Climate Change and Global Amphibian Declines

In 2006, Alan Pounds and colleagues published a paper in the journal, Nature, that claimed to show a link between global warming and the worldwide decline of amphibians. They argued that warming temperatures had allowed the emergence of chytridiomycosis, a disease caused by the amphibian chytrid fungus that has been wiping out amphibian species around the world. Despite providing only weak support for the role of climate change, the paper was splashed across the pages of hundreds of newspapers and magazines, all repeating the mantra that climate change was now a proven cause of amphibian declines.

This week, Karen Lips and colleagues published a paper in the journal, PLoS Biology, that challenges the conclusions of the Pounds paper. Although the media has portrayed the new paper as debunking the link between climate change and amphibian declines, the Lips et al. paper actually only refutes the analyses that Pounds et al. conducted and used to make their claim of a strong link between climate change and amphibian declines. This is an important distinction but one that as usual, is lost in the rush to create a catchy headline.

Both studies used similar data sets that describe the timing of amphibian declines in South America during the past several decades. However, the new paper reports that the link to climate change trumpeted by Pounds et al. is weakly supported at best. Lips et al. suggest that a more parsimonious explanation of the patterns of amphibian decline in South America is multiple introductions of the amphibian chytrid fungus into South America and subsequent spread across the continent. Lips et al. contend that there is no evidence for climate change driving this spread.

None of this detracts from the very real challenges posed by climate change to the conservation of amphibians around the world. It just highlights the important point that there is currently little support for the idea that global warming is responsible for amphibian declines.

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.

Has Frog Conservation Impacted Sierran Trout Fisheries?

There are a plethora of stories floating around the print media and the internet decrying the impact of mountain yellow-legged frog conservation efforts on Sierra Nevada trout fisheries. The on-the-ground realities paint a markedly different picture. In fact, one of the most remarkable outcomes of the increased research and management interest in mountain yellow-legged frogs is that backcountry trout fisheries are better managed today than they have been in decades.

With all due respect to the many capable biologists at the California Department of Fish and Game (CDFG), the CDFGs management of backcountry waters has been haphazard at best. Until recently, millions of fingerling trout were stocked into thousands of lakes every summer using airplanes, without any consideration given to whether those introductions were actually necessary to maintain trout populations. Fish population surveys that would have provided information on what stocking level, if any, was appropriate, were rare to nonexistent. This data-free management led to hundreds of lakes being stocked repeatedly despite the fact that the majority of these lakes harbored self-sustaining trout populations. When the CDFG halted the stocking of some of these self-sustaining trout populations, the populations showed no change in trout density and actually showed slight increases in fish size (see 2004 paper authored by Armstrong and Knapp in the Canadian Journal of Fisheries and Aquatic Sciences - available here). So, for years the CDFG was essentially just throwing many of those fingerling fish away. At a cost of $0.25-0.50 per fingerling, this resulted in the waste of millions of dollars.

After ignoring backcountry waters for more than 50 years, the decline of the mountain yellow-legged frog finally forced the CDFG to take Sierran lake management more seriously. Under the leadership of biologists like Curtis Milliron, the CDFG recently undertook a detailed inventory of thousands of lakes and as a result finally had the data necessary to make science-based stocking decisions. Although the backcountry lake stocking program remains archaic in many respects, the CDFG has at least taken a very important step in the right direction. However, it is important to remember that concern over the mountain yellow-legged frog drove these management changes, changes that have benefitted Sierran trout fisheries.

I still think that the CDFG has some important lessons to learn from Sequoia, Kings Canyon, and Yosemite National Parks. These parks terminated all fish stocking within their borders in the early 1990s, and anyone who has spent time exploring these park lakes knows that the majority of previously-stocked lakes continue to provide outstanding angling opportunities, all at no cost.

Sometimes the best things in life are in fact free....

Back to The Mountain Yellow-legged Frog Site.

Contaminants in Western National Parks

Airborne contaminants are suspected of contributing to the declines of amphibians, including the mountain yellow-legged frog in California's Sierra Nevada. Research on this important topic has been hindered by a lack of information on what contaminants are actually present and at what concentrations.

The final report of the Western Airborne Contaminants Assessment Project (WACAP) was released on February 28. Entitled, "The Fate, Transport, and Ecological Impacts of Airborne Contaminants in Western National Parks (USA)", this report is an eye-opener. The six year study focused on eight core parks and 12 secondary parks, stretching from Noatak National Preserve in northern Alaska to Big Bend National Park in southern Texas. Samples of air, snow, water, lake sediments, lichens, conifer needles, and fish were sampled for dozens of current-use pesticides, historic-use pesticides, industrial/urban compounds, combustion by-products, and heavy metals. The resulting dataset allowed analyses at an unprecedented spatial scale. For the sake of brevity, I'll summarize just those results from the three national parks in the Sierra Nevada, Sequoia-Kings Canyon (SEKI) and Yosemite (YOSE).

More pesticides were detected in SEKI than in any other park, and concentrations of current and historic-use pesticides were among the highest for all parks. Values for YOSE were generally somewhat lower. The source of most of these contaminants is believed to be the intensively-agricultural Central Valley, located just upwind. In SEKI, concentrations of the current-use pesticides, chlorpyrifos and dacthal, were particularly high. Samples of lake sediments confirmed that most pesticides first appeared at detectable levels in the 1950s, soon after they were first registered for use in the U.S. Concentrations of historic-use pesticides (e.g., chlordanes and DDT) generally decreased following bans on their use in the U.S. in the 1970s and 1980s, but concentrations of other contaminants (e.g., several current-use pesticides, PCBs) continue to increase. Using "contaminant health thresholds", the study concluded that in some cases concentrations of pesticides and mercury in the nonnative brook trout collected from the SEKI study lakes were high enough that consuming these fish could cause health problems in wildlife and humans.

Reading through the details of all of the contaminants found in the various samples, its easy to forget that the study is reporting results for national parks, those "crown-jewels" set aside from development to provide examples of intact ecosystems. Fulfilling this mission was a lot easier when threats were local (e.g., logging, mining, etc.). In the case of airborne contaminants drifting into our national parks from distant sources, it is clear that the Park Service mission will be increasingly difficult to fulfill. If regulating current-use pesticides within the U.S. isn't enough of a challenge, what does the Park Service do about contaminants originating in even more distant locales (e.g., China)?

After finishing reading the report, I couldn't help but think of that photograph of Earth taken from the moon - that precious blue, green, and white marble floating through the blackness of space. Traditional management boundaries (e.g., countries) will be increasingly irrelevant as we attempt to mitigate impacts generated by industrial societies across the globe. As with greenhouse gases, controlling airborne contaminants will only be possible if we can work across national borders for the benefit of Earth.

Back to The Mountain Yellow-legged Frog Site.