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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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.

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Captive-bred Frogs Released into the Wild for the First Time

The southern mountain yellow-legged frog (Rana muscosa) inhabits lakes, ponds, and streams in the southern Sierra Nevada and southern California. The southern California Distinct Population Segment (DPS) was listed as "endangered" under the federal Endangered Species Act in 2002. This DPS currently contains fewer than 200 adult frogs and these remaining populations are at extreme risk of extinction due to a myriad of threats.

In response to the perilous status of this southern California DPS, scientists from the U.S. Geological Survey and San Diego Zoo have been working to develop an indoor captive breeding population the could eventually produce sufficient offspring for release into the wild. In an effort to stimulate frog breeding, this spring captive adult frogs were refrigerated for several weeks to simulate winter conditions. Once temperatures were increased frogs quickly began breeding, resulting in the production of numerous egg masses. 

In mid-April several of these egg masses were moved to a creek within the James San Jacinto Mountains Reserve, a reserve managed by the University of California. This is the first time that captive-bred mountain yellow-legged frogs have been released into the wild, and represents an important milestone in the recovery of frogs in this DPS. Time will tell how well the released animals survive. 

In addition to aiding the conservation of mountain yellow-legged frogs in southern California, these efforts have also produced a wealth of information regarding the breeding of these frogs in captivity. Whether we'll ever need these techniques for restoring mountain yellow-legged frogs in the Sierra Nevada remains to be seen but it is nice to have these methods already worked out. I continue to believe that one of the highest conservation priorities for Sierra Nevada frogs is to develop several outdoor captive populations of frogs in artificial ponds at an accessible location. Such populations are much less expensive to maintain than indoor captive populations (frogs don't need to be fed, water doesn't need to be changed, etc.) and would provide lots of offspring for use in research and conservation. All we need is a few ponds. Efforts to identify suitable ponds are ongoing.


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Once Upon a Time....

I remember with crystal clarity the day I realized the impact that the amphibian chytrid fungus (Batrachochytrium dendrobatidis - Bd) was having on mountain yellow-legged frogs in the Sierra Nevada. It was July 2000 and my field crew and I were surveying lakes and ponds along the Monarch Divide and Cirque Crest for amphibians and fish. I'd been as excited as a little kid to get into this area and see some of the most remote lakes in the Sierra, places where several years earlier a backcountry ranger had made observations of many mountain yellow-legged frog populations. When the trip was over 20 days later I felt like I'd been hit over the head with a hammer. The future of frog restoration in the Sierra Nevada had just gotten a lot more complicated than I ever imagined it would be.

Up until that trip the available data on Bd and its impacts was still sparse and remained an abstraction to me. The observations made by Dave Bradford 20 years earlier of frog die-offs in western Sequoia National Park were worrisome but were surrounded by enough uncertainty regarding the cause that I wasn't paying those observations much attention. Afterall, for the past five years I'd surveyed hundreds of lakes and the effects of fish were as clearcut as could be. But there were a few lakes that I'd run across during all of those surveys that did give me pause. There were those lakes near Pavilion Dome that contained fabulous frog habitat but in which I found either no frogs or only the decaying carcasses of frogs that had died the previous winter. And that lake between Lake Basin and Dumbbell Basin where I'd seen lots of frogs during a backpack trip in the early 1990s but by the time we surveyed that site there wasn't a frog to be found. These observations nagged at me but still lacked any broader context. In contrast, my recent analyses of survey data from more than 2000 lakes had clearly shown the negative effect of fish on frogs, and early results from two fish removal experiments conducted by me and by Vance Vredenburg showed dramatic increases in the frog populations at these sites just a few years after fish removal. Restoration of frog populations wasn't going to be easy because fish were so ubiquitous but at least we had the tools to reverse the decline of the mountain yellow-legged frog. To my eyes, the future looked bright.

The first lake I surveyed on that Monarch Divide trip was at the head of the Gorge of Despair. Looking down on the lake from above I could only smile. There should be gobs of tadpoles in that warm cove on the north side of the lake, I thought, and adult frogs will be sunning by the hundreds on those granite slabs near the outlet. An hour later I had finished the survey and could only shake my head. I'd found only four mountain yellow-legged frog tadpoles and had not seen a single adult. Even more alarming was that the tadpoles were clearly sick. We didn't have an accurate method of detecting Bd in those days but my notes on the datasheet that I filled out that day had an ominous tone: "All four tadpoles were large (~3 years old). The one individual I was able to catch had only a partial beak and no toothrows. Skin had a mottled appearance. Chytrid fungus?". Every subsequent day produced similar observations. In lake after lake where frogs had been abundant just a few years earlier we found either no mountain yellow-legged frogs or only a few tadpoles, all with mouthpart deformities suggestive of Bd infection.

Twenty days later, surveys completed and out of food, we hiked down the Copper Creek trail to Cedar Grove. On that long hot descent I struggled to put all of the pieces together. Frog die-offs in western Sequoia National Park in the 1970s and 1980s, healthy frog populations throughout the eastern portions of Sequoia and Kings Canyon National Parks, and now evidence of recent and ongoing die-offs along the Monarch Divide and Cirque Crest.... Could it be that Bd had been spreading from west to east across this part of the Sierra Nevada since the 1970s and that even those huge frog populations in places like Barrett Lakes Basin and Sixty Lake Basin might someday also succumb to this plague? The thought sent shivers down my spine and haunted me for years.

I called Dave Bradford the next day and before I could describe to him what we'd seen on our trip I somewhat immodestly blurted out, "I know what wiped out your frogs on the Tablelands - the chytrid fungus!". I don't know what he thought of my remark or the subsequent description of lake after lake with hardly a frog to be found, but I had seen the future of the mountain yellow-legged frog and it filled me with a profound sense of dread. All that I knew was about to change and the frogs that to me had become as much a part of the Sierra Nevada as the towering granite peaks were soon to be pushed aside by an unseen and unstoppable force.

And so it has come to be. Many of the lake basins where I counted thousands of frogs in the late 1990s are now frogless. When I walk along a lake shoreline no frogs jump into the water from their grassy hiding places. The shallows where tadpoles used to congregate by the thousands on warm afternoons, thrashing frantically in their retreat to deeper water when I approached, are calm and placid now. The mayflies and beetles are still in abundance in the nearshore waters and on the surface the lakes are as beautiful as ever, but these lakes are profoundly changed, perhaps forever. The same could be said of that idealistic young biologist....

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Involving the Public in Lake Restoration Programs

Sequoia-Kings Canyon and Yosemite National Parks are both preparing draft aquatic management plans that will describe several potential scenarios designed to restore native aquatic fauna while continuing to provide abundant opportunities for recreational fishing. Both plans will likely be released to the public in the next 6-12 months. These draft plans will provide an unprecedented opportunity for interested members of the public to have input into the Park-wide management of lakes and streams in these areas. Details on the Sequoia-Kings Canyon planning process are available here and those on the Yosemite plan are available here. Send a note to each Park (contact info in the above links) to be added to mailing lists for these planning processes. If you provided comments during the scoping period related to these plans you are already on their mailing lists.

On federal lands outside these national parks, the California Department of Fish and Game (CDFG) is currently developing watershed-based plans that describe the future management of fish (including fish stocking) and amphibians. These planning efforts have so far not been open to the public and completed plans are not publicly available. An example plan (for the Big Pine Creek watershed - near Bishop, California) is available here. This effort is being coordinated by CDFG senior biologists in Regions 2, 4, and 6 and overseen by Curtis Milliron. CDFG staff in Region 1 (includes Trinity Alps, Marble Mountains, Caribou Wilderness) and Region 4 (includes the western portion of the John Muir Wilderness and wilderness areas west of Kings Canyon National Park) have so far opted not to prepare management plans but I suspect that this will change in the near future. If you are interested in planning efforts in a particular area, I'd suggest calling the senior biologist responsible for that particular region. A map of the seven CDFG regions and associated contact information is available here.

On an unrelated note, since the new year I've strayed from my usual weekly posts due to obligations that have kept me away from my desk more often than not. I'll do my best to make future posts on Monday of each week.

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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.

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