize that paradigm. Evidence to date actually suggests quite a different story. For example, research conducted in the High Sierra showed that most stocked lakes actually harbor self-sustaining trout populations and stocking (conducted at considerable expense) had no effect on trout density. So, in these hundreds of lakes stocking was just a waste of angler dollars. Studies in Montana conducted in the 1960s and 1970s indicated that stocking of catchable trout into rivers and streams actually caused decreases in overall trout densities. Based on the results of these studies, in 1974 Montana stopped all stocking of flowing waters (to large protests from anglers) and the result was drastic increases in trout populations (see Montana Outdoors story for details).

Clearly, a long, hard look at California's fish stocking program is long overdue.

Back to The Mountain Yellow-legged Frog Site.

November 12, 2008

Court Considers Interim Fish Stocking Measures

As I discussed in my 4/18/08 post, in late 2006 the Pacific Rivers Council and Center for Biological Diversity sued the California Department of Fish and Game (CDFG) to compel the agency to complete a fish stocking Environmental Impact Report (EIR). In Spring 2007, the court agreed that an EIR was necessary and required that a draft environmental document be completed by the end of 2008.

Now with the 12/31/08 deadline looming and the CDFG apparently having made little progress toward completing the EIR, the agency petitioned the court to extend the completion date to 1/10/2010. In response, the Pacific Rivers Council and Center for Biological Diversity argued that the extension should not be granted unless interim stocking guidelines are put into place to minimize impacts of stocking on sensitive species while the EIR is being written. Sensitive species of particular concern include the California golden trout, Santa Ana sucker, mountain yellow-legged frog, and Cascades frog.

On 11/7/08, the court ordered the CDFG into talks with the Pacific Rivers Council and Center for Biological Diversity to develop these interim measures. So, the parties have until 11/24/08 to negotiate an agreement that specifies where the CDFG can stock fish pending completion of the EIR.

Using a tactic that they've used repeatedly in the past, the CDFG issued a press release that seems an ill-considered attempt to stir up controversy, perhaps to strengthen their hand in the negotiations with the Pacific Rivers Council and Center for Biological Diversity. Responding to the court order, CDFG Director Donald Koch made the claim that a failure by the parties to reach an agreement could "stop altogether or significantly reduce its fish stocking programs", with significant impacts to local businesses and communities. This far overstates the Court's order which considers limiting stocking only where a handful of sensitive species are present.

What will it take for the CDFG to take seriously its obligations to minimize impacts of fish stocking to California's native fauna? The outcome of the negotiations will speak volumes about the CDFGs intent. Things could get interesting....

Back to The Mountain Yellow-legged Frog Site.

October 31, 2008

More About Climate Change and Amphibian Declines

The role of climate change as a driver of amphibian declines is a controversial topic. As I described in my 3/27/2008 post, an article by Pounds et al. in Nature suggested that climate warming in South America was responsible for the emergence of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) and subsequent catastrophic amphibian declines on that continent. These results have been challenged on several grounds, and in my view remain conjectural at best.

An article just published in the Proceedings of the National Academy of Sciences provides much clearer evidence that recent climatic anomalies have resulted in declines of amphibian populations. The authors report that six decades of climate data for Yellowstone National Park shows a trend of increasing temperatures and decreasing precipitation. These changes in temperature and precipitation have caused many of the ponds in the study area to dry up. This, in turn, has resulted in marked decreases in the number of sites occupied by three species of amphibians: blotched tiger salamander (Ambystoma tigrinum melanostictum), boreal chorus frog (Pseudacris triseriata maculata), and Colombia spotted frog (Rana luteiventris). These results are certainly of concern, but it remains to be seen whether these patterns hold up over the longer term.

Direct effects of climate change on amphibians due to consequent changes in habitat are likely to increase in severity in coming decades. Even the mountain yellow-legged frog, a species that requires permanent water bodies for successful breeding and overwintering, will likely be affected as what were once permanent lakes, ponds, and streams become ephemeral. Such changes could spell extinction for many populations of this already imperiled species.

Back to The Mountain Yellow-legged Frog Site.

October 24, 2008

Are Frogs Becoming Resistant to the Amphibian Chytrid Fungus?

The arrival of a new disease into a naive animal or human population usually results in strong impacts initially, but the severity of these effects often subsequently declines as the host animals develop resistance to the disease. Recent observations of amphibians persisting following die-offs caused by the amphibian chytrid fungus (Batrachochytrium dendrobatidis - "Bd") has raised speculation that these post-crash amphibian populations, including those of the mountain yellow-legged frog, are resistant to Bd. Development of resistant populations would dramatically increase the likelihood of population persistence despite the presence of Bd, and would provide ideal source populations for reintroduction efforts.

However, are amphibians really developing resistance to Bd? Unfortunately, as of yet there is no evidence of this in mountain yellow-legged frogs or in other species. Mountain yellow-legged frogs taken from populations that are persisting with Bd and introduced into nearby lakes often experience Bd-caused die-offs within a couple years. Furthermore, frogs from persistent populations succumb to Bd when held in the laboratory under a wide range of environmental conditions. Both results indicate that frogs from persistent populations are clearly not resistant to Bd. So, if frogs aren't developing resistance, how do we explain the persistence of some populations following Bd outbreaks?

There are at least three explanations in addition to frog resistance to Bd. First, it is possible that Bd strains differ in their virulence and that infection by a less virulent strain allows persistence while more virulent strains cause extinction. Second, habitat conditions (e.g., water temperature) may influence the amphibian-Bd interaction, either by changing Bd virulence or by changing the amphibian immune response. For example, in warm climates where air and water temperatures stay in a range that is detrimental to Bd (above 30 degrees C), the effect of Bd may be much less severe compared to in cooler climates that are more favorable to Bd. Third, persistence of amphibian populations in the presence of Bd may simply be a consequence of density-dependent disease dynamics. If higher frog densities allow higher Bd densities ("positive density dependence"), then after a frog population crash Bd densities should decline. Under these conditions, it is possible that frogs would experience Bd infections of lower intensity, allowing frog persistence. This persistence may be short lived, however, because if frog density subsequently increase so too will Bd, likely resulting in another frog population crash.

All four of these explanations for frog persistence are plausible, but all remain speculative. We're working to understand the role that each of these might play in allowing frog persistence but with numerous field and laboratory experiments either underway or planned in the near future, we are likely several years away from definitive answers. With Bd having already caused massive declines of mountain yellow-legged frogs across their entire range, time is definitely not on our side.

Back to The Mountain Yellow-legged Frog Site.

October 17, 2008

Frog Fable #3 - Fish Removals Cause Frog Disease Outbreaks

I recently read a letter that stated that fish removals, far from benefiting mountain yellow-legged frogs, actually cause outbreaks of the amphibian chytrid fungus (Batrachochytrium dendrobatidis - "Bd"). The purported basis for this is essentially that fish removal causes frog populations to grow and that the resulting increased frog density boosts the likelihood of Bd outbreaks. Furthermore, by removing fish populations from clusters of lakes, frog dispersal between adjacent habitats is increased and this enhances Bd spread.

Ecological theory suggests the plausibility of the above-outlined scenario. However, a decade of field research in the Sierra Nevada provides absolutely no support for the idea that fish eradications cause Bd outbreaks.

This idea seems to have its origin in two sources, the first an article written by Tom Stienstra - the outdoor columnist for the San Francisco Chronicle - published August 17, 2003, and the second a scientific paper written by me and two colleagues published in 2007 (PDF). Both sources mention cases in which initial frog population increases following fish removal were followed by frog population crashes. So, let's look at both of these in turn.

To quote the key section of Tom Stienstra's piece, "The father, Don Vachini of Novato, and sons Jason and Matt had hiked eight miles over 11,000-foot Piute Pass and into Humphreys Basin, where several gorgeous lakes are set in granite pockets. They set up a base camp at Lower Desolation Lake, set at the timber line at 11,375 feet, then trekked another two miles cross-country to their favorite lakes at the foot of towering Mount Humphrey (sic), looming overhead at 13,986 feet. These lakes are cobalt blue with pristine clarity. On windless mornings, there is a perfect mirror image of the mountain on the lakes' surfaces. The surrounding landscape is stark batholithic granite, with pockets of ice and snow and a few scraggly pines. But Vachini shook his head, a hollow look in his eyes. 'Can you believe all the trout are gone from this magnificent water?' he asked. 'After 20 years of hiking into Humphreys Basin, it breaks my heart.' In a program that could become the prototype for hundreds of high Sierra lakes, all the trout have been netted out and killed at Vichini's favorite lake.... But last month, Roland Knapp of the Sierra Nevada Aquatic Research Laboratory made his own shocking discovery in Humphreys Basin: at Vachini's favorite lake, where all the trout were cleaned out to protect the frogs, all the frogs were suddenly gone, too. They were wiped out last winter by chitrid (sic) fungus, Knapp said."

Quite a dramatic outcome, isn't it? Unfortunately, Tom Stienstra fabricated this story.
Following the removal of fish from several small lakes in this part of Humphreys Basin, the frog population has thrived and in marked contrast to Tom Stienstra's vivid imagination, to date there has been no Bd-caused population crash. During my visit to this area in early September of this year, I counted more than 8000 tadpoles and 1500 adult and juvenile frogs, counts that continue the trend of a steep increase following fish removal. The above photo and the photo accompanying my October 10 post were taken immediately following this survey.

Which brings me to the article we published in 2007 (Knapp, R. A., D. M. Boiano, and V. T. Vredenburg. 2007. Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, Rana muscosa). Biological Conservation 135:11-20). This article focused primarily on the recovery of mountain yellow-legged frogs following fish removal in Humphreys Basin (John Muir Wilderness) and LeConte Canyon (Kings Canyon National Park). It also mentioned the important role played by Bd in limiting frog populations and in particular, the Bd outbreak in 60 Lake Basin (Kings Canyon National Park) a few years after fish removal and subsequent frog population increases in several lakes. This is decidedly not a case of fish removal causing the Bd outbreak, however. In fact, Bd is spreading across Sequoia-Kings Canyon National Park as a west-to-east moving front. Having arrived at the basin just west of 60 Lake Basin in the mid-1990s, I expected its arrival in the adjacent 60 Lake Basin by 2000. It took a bit longer than that, but in 2004 Bd outbreaks began in 60 Lake Basin and in the next four years spread across the entire watershed, reducing the mountain yellow-legged frog population to a fraction of its pre-Bd size. The first Bd outbreaks actually began in a portion of the basin that was most distant from the fish removal sites. Furthermore, Bd caused high mortality in all frog populations in this basin, regardless of frog numbers or density, providing another suggestion counter to the notion that larger frog populations are more susceptible to Bd outbreaks.

In summary, despite many years of data collection at numerous sites across the southern Sierra Nevada, there is no evidence that frog population recovery following fish removal causes Bd outbreaks. The long-term fate of the recovering frog populations in now-fishless lakes in 60 Lake Basin and elsewhere will provide the ultimate test of whether fish removal can benefit mountain yellow-legged frogs despite the presence of Bd. Until those results are in, let's stick to the facts as we currently know them. Wild extrapolation from these facts only results in the loss of credibility on the part of the person making the extrapolation.

Back to The Mountain Yellow-legged Frog Site.

October 10, 2008

Frog Fable #2 - Declines are Caused by Disease not Trout

The causes of global amphibian declines are hotly debated within the scientific community, but one of the best documented causes is the role of nonnative trout introduced into historically fishless lakes in the Sierra Nevada. (If you'd rather not take me on my word on this one, check out a 2003 review of the topic by Kats and Ferrer - Diversity and Distributions 9:99-110.) The conclusion that predatory trout play an important role is based on surveys of thousands of lakes across the Sierra Nevada (likely the most extensive lake survey ever conducted anywhere) and on experiments in which trout were removed from lakes and frog populations subsequently increased rapidly (click here for details). Collectively, the results from these studies are irrefutable: introduced trout have severe negative effects on mountain yellow-legged frogs and are directly responsible for the extinction of many frog populations.

The story of the mountain yellow-legged frog's decline became considerably more complex with the recent discovery that the extremely virulent amphibian chytrid fungus (Batrachochytrium dendrobatidis - "Bd") was spreading across the Sierra Nevada (and through other habitats around the world) and was causing widespread extinctions of mountain yellow-legged frog populations. Soon after these studies were published, I began to hear the misconception that these results "proved" that trout were in fact not responsible for the decline of the mountain yellow-legged frog. I beg to differ. The important role of Bd in causing declines in no way changes the obvious negative effect that nonnative trout have on mountain yellow-legged frogs. We know for certain that trout and Bd BOTH play important roles in driving this decline. For example, Bd is ubiquitous in Yosemite National Park but despite this surveys of all 3000+ of the Park's lakes and ponds showed a clear negative effect of nonnative trout on mountain yellow-legged frogs and other amphibians (Knapp 2005).

The current "state of the science" regarding the relative importance of Bd versus trout in causing frog declines isn't complete, but it does provide critical insights to guide restoration actions. Here is what I wrote in a recent peer-reviewed article (Knapp et al. 2007):

"... there are several reasons why fish eradication is likely to remain a critically important tool for restoring R. muscosa populations. First, patterns of B. dendrobatidis spread remain enigmatic and it is not clear that B. dendrobatidis will eventually spread to all R. muscosa populations. Second, although the arrival of B. dendrobatidis may reduce the benefits to R. muscosa populations conveyed by fish eradications, our understanding of B. dendrobatidis and its effects on R. muscosa is still far from complete, and fish eradications may in fact confer long-term benefits. For example, the presence of nonnative fish has relegated many R. muscosa populations to marginal habitats that only support small frog populations or have increased the degree of R. muscosa population isolation. As a result of small population sizes and isolation, these populations may have a lower likelihood of surviving stochastic events such as disease outbreaks. If some R. muscosa populations do persist following a disease outbreak, this creates the potential for host-pathogen evolution that may over time favor more resistant frogs and/or a less virulent strain of B. dendrobatidis.... As such, the eradication of fish populations is likely to be a key element of any attempt to conserve and restore amphibian populations inhabiting these montane lentic environments, regardless of whether other anthropogenic factors also exert a controlling influence on these populations."

The only way to determine with certainty whether fish eradications can in fact benefit Bd-infected mountain yellow-legged frog populations is to conduct experimental fish removals in areas where Bd is known to be present. Precisely such experiments are currently being conducted in Yosemite and Kings Canyon National Parks, but several years of frog surveys will be necessary before strong conclusions are possible.

In closing, we need to move beyond overly simplistic views ("Bd is the cause, not fish") of the complex situation regarding the decline of the mountain yellow-legged frog. Instead, all of us interested in the future of frogs and fish in the Sierra Nevada need to work together to craft solutions that are based on the best available science. Twisting the science to fit particular perspectives does not advance this cause.

Note: I'm currently away from my office so the posting of any comments submitted by readers will be delayed by several days. Thanks in advance for your patience.

Back to The Mountain Yellow-legged Frog Site.

October 3, 2008

Frog Fable #1 - Frog Disease is Spread by Researchers

Due to an extremely busy summer field season, it has been several months since I've had the luxury of a few days off. As regular readers have surely noticed, that lack of time has seriously limited my ability to continue with my usual weekly posts. But now, with fall in the air, my field season has concluded and I can once again return to a more sane schedule. So, you can look forward to weekly posts once again.

As an ecologist involved in efforts to restore mountain yellow-legged frog populations, I have the opportunity to read lots of comment letters submitted by members of the public in response to various frog-related agency projects. These letters are an important part of any democratic process, but some of the statements contained in these letters take undue liberty with the facts as we currently understand them. Given my firm belief that sound decisions designed to conserve biodiversity (and mountain yellow-legged frogs in particular) absolutely depend on decision-makers and the general public understanding the current "state of the science", I'll use my next several blog posts to clarify some of the most common misunderstandings.

As detailed on the Mountain Yellow-legged Frog Site, chytridiomycosis (the disease caused by the amphibian chytrid fungus, Batrachochytrium dendrobatidis) is associated with declines and extinctions of amphibians all around the world. Mountain yellow-legged frogs are highly susceptible to this disease and many recent disappearances of frog populations in the Sierra Nevada are attributable to chytridiomycosis outbreaks
(click here for details). Some people, perhaps concerned that the steady decline of the mountain yellow-legged frog will result in calls for additional removals of nonnative trout, have sought to pin the blame for this decline on the scientists studying the problem. Scientists, the argument goes, have been spreading the chytrid fungus from frog population to frog population during the course of their research.

On the surface, this seems a reasonable argument but it ignores several important facts. First, research in Australia, Central and South America, and California's Sierra Nevada indicates that the chytrid fungus is spreading as a distinct front and is moving into new areas at a very predictable rate. This uniform spread is not what would be expected if researchers (whose movements could perhaps best be described as haphazard) themselves were the agent of spread. Second, in the Sierra Nevada and elsewhere chytridiomycosis has spread into many areas that were never visited by amphibian researchers. And third, amphibian scientists around the world (including those of us working in the Sierra Nevada) adhere to a strict protocol of chemically disinfecting all of their field research gear between each visited water body or watershed.

A far more likely vector of the chytrid fungus is infected frogs moving between water bodies. In addition, adult stages of aquatic insects fly in great numbers from one water body to the next, and could be effective agents of disease spread. The half-baked notion that researchers themselves are spreading the amphibian chytrid fungus provides a convenient scapegoat but it doesn't hold up under even the most basic scrutiny.

Next week I'll discuss the common misconception that the discovery of the important role played by the amphibian chytrid fungus in causing mountain yellow-legged frog declines exonerates nonnative trout as a major cause of these declines.

Back to The Mountain Yellow-legged Frog Site.

September 7, 2008

Frog Sex - Part Two

In a previous post ("Frog Sex is a Strange Affair") I discussed the shenanigans that mountain yellow-legged frogs engage in during the breeding season. During a recent trip into the backcountry to survey frog populations, I was reminded of the peculiar sexual behaviors that these frogs display in the fall when frogs are obviously not breeding. With the arrival of shorter days and cooling water temperatures in late-August and September frogs start engaging behaviors normally associated with breeding, including calling and amplexus (above photo was taken two days ago). Seeing frogs engaging in these behaviors in the fall is rather odd since actual breeding is still nine months away. So, what are these frogs doing?

My guess is that they are "practicing" for the breeding season that will occur
next spring. This guess is based on the fact that most of the individuals showing these behaviors appear to be small males. Their small size suggests that they may have just attained sexual maturity and therefore have not yet participated in a breeding season. If true, it would be valuable to be able to "practice" calling and amplexing before next spring's breeding season. The individuals I watched a few days ago who were trying to amplex other frogs were certainly clumsy in their efforts. For example, the male shown in the above photo has placed his forearms in front of the forearms of the other frog instead of behind them. I watched this pair for several minutes, and it seemed that the amplexing individual needed all the practice he could get - what a bumbler!

With the return of ice and snow just a month or so away, the frogs may be using this short window in the fall to practice their breeding skills and thereby improve their chances of mating successfully in the spring.

I wonder if other amphibian species show similar pre-breeding behaviors....

Back to The Mountain Yellow-legged Frog Site.

August 14, 2008

Color Variation in Mountain Yellow-legged Frogs

I've visited a lot of mountain yellow-legged frog populations this summer during my surveys conducted throughout the Sierra Nevada, and have been amazed (as always) at the variation in frog color patterns that I've seen. Sierra Nevada yellow-legged frogs (Rana sierrae) seem to have relatively invariant color patterns, with their characteristic dorsal dark blotches and smaller cream-colored spots on a dark brown background, yellow bellies, and dark speckling under the chin. In some populations the cream-colored spots are absent and the dark blotches are more obvious, but this variation is pretty subtle. In contrast, Southern mountain yellow-legged frogs (Rana muscosa) have wildly variable colorations. The most common dorsal color pattern is one with prominent dark blotches on a tan background, cream-colored bellies, and no spots under the chin. However, I just surveyed an R. muscosa population in which the frogs had an R. sierrae-like dorsal coloration and bellies that were markedly orange and semi-transparent (to the point where internal organs were distinctly visible through the skin!). At another site, the R. muscosa were highly variable within a population, some frogs having cream-colored or silverish vermiculations across their backs and others having the dorsal colorations more typical of R. sierrae.

What is the source of this variation? Does it have a genetic basis, and if so why the occasionally high levels of within-site variation? Given that the ranges of R. muscosa and R. sierrae abut each other along the Monarch Divide and Cirque Crest in the southern Sierra Nevada (R. sierrae north of the divide/crest, R. muscosa to the south), why the color variation despite virtually identical habitat conditions? Clearly these differences in coloration are driven not simply by natural selection for effective camouflage. Instead, I suspect that the color variation we see across the landscape is a consequence of the post-glacial frog colonization histories of these different parts of the Sierra Nevada.

If only the frogs could talk, they'd undoubtedly have quite a tale to tell....

Back to The Mountain Yellow-legged Frog Site.

July 20, 2008

Aquatic Ecosystem Restoration in Yosemite National Park

During the past century, trout were introduced to thousands of naturally fishless lakes and streams throughout California's Sierra Nevada to create recreational fisheries. These introductions profoundly changed these aquatic ecosystems, often resulting in the elimination of numerous native species, including amphibians and large-bodied invertebrates. Today there is hardly a single watershed in the Sierra Nevada that still remains in its historic fishless condition.

Reversing some of the impacts caused by nonnative trout is a difficult challenge, and one that Sequoia-Kings Canyon National Park began to tackle a couple of years ago with the preparation of a Park-wide aquatic restoration plan. A draft version of this plan is scheduled for release to the public sometime this fall. Now Yosemite National Park is following suit. According to a recent news release, Yosemite will soon be preparing
a "High-Elevation Aquatic Resources Management Plan and Environmental Assessment", the purpose of which will be to "guide management actions by the National Park Service to protect Yosemite's diverse high-elevation aquatic ecosystems and to restore natural composition, structure and function to systems that have been disturbed by past or ongoing human activities".

The document will consider the removal of nonnative fish from selected areas of the Park, but will not include removal of fish populations using chemical methods (e.g., rotenone). This will be an interesting process to watch. Public comments are being accepted until July 25. More information is available at

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July 7, 2008

Frog Sex is a Strange Affair

I've been in the field for most of the last month and given that this is frog breeding season I've seen some pretty bizarre things related to this reproductive frenzy. But first, some background on mating in frogs. To mate, a male clasps a female with his powerful front legs that he wraps around the female just behind her front legs. To strengthen that grip, the male has nuptial pads on the thumbs of each hand that make it very difficult for the male to be dislodged when the digits from the front legs are interlocked around the female. This clasping of the female by a male is called "amplexus", and in frogs serves two purposes. First, it allows the male to "guard" the female from other males, thereby ensuring the reproductive success of the amplexing male. Second, it positions the male to allow him to fertilize the eggs as the female releases them.

As the photo above vividly shows, amplexus is not a simple matter of a male gently holding on to a female for several minutes while she looks for a place to lay her eggs. In the photo, a male-female pair is in amplexus and three additional males are doing their darnedest to pull the pair apart. If successful, this would afford one of the other males a chance to amplex the female. These battles can go on for hours, and often result in deep abrasions on the ventrum of amplexed females from the male nuptial pads. In rare cases, during extended battles the female can actually be drowned by all of the competing males.

Wrestling with other males for hours for access to females is only the beginning of what goes on in the frog world during the mating season. On my last backcountry trip, a male I was measuring had new amplexus scars, suggesting that he was recently amplexed by another male and that additional males were battling it out for access to him! My guess is that the original male was so jacked up on hormones that he failed to realize that he had amplexed another male instead of a female, and seeing an amplexing pair the other males piled on. Even more bizarre is the not uncommon observation of males amplexing dead frogs, often frogs that have been dead for weeks or even months.

Just another example of how sex on the brain causes all kinds of bizarre behaviors....

Back to The Mountain Yellow-legged Frog Site.

June 21, 2008

A Hopeful Find

In this age of declines in global amphibian populations, signs of hope are often hard to come by. On my recent research trip into Yosemite National Park, I made one of those rare hopeful finds. My field crew and I were hiking through a forested low elevation portion of the Park and approached a small stream flowing through a meadow. As I neared the stream, a Sierra Nevada yellow-legged frog jumped from the shore into a nearby pool and disappeared. I'd crossed the stream at this very spot numerous times before and had never seen an amphibian. Had I imagined the frog? A quick search upstream and downstream turned up numerous other adults, subadults, and tadpoles. Had they been here all along? If so, why had we never found them previously? If they hadn't been here all along, where did they come from? In all of our survey work, we'd found no other Sierra Nevada yellow-legged frog populations anywhere in the vicinity. Regardless of the answers to these questions, finding a new frog population is always a rare and welcome discovery. It certainly made my day.

More in a week when I'm back from my next trip into the backcountry.

Back to The Mountain Yellow-legged Frog Site.

June 13, 2008

Another Day, Another Frog Die-off

I'm out in the field this week and won't be able to post anything substantive as a result. However, this photo gives you an indication of what we found on our first trip - lots of dead frogs killed by chytridiomycosis. I've seen these die-offs many times, but still get a knot in my stomach whenever I stumble across another one. More next week.

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June 6, 2008

The Increasing Inadequacy of the Endangered Species Act

The Endangered Species Act (ESA) was signed into law in 1973, and is responsible for bringing numerous species back from the brink of extinction. However, 35 years after its signing the ESA is increasingly showing its age. In 1973, most species endangerment was the result of local impacts that were relatively easy to identify and the resolution of which was generally straightforward. For example, Brown Pelicans were driven into decline by increased DDT concentrations in the environment. DDT was banned in the U.S. in 1972, and Brown Pelican populations have rebounded dramatically.

Although the current declines of many species have similarly identifiable causes, an increasing number have complex causes that are challenging the relevance of the ESA. The polar bear and the mountain yellow-legged frog provide two examples of the problems posed by this complexity. The polar bear was recently listed as "threatened" under the ESA due to current and projected declines resulting from global warming. Unfortunately, the ESA was designed to deal with local threats such as habitat destruction, not global threats like climate change, and therefore lacks the tools necessary to deal with challenges as complex and far-reaching as global warming. Even if the ESA contained tools that would aid in reducing carbon dioxide emissions in the U.S., the ESA of course lacks the ability to regulate emissions in other countries.

The mountain yellow-legged frog (Rana muscosa, Rana sierrae) that inhabits the mountains of California presents a related but different challenge for the ESA. These two species have declined by more than 90% during the past century. Once the most common vertebrate across much of their range, they are now one of the rarest. R. muscosa in southern California was listed as "endangered" in 2002 and the listing of R. muscosa and R. sierrae in the Sierra Nevada was found to be "warranted" in 2003. The primary threat to these species through the 1970s was likely the introduction of nonnative trout into historically fishless lakes and streams. That threat is now been compounded by the emergence of the disease, chytridiomycosis, that is decimating mountain yellow-legged frog populations once thought to be secure because of the local absence of introduced fish.

If introduced fish were the only threat to mountain yellow-legged frogs, a recovery plan presumably would identify water bodies from which fish should be removed, and those removals would allow frog populations to rebound. Simple, right? Given the known importance of disease in driving current declines, what tools does the ESA give us to deal with this threat? Very few, if any. The biggest challenge caused by chytridiomycosis is that we don't even know what caused the emergence of this disease. Was it human-caused (e.g., climate change) or was it caused by the natural evolution of a more virulent strain? Disentangling "natural" from human-caused stressors is already extremely challenging, and will become much more so in coming decades as subtle effects of climate change, contaminants, and ecosystem changes become ever-more pervasive.

In the case of chytridiomycosis, even if disease emergence was human-caused, we currently have no means of eradicating the disease. Therefore, many species being pushed toward extinction by chytridiomycosis are doomed, and yet the ESA provides no mechanism for triage. Alternatively, if chytridiomycosis is the result of a natural evolutionary event (which will be very difficult to show conclusively), should we try to counteract the effect of that natural event? If yes, how should we allocate scarce resources between species being driven to extinction by anthropogenic causes versus apparently natural causes?

Our inability to distinguish between natural and human-caused species declines and questions on how to respond to these types of declines will increasingly compromise our ability to halt the impending flood of species extinctions. In our ever more complex world, our only hope of slowing the rate of human-caused extinctions may be an international "Endangered Ecosystems Act". More about that pipe dream some other time.

Back to The Mountain Yellow-legged Frog Site.

May 30, 2008

Is Captive Breeding in the Mountain Yellow-legged Frogs Future?

In last week's post, I wrote about the captive breeding of amphibians in general, and this week I'll focus specifically on the mountain yellow-legged frog. With the ongoing decline of this species, the topic of captive breeding seems to come up at every meeting in which population recovery efforts are discussed. Although the debate about what role captive breeding can realistically play in the global amphibian decline crisis is heated and will likely continue for many years, efforts to develop a captive breeding program for mountain yellow-legged frogs have already been underway for several years.

In April 2005, the Conservation and Research for Endangered Species (CRES) group at the San Diego Zoo began a captive breeding effort with southern mountain yellow-legged frogs (Rana muscosa) obtained from the last population hanging on in the San Bernardino Mountains. The goal of the effort was to create an "integrated program of captive propagation, headstarting, and release that will ensure the long-term viability of the species in the wild". These frogs were taken into captivity following a fire that swept across the area, creating the very real threat that these last frogs could be lost during winter floods and debris flows. Ultimately, seven frogs were captured and transferred to the San Diego Zoo. Unfortunately, all seven died due to an unspecified disease.

A second chance to develop a captive frog population came along a year later. In August 2006, a U.S. Forest Service biologist observed
R. muscosa tadpoles stranded in drying stream pools in the San Jacinto Mountains. No suitable habitat was present in the vicinity to which the stranded tadpoles could be transferred, so all 82 tadpoles were collected and brought to the San Diego Zoo. According to a short article published in yesterday's Los Angeles Times, 62 of the tadpoles have metamorphosed into froglets. If these animals survive into adulthood, the plan is to keep some at the zoo as part of a captive breeding program, and the remaining animals will be released back into their original habitat.

Successful reintroduction into the wild is only possible if the original cause of population decline has been mitigated. Unfortunately, for mountain yellow-legged frogs in southern California's Transverse Ranges, the cause of decline remains obscure. Introduced trout have likely played a role (see my post from May 16, 2008), but the relative importance of other factors is unknown. With fewer than 150 mountain yellow-legged frogs remaining in the Transverse Ranges, the only way find out what the population-limiting factors are may be to carefully follow the fate of frogs once they are released back into the wild.

Clearly, the path to recovering this species will be a slow and uncertain one.

Back to The Mountain Yellow-legged Frog Site.

May 23, 2008

The Amphibian Ark: Good Intentions, Uncertain Outcomes

The Amphibian Ark is a conservation effort developed to implement the ex situ (i.e., captive breeding) components of the IUCN Amphibian Conservation Action Plan (ACAP). The mission of the Amphibian Ark is to "ensure long-term survival of species in nature utilizing short-term ex situ management of amphibian taxa for which adequate protection in the wild is not currently possible". Although it is very unfortunate that adequate protection in the wild is in fact no longer possible for an increasing number of amphibian species, this is a reality of our time. The recent global emergence of the amphibian chytrid fungus (Batrachochytrium dendrobatidis) has massively compounded this problem, and was a major impetus for the development of the ACAP.

The fact that many amphibian species are being driven to extinction is irrefutable. What actions will be most effective in preventing these extinctions remains very much an open question. The ACAP suggested a very important role for captive breeding, but is captive breeding a realistic solution? Hundreds of amphibian species are being driven to extinction by a myriad of factors including disease, habitat destruction, introduced species, and overharvest. Do we really have the resources to harbor even a fraction of these declining amphibian species in captivity? The ACAP provides some insights into the costs of captive breeding programs, and these figures are an eye-opener. The estimated 5-year cost to house 100 amphibian species in zoos is $41,000,000! Where is this money going to come from? Will it be siphoned away from already-scarce funds used for conservation efforts currently being implemented in the wild?

The idea of housing hundreds of species in zoos brings with it difficult issues that go well beyond financial considerations. One of the most important is what the fate of those captive populations will be. For species threatened primarily by habitat destruction, efforts at preserving pieces of habitat could be followed by release of animals back into the wild. However, the fact that disease is playing such an important role in causing global amphibian declines greatly complicates the role of captive breeding. For example, the amphibian chytrid fungus is spreading around the world, and once it is present at a site it is apparently there forever. Under this scenario, releasing disease-free animals back into the wild will not be an effective conservation strategy. The released populations will simply become reinfected and succumb. Numerous examples from the field of disease ecology indicate that the only solution to the effects of disease is evolution between host and pathogen. Putting amphibians into zoos and keeping them free of disease will halt the process of host-pathogen evolution, and will ensure that the captive populations will not have a chance of survival in the wild.

Another serious concern related to captive breeding is the unavoidable genetic effects on the captive population. These effects arise from the novel environment in which the animals are held, which will always be markedly different from that in the wild. These changes to the environment induce new selective pressures that can result in rapid changes to the animals themselves. A recent article published in the journal, Science, showed that steelhead trout raised in hatcheries had greatly reduced reproductive capabilities when released back into the wild. The reduction in reproductive capabilities accrued at the astounding rate of 40% per generation, so every generation had approximately half the reproductive capability of the previous generation. Based on these striking results, the authors concluded that "even a few generations of domestication may have negative effects on natural reproduction in the wild" and that "the repeated use of captive-reared parents to supplement wild populations should be carefully reconsidered".

There are no easy answers here, but there sure are enough difficult questions to give me pause when contemplating the role of captive breeding programs for hundreds of the world's amphibian species.

Back to The Mountain Yellow-legged Frog Site.

May 16, 2008

Hope for Frogs in Southern California?

The southern mountain yellow-legged frog (Rana muscosa) has declined precipitously during the past century (check out for details), and nowhere has this decline been more severe than in the Transverse Ranges in southern California. Mountain yellow-legged frogs are now extinct from 98% of the sites they formerly inhabited and were listed as Endangered in 2002.

For the past decade, Robert Fisher and colleagues (U.S. Geological Survey) have been studying the eight populations of mountain yellow-legged frogs remaining in southern California in a last-ditch effort to prevent their extinction. Although the causes of the frogs' decline remain relatively poorly understood, trout introduced into the streams inhabited by the frog have been suspected as playing a role for many years. As such, the California Department of Fish and Game (CDFG) recently stopped stocking trout in those locations where mountain yellow-legged frogs were present. In addition, the CDFG began actively removing nonnative rainbow trout from one location (Little Rock Creek) to determine the effect of this removal on a remnant mountain yellow-legged frog population.

Surveys conducted in 2007 provide the first indication that these fish removals are beginning to have their desired effect (summary report available here). In 2000, a small population of mountain yellow-legged frogs was present above a natural barrier at the headwaters of Little Rock Creek, but were absent below the barrier (where trout were present). In 2001, the U.S. Forest Service built a fish barrier 1.5 km downstream of the natural barrier, and since 2002 the CDFG has been removing trout from the reach between the two barriers. Trout removals are conducted once per year via electrofishing.

In 2006, USGS scientists found a juvenile mountain yellow-legged frog in the trout-removal reach. In 2007, as many as seven mountain yellow-legged frogs were detected in the same area. The appearance of frogs coincided with the apparent elimination of trout from the upper portion of the trout-removal section.

Given these hopeful (although preliminary) results, the CDFG needs to immediately step up their fish removal efforts in Little Rock Creek. In recent years, fish removals have been conducted by CDFG volunteers and removal efforts have been limited to one two-day session per year. The electrofishing effort should be increased to include at least a few weeks of fish removals per year, and electrofishing could potentially be supplemented by efforts using gill nets placed into stream pools.

The CDFG deserves a lot of credit for the current Little Rock Creek frog recovery project, but has to redouble their efforts to carry the project to a successful conclusion.

Back to The Mountain Yellow-legged Frog Site.

May 9, 2008

Garter Snakes - The Anaconda of the Frog World

In last week's post, I wrote about the relative lack of food for mountain yellow-legged frogs at high elevation sites, and some of the tactics they use to fill their bellies despite this scarcity. Despite this disadvantage of high elevation sites compared to lower elevation sites where food is more plentiful, the high elevation habitats also have a distinct advantage - a virtual lack of predators, especially garter snakes.

Three species of garter snakes inhabit the range of the mountain yellow-legged frog, each in a very specific habitat niche and all with a strong affinity for water and for amphibian prey. The Valley garter snake (Thamnophis sirtalis fitchi) is found at elevations up to about 5,000'. The Sierra garter snake (Thamnophis couchi) is found at elevations of 5,000' to 8,000', and the mountain garter snake (Thamnophis elegans elegans - photo above) is found at elevations of 8,000' to 11,000'. These snakes congregate at water bodies containing amphibians, and mountain yellow-legged frogs are a major component of their diet.

Habitats above 11,000' are generally free of snakes, and it is in these highest elevation lakes that the densities of mountain yellow-legged frogs reach their peak. Densities of three frogs per foot of lake shoreline are not uncommon, and at such sites tadpoles by the thousands often aggregate in shallow, warm waters. These densities are a remarkable sight to behold when all other life forms are so scarce, and are in large part a consequence of a lack of predators. Not only are garter snakes absent, but so too are invertebrate predators such as large beetles that prey on tadpoles. Bears and coyotes might come by on occasion and eat a few frogs but their visits are relatively rare. And so, frogs have these
highest elevation alpine lakes largely to themselves.

Mountain yellow-legged frogs have evolved some interesting behaviors to reduce the risk of predation. For example, tadpoles reduce their swimming activity when confronted by the smell of a garter snake. In other amphibian species, the presence of predator scents causes tadpoles to develop a more streamlined body shape and a more powerful tail. It remains to be seen whether mountain yellow-legged frogs show similar developmental responses to predators.
Given that mountain yellow-legged frogs don't move much during their lives, I've often wondered whether frogs from low-elevation habitats have evolved anti-predator behaviors that are absent in frogs from the highest elevations.

Given that mountain yellow-legged frogs have coexisted with predators for millenia, you can bet that they have a host of tricks that we have not yet discovered to reduce their chances of become someone else's meal.

Back to The Mountain Yellow-legged Frog Site.

May 2, 2008

Frogs at 12,000 feet?

In the back of our minds, I think most of us have a picture of what frog habitat looks like, perhaps a warm pond filled with lily pads and logs. Given this preconception, it comes as quite a surprise to see mountain yellow-legged frogs basking by the thousands at lakes in the Sierra Nevada that lie well above timberline, some at elevations as high as 12,000' (3,660 m). How do they survive in these cold, stark conditions?

The fact that frogs are ectothermic, as described in my 4/25/08 post, plays an important role in allowing mountain yellow-legged frogs to flourish at high elevations. Given the cold water and air temperatures even in mid-summer, food requirements are relatively modest, allowing frogs to add the necessary fat reserves to get them through the long winter despite low densities of prey.

Despite the general paucity of food in this harsh environment, food is actually plentiful during short periods and mountain yellow-legged frogs take full advantage of this ephemeral abundance. In early summer (a few weeks after ice-out), mayflies and chironomids ("midges") transform from aquatic larvae into terrestrial winged adults and provide a brief dietary bounty for the frogs. The mayfly, Ameletus edmundsi, thrives in cold, high elevation lakes, and its emergence style makes it particularly vulnerable to frogs. Unlike many mayfly species that emerge well offshore, A. edmundsi crawls up onto a shoreline rock and emerges there. In lakes harboring mountain yellow-legged frog populations, I've watched frogs eyeing A. edmundsi larvae from the second they crawl out of the water and then engulfing the winged adult just as it completes metamorphosis. Midges provide a similar feeding opportunity for frogs. On windy days, chironomid adults aggregate in mating swarms on the lee side of boulders. Within minutes of these aggregations forming, mountain yellow-legged frogs will arrive and spend hours picking off chironomid adults when they land on the rock to rest.

During late summer, most aquatic insect emergences are over and mountain yellow-legged frogs depend more heavily on terrestrial prey. Anything crawling along the lake shore that fits in their mouths is fair game. I've watched grasshoppers get blown into the water, swim back to shore, and be eaten by a frog as soon as they crawl up onto a shoreline rock. Although mountain yellow-legged frogs generally spend their time right at the lake shore, some take advantage of another food source away from water: ants. Frogs will position themselves along ant trails and pick off the hapless ants as they pass by. The metamorphosis of Pacific treefrogs (Pseudacris regilla) from tadpole to froglet in late summer provides another food source. The froglets don't have the well-developed hopping skills of adults and make easy prey for the much larger mountain yellow-legged frog.

Despite the various tricks that mountain yellow-legged frogs employ to fill their bellies, food is scarce in this high elevation environment, especially when there are thousands of frogs at a lake all competing for the same limited food resource. And yet, these high elevation lakes offer the frogs an important advantage over lakes at low elevations: a lack of snake predators. More about that next week....

Back to The Mountain Yellow-legged Frog Site.

April 25, 2008

For The Frogs, It Is Still Winter

Here in the eastern Sierra Nevada, signs of spring are everywhere. After a winter during which the only common birds were Mountain Chickadees and Dark-eyed Juncos, a host of birds not seen for months are now in every bush and tree. The aspen and cottonwood trees are clothed in catkins, and the trunks of Jeffrey pines smell strongly of vanilla-scented sap. With all of these reminders that summer is on its way, I've been busy preparing for another field season studying mountain yellow-legged frogs up in the High Sierra. On a warm day down here at 7,000' it's easy to forget that for the mountain yellow-legged frogs in the high country it is still winter and will be for another month.

In the fall when the air turns cold and insect prey becomes scarce, mountain yellow-legged frogs retreat into the deep waters of lakes, coming to shore to sun only on the warmest of days. By late October, the lakes are skimmed with ice and by November or December the landscape is clothed in a thick blanket of snow. For the next seven months, the frogs live underwater in a world of near-freezing temperatures and complete darkness, breathing solely through their skin. Like many amphibians, mountain yellow-legged frogs capture prey primarily with their sticky tongues, but this method doesn't work underwater. So, for these seven months the frogs probably don't feed at all, living solely off of the fat reserves they accrued during the previous summer. Most mammals, including humans, die from starvation after a few weeks without feeding, and yet the mountain yellow-legged frog can survive without food for seven or more months! How do they do it?

This survival ability is a direct consequence of amphibians being ectothermic (often called "cold-blooded"), meaning that body temperature is controlled by factors outside of their bodies (e.g., air or water temperature). Body temperature of ectothermic animals controls metabolism, with body temperature and metabolism being positively correlated. During winter, the body temperature of mountain yellow-legged frogs is near the freezing point and their metabolism is therefore extremely low. As a consequence, their need for food is also greatly reduced. The mountain yellow-legged frog pushes this ability to survive without food to an extreme seen in few other amphibians. During winters with unusually heavy snowfall, lakes can thaw as late as August and then freeze over again in October. Under these conditions, mountain yellow-legged frogs can be without food for ten months and have only August-October to replenish their fat reserves for the next winter.

When spring finally comes to the high-elevation haunts of the mountain yellow-legged frog, lakes thaw and frogs crawl to shore in search of warmth, mates, and food. What has always amazed me when I've been at a lake during this time is that the frogs aren't particularly skinny. They haven't eaten anything for months and yet they are only slightly less plump than they were the previous fall.

I wish I could go months without eating. That ability would certainly make my backpack a lot lighter during the summer when I'm doing my frog research in the Sierra Nevada backcountry.

Back to The Mountain Yellow-legged Frog Site.

April 18, 2008

Dragging the Fish Stocking Program into the 21st Century

By the late-1990s, the California Department of Fish and Game (CDFG) was increasingly under fire for its failure to consider the impacts of its Sierra Nevada fish stocking program on native aquatic species, including the mountain yellow-legged frog. Despite an unprecedented effort by the CDFG to survey the thousands of lakes and ponds under their jurisdiction for amphibians and nonnative trout (and the resulting internal report describing widespread impacts of nonnative trout on amphibians), the CDFG never formalized any fish stocking guidelines designed to minimize impacts to Sierra Nevada ecosystems. I suppose the logic was that if there was no official CDFG policy, then the stocking program could not be held to account. Rumors of internal (unofficial) policy changes circulated for years, but it was clear that these guidelines were not being followed consistently across the Sierra Nevada. If changes were made to the fish stocking program, they were made behind closed doors and were never disclosed to the public.

Despite an overwhelming body of scientific evidence pointing to impacts of nonnative trout on Sierra Nevada lake ecosystems, the CDFG continued to claim that the stocking program was exempt from the provisions of the California Environmental Quality Act (CEQA). CEQA was signed into law in 1970 to ensure that projects carried out by public and private entities (including State agencies) were conducted such that significant effects on the environment were avoided or mitigated. As I wrote in a chapter in the 1996 Sierra Nevada Ecosystem Project final report (Volume 3, Chapter 8), the CDFG claim that the fish stocking program did not have the potential to cause environmental impacts and was therefore exempt from CEQA was clearly not justified.

Several environmental groups, particularly Trout Unlimited, Pacific Rivers Council, and the Center for Biological Diversity, repeatedly warned the CDFG that unless the fish stocking program was modified to reduce environmental impacts they would challenge the CEQA exemption that the CDFG had claimed for 35 years. Once again, denial ruled the day and stocking continued as usual. On October 5, 2006, the Stanford Law School Environmental Law Clinic sued the CDFG on behalf of the Pacific Rivers Council and the Center for Biological Diversity, requesting that all further fish stocking throughout California be halted until the CDFG complied with CEQA.

On May 4, 2007, the Court ruled that the CDFG fish stocking program is not exempt from CEQA and that the CDFG is violating CEQA by their failure to conduct an environmental review of the program (ruling available here). In response, the CDFG agreed to write an Environmental Impact Report for the stocking program by late 2008. So, for the first time in the history of this program the CDFG will finally have to disclose to the public the program's scope, impacts, and mitigations. I'm hopeful this disclosure will result in a fish stocking program that is more closely guided by the best available science. That can only lead to better management of California's recreational fisheries. It's too bad it took a lawsuit to achieve this end.

Back to The Mountain Yellow-legged Frog Site.

April 11, 2008

The Fish Stocking Program Loses Its Way

Following the end of World War II, the California Department of Fish and Game (CDFG) began experimenting with using airplanes to stock trout into High Sierra lakes. Following initial successes, this program was soon used to stock millions of fingerling trout into lakes in remote areas throughout the State. In the Sierra Nevada, the efficiency of aerial stocking allowed thousands of lakes to be stocked on a regular basis, including those too remote to have been stocked previously. As such, the aerial stocking program created abundant new opportunities for anglers, but also impacted the lakes and streams of the High Sierra on a scale not seen since the melting of the Sierran ice cap 12,000 years earlier. Mountain yellow-legged frogs, already in serious decline due to the smaller-scale fish stocking efforts that preceded the aerial stocking program, were now eliminated from hundreds of additional lakes. On national forest lands, where the CDFG had authority over fish and wildlife, virtually every water body that was suitable for trout was stocked, and mountain yellow-legged frogs were relegated to a handful of lakes that had for one reason or another never been added to the fish stocking list. In the Sierran national parks (Sequoia, Kings Canyon, Yosemite) where authority over fish and wildlife rested with the National Park Service, stocking was less intensive but still resulted in trout being introduced to the majority of water bodies.

Ironically, aerial fish stocking, a remarkable achievement in its time, led to the CDFG backcountry fish stocking program losing its way. Airplanes were a far more efficient means of stocking trout than the previously-used mules, and that efficiency brought with it a certain blindness. For example,
thousands of lakes were stocked every year or every other year without any thought being given to whether particular lakes needed to be stocked to provide angling opportunities. Some of these stocked lakes were so remote that they rarely received any human visitors. In other lakes, originally- introduced trout reproduced naturally in inlet and outlet streams and quickly developed self-sustaining populations. Ignorant of their self-sustainability, the CDFG added thousands of additional fingerlings with each stocking. Blinded by the success of the aerial stocking program, the program remained virtually unchanged for 50 years.

By the late 1990s, researchers studying amphibian declines in the Sierra Nevada and in other mountain ranges in the western U.S. were increasingly convinced that introduced trout were a major cause of frog disappearances. Surveys of thousands of water bodies in the High Sierra showed that the presence of trout greatly reduced the likelihood of finding mountain yellow-legged frogs and other vertebrate and invertebrate taxa. Furthermore, experimental removal of trout from a handful of lakes resulted in rapid recovery of mountain yellow-legged frog populations. With mounting evidence indicating that trout introductions had caused unintended but dramatic impacts to Sierra Nevada aquatic ecosystems, and with t
he potential listing of the mountain yellow-legged frog under the Endangered Species Act, pressure was building on the CDFG to modify the stocking program to reduce these impacts. After 50 years of tremendous public support, it was clear that the program had fallen victim to its own success.

Next week: How change finally came (or didn't come) to the stocking program....

For additional reading, check out the following papers (available at

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.

Armstrong, T. W., and R. A. Knapp. 2004. Response by trout populations in alpine lakes to an experimental halt to stocking. Canadian Journal of Fisheries and Aquatic Sciences 61:2025-2037.

Knapp, R. A., D. M. Boiano, and V. T. Vredenburg. 2007. Removal of nonnative fish results in population expansion of a declining amphibian (mountain yellow-legged frog, Rana muscosa). Biological Conservation 135:11-20.

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