Lessons from the Plight of Frogs in Southern California

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

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

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

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

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

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

Back to The Mountain Yellow-legged Frog Site.

Impacts of Fish Stocking on Willow Flycatchers - Really?

As opening day for trout fishing season approaches, stories in the local papers often dwell on impending issues that might affect the number of fish stocked and stocking locations. Last year the stories focused primarily on issues surrounding the court order that mandated that the California Department of Fish and Game (DFG) prepare an environmental impact report detailing the effects of its fish stocking program. This year the stories have focused almost exclusively on the concern that the presence of willow flycatchers could preclude fish stocking. All of the media stories that I've read on this issue have failed to provide much context for this issue, focusing instead on how outside environmental groups are to blame for the current "crisis". The following is my attempt at clarifying how the willow flycatcher got wrapped up in the fish stocking issue and what the current DFG plans are related to this species. 

When I read the DFG fish stocking EIR-EIS I was quite surprised to see the willow flycatcher listed as a "decision species" ("decision species" were defined as those species potentially affected by hatchery and stocking programs). My surprise stemmed from the fact that there were no published studies suggesting such impacts on willow flycatchers. Furthermore, the interim court order that was developed jointly by the Center for Biological Diversity, Pacific Rivers Council, and the DFG (the intent of which was to prevent harm to sensitive species while the EIR-EIS was being written) focused only on fish and amphibians (13 and 11 species, respectively). So, how did the willow flycatcher end up in the EIR-EIS as a decision species? 

It turns out that it was the DFG that added the willow flycatcher to the decision species list, and without any prompting from environmental groups or the public at large. The rationale was basically that trout and willow flycatchers both depend on insect prey for a large proportion of their diets. Because the introduction of trout into mountain lakes dramatically reduces the biomass of aquatic insect larvae and the subsequent emergence of adult forms of these aquatic insects, the DFG reasoned that this reduction in adult aquatic insects could reduce prey availability for willow flycatchers. The willow flycatcher was on the DFG "radar screen" because it is listed as "endangered" under the California Endangered Species Act. 

The possibility that trout stocked into aquatic ecosystems could affect adjacent terrestrial ecosystems is a fascinating area of ecological study, and recent research in the Sierra Nevada shows that stocked trout have in fact altered the distribution and foraging habits of the Gray-crowned Rosy-Finch, one of the few species that nests in the alpine zone. This soon-to-be-published study provides evidence that trout-containing lakes had 98% fewer mayflies than did neighboring fishless lakes, and that Rosy-Finches were six times more abundant at fishless lakes than at fish-containing lakes as a result (mayflies make up a significant fraction of Rosy-Finch diets during the emergence period). However, it is a stretch to extend these Rosy-Finch findings to willow flycatchers, but that is exactly what the DFG did. 

In the EIR-EIS the DFG suggested that impacts of trout on willow flycatchers were possible, and proposed to mitigate these impacts by conducting a "pre-stocking evaluation" at each mountain lake that receives hatchery trout and that lies within the range of the willow flycatcher. As stated in the EIR-EIS (page 4-100), "Under the protocol, each stocking location shall be evaluated in a stepwise fashion to determine whether interactions between stocked trout and willow flycatchers may occur and to evaluate the potential for trout stocking to result in an (sic) substantial effect on willow flycatchers. If such an impact is determined likely, then DFG shall either cease stocking at that location or develop and implement, prior to stocking at that location, an ABMP". (ABMP = Aquatic Biodiversity Management Plan).

With the EIR-EIS finalized in January of this year, the upcoming opening of the trout fishing season is the first in which all fish stocking is required to meet the guidelines specified in the EIR-EIS. The range of the willow flycatcher includes the eastern Sierra Nevada so technically no lakes can be stocked in preparation for the season opener unless a pre-stocking evaluation for willow flycatchers has been conducted, and until a few weeks ago no such evaluations had been conducted for stocked waters anywhere in California. And how can evaluations be conducted when most mountain lakes are still surrounded by snow and it will be weeks before willow flycatchers arrive to breed? The DFG has been scrambling to figure this out and the ensuing confusion has generated a slew of rumors, including how the Center for Biological Diversity forced the DFG to include the willow flycatcher in the EIR-EIS and how the willow flycatcher is being used as an excuse by bureaucrats in Sacramento (including DFG bureaucrats, in some version of the rumors) to shut down the fish stocking program. That these rumors have little basis in fact has not stopped the local media from reporting and elaborating on the rumors and innuendo. 

So, here is my take on all of this. While I applaud the DFG for acknowledging that fish stocking impacts likely extend beyond the water's edge and can in some cases impact songbirds and other terrestrial predators, it is ill-advised to change fish stocking management without a scientific rationale. There are no data suggesting that willow flycatchers are negatively impacted by fish stocking. The current lack of evidence certainly does not indicate that no such impacts are occurring, but the lack of any scientific evidence makes designing effective mitigation essentially impossible. I would have much preferred a more cautious approach in which the DFG acknowledged the potential for impacts of fish stocking on willow flycatchers and committed to studying the issue over the next year. Subsequent management actions and mitigation could then have been designed based on the results of the accumulated evidence.


I never thought I would criticize the DFG for being overly aggressive in developing mitigation strategies to reduce impacts of fish stocking. Go figure.

Back to The Mountain Yellow-legged Frog Site.

Trout Impacts and Stocking Controversies - Beyond California

Much of the recent research on impacts of trout stocking has focused on aquatic ecosystems in California. However, a research program in Maine is now showing just how pervasive these impacts are. Most of Maine's naturally fishless lakes (and there were thousands of them historically) have now been stocked with numerous fish species, including brook trout, and all indications are that these introductions have had similar effects as those documented in California's Sierra Nevada and elsewhere - the disappearance of amphibians and conspicuous invertebrate taxa. The New York Times ran a story last week that provides an interesting overview of what the Maine research is turning up.

On the opposite coast, the practice of trout stocking continues to cause controversy in North Cascades National Park. This is the only national park in the country in which fish stocking is still allowed, but after many years of debate about the practice and detailed scientific study it appears that trout stocking may be on its way out. A recent Associated Press story provides the details.

Back to The Mountain Yellow-legged Frog Site.

Trout Impacts in California's Trinity Alps

When it comes to impacts of introduced trout on aquatic ecosystems, the Sierra Nevada is by far the best-studied such ecosystem in the world. However, an increasing number of studies are now being conducted elsewhere and results from this research make it clear that broad impacts are a common consequence of trout introductions into montane habitats. In recent years, a research group at the Forest Service Redwood Sciences Laboratory in Arcata has published several studies showing that introduced trout have severe impacts on a wide range of aquatic amphibians native to mountains in the Klamath bioregion, including the Cascades frog, Pacific treefrog, and long-toed salamander.

In a study just published in Freshwater Biology, Karen Pope and colleagues extend this past research by focusing on impacts to lake-dwelling invertebrates. Using a replicated whole-lake experiment conducted in the historically fishless Trinity Alps, they described changes over a three-year period in the emergence of aquatic insects from lakes in which (1) trout had never been introduced, (2) stocking of nonnative trout continued during the study, (3) stocking was suspended, and (4) stocking was halted and trout populations were removed using gill nets. Trout removal caused rapid increases in aquatic insect biomass over the three-year study period. Insect emergence was low in both the stocked lakes and stocking-suspension lakes because trout densities remained relatively high in lakes assigned to these treatments. Therefore, trout introduced into these naturally fishless lakes caused significant reductions in the biomass of native invertebrates and these taxa recovered quickly following trout removal.

The focus of the study by Pope and colleagues on insect emergence helps to emphasize a key point which is that trout impacts on lake-dwelling invertebrate communities aren't likely to be restricted to the lakes themselves. Adult forms of aquatic insects emerge from lakes and become available to a wide range of terrestrial predators and scavengers, including reptiles, birds, bats, and ants. Therefore, the reductions in insect emergence due to trout introductions could impact terrestrial species and the functioning of terrestrial ecosystems. Our increasing understanding of the connections between aquatic ecosystems and the adjacent terrestrial ecosystems is a fascinating area of study and provides a more complete picture of how pervasive the effects of trout introductions can be.

For additional information on the impacts of introduced trout on amphibians in the Klamath bioregion, check out the following papers:

Welsh, H. H., K. L. Pope, and D. Boiano. 2006. Sub-alpine amphibian distributions related to species palatability to non-native salmonids in the Klamath mountains of northern California. Diversity and Distributions 12:298-309 [link].

Pope, K. L. 2008. Assessing changes in amphibian population dynamics following experimental manipulations of introduced fish. Conservation Biology 22:1572-1581 [link].

Pope, K. L., J. M. Garwood, H. H. Welsh Jr, and S. P. Lawler. 2008. Evidence of indirect impacts of introduced trout on native amphibians via facilitation of a shared predator. Biological Conservation 141:1321-1331 [link].

Back to The Mountain Yellow-legged Frog Site.

Trout Impacts on Yosemite Streams

Most research on the impacts of nonnative trout on aquatic habitats in the Sierra Nevada have focused on lakes, in part because these are the habitats favored by the declining mountain yellow-legged frog. This research has shown dramatic changes to vertebrate and invertebrate species composition caused by trout predation on the larger, more conspicuous taxa. Trout also alter nutrient cycling in these lake habitats as a consequence of the changes in species composition.

A study by Dave Herbst and colleagues, just published in Freshwater Biology, shows very clearly that impacts of introduced trout on Sierran streams are similar to those documented for lakes. Herbst et al. compared the invertebrate communities, algal cover, and algal biomass in 21 paired streams in Yosemite National Park, one stream of each pair containing introduced trout and the other member of the pair remaining in a natural fishless condition. Densities of 10 out of 50 common invertebrate taxa were significantly reduced in the trout-containing compared to the troutless streams, and these taxa tended to be conspicuous forms whose native habitats are primarily at high elevation above the original range of trout.

Reductions in species richness in the trout-containing streams caused significant increases in algal cover and biomass compared to levels in troutless streams.
Increases in algae are likely a consequence of grazing invertebrates being reduced in the presence of trout and consequent reductions in herbivory. These indirect effects (trout reduce the density of grazing insects, reduction in grazers causes an increase in algal biomass) are in agreement with numerous other studies conducted on the effects of trout on streams all around the world.

The findings of this study serve as yet another example of the considerable impacts of trout introductions on Sierra Nevada aquatic ecosystems. Given the almost complete absence of watersheds anywhere in the Sierra Nevada that haven't been stocked with trout, it is clear that we need to think about how to restore at least some entire watersheds to their historic fishless condition. That is no small undertaking.

Back to The Mountain Yellow-legged Frog Site.

Global Amphibian Declines - The Movie

During the past year filmmaker Allison Argo and her team have been traveling around the world to film declining amphibians and find out from scientists what can being done about it. In addition to filming in Panama and the southeastern U.S., Allison's team also spent a few days with my research group while we conducted research on Sierra Nevada yellow-legged frogs in Yosemite National Park. The resulting film, "Frogs: The Thin Green Line" will be shown for the first time on April 5 (this Sunday) on PBS. Allison's previous films on amphibian declines (The Last Frog), declining shorebirds (Crash: A Tale of Two Species), and other wildlife-related topics were extraordinarily good, so I suspect that this latest film will be well worth watching. Hopefully Allison didn't include the footage of me falling into the pond.... On 3/31,the film's creators posted a podcast from "behind the scenes". Check it out.

If you do watch the film, feel free to post your reviews and thoughts here.

Now to the task of finding a friend who owns a TV....

Back to The Mountain Yellow-legged Frog Site.

New National Geographic Story on Amphibian Declines

Writer Jennifer Holland and photographer Joel Sartore have created a masterful story on the global amphibian decline phenomenon, just published in National Geographic magazine. The situation surrounding the mountain yellow-legged frog is described in the story, and Joel's photographs of live and dead Rana muscosa from Sixty Lake Basin bring this animal's plight into a sad focus. Check it out.

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The Politics of Trout Removal - A Global Phenomenon

I've written a fair bit lately about controversies surrounding trout stocking and trout removal. A theme running through many of these posts is that the politics of trout management strike an emotional chord with many members of the angling community, and sometimes those emotional responses get in the way of science-based management decisions. Although I've focused my posts on this topic specifically on the Sierra Nevada, an email I received recently made it clear that the situation we face in the Sierra Nevada is not unique. Geoff Heard is a PhD student in the Department of Zoology at La Trobe University in Victoria, Australia and had this to say:
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Dear Roland:

I have just been reading your Frog Blogs, and felt I must drop you a line. I have been aware of your work with Rana muscosa for sometime - I'm undertaking a PhD on the metapopulation dynamics of the endangered growling grass frog in Melbourne, Australia, and specifically, the impacts of urbanization on those dynamics.

Growling grass frogs like it warm, so they generally don't mix with trout, and thankfully that means I don't butt heads with the trout lobby. However, your situation with Rana is remarkably similar to one here in Victoria. Our case involves the spotted tree frog (Litoria spenceri), an endangered species that lives in mountain streams and has been shown to be very sensitive to trout predation (and suffering from the additive effect of chytridiomycosis). We had a concerted push a few years back to eradicate trout at two remnant L. spenceri sites, but the proposal was terminated by the trout lobby. Just as you describe, a few particularly vocal folk created an uprising by the fishing community, despite the fact that the proposal involved only small sections of two of the state's hundreds of trout streams, and that these sections are basically unfishable (narrow streams, densely vegetated, and containing only small fish). It created so much heat that the relevant official shelved the proposal and gagged the relevant scientists. And the spotted tree frog? Its decline continues to be monitored, but the most easily implemented and arguably most effective recovery action we know of remains off-limits.

So I wanted to congratulate on your great work, and encourage you to push on. Your work will not only benefit Rana, but also adds valuable weight to calls here in Oz for the case of the spotted tree frog versus trout to receive another (hopefully fairer) hearing.
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Ah, the politics of trout removal.... It is good to know that we are not alone here in California in our interest in maintaining populations of nonnative trout in virtually every habitat where they could possibly survive regardless of the consequences to all of those useless native species. Sigh.

Back to The Mountain Yellow-legged Frog Site.

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 www.nps.gov/yose/parkmgmt/aquatic.htm.

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Hope for Frogs in Southern California?

The southern mountain yellow-legged frog (Rana muscosa) has declined precipitously during the past century (check out www.mylfrog.info 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.

Fish Impacts on Frogs - the Tip of the Iceberg

The removal of trout populations from lakes and streams in California to restore mountain yellow-legged frogs (see http://www.mylfrog.info/threats/introducedfish.html) has generated a fair bit of controversy over the years. Much of the controversy stems from differences of opinion about the degree to which introduced trout are a primary cause of mountain yellow-legged frog declines, and therefore whether such removals in fact benefit frog populations. These are important debates, but miss the bigger picture entirely. That is, introduced trout have dramatic impacts not just on amphibians, but on aquatic ecosystems in general, and frogs are only one component of many in these ecosystems.

Numerous studies have shown that trout introduced into naturally-fishless habitats fundamentally alter the way these ecosystems function. Trout introductions change nutrient cycles and algal biomass, eliminate (or greatly reduce the abundance of) conspicuous invertebrates and amphibians, and sever connections between aquatic and adjacent terrestrial ecosystems. As an example of this latter effect, ongoing research indicates that aquatic insects emerging from lakes and streams are important prey for a host of terrestrial predators, including birds. Nonnative trout eliminate many of these aquatic insects via intense predation, and as a consequence alter the distribution of birds. These impacts are widespread in California's wilderness areas and national parks, areas set aside to protect natural values and processes. As such, these ecosystem-wide impacts are impossible to ignore.

Finding solutions that effectively mitigate the unintended consequences of fish introductions will require stepping back from a narrow fish-frog focus and taking a broader view that acknowledges that frogs are but one facet of a many-faceted issue.

Back to The Mountain Yellow-legged Frog Site.