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.

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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.

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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....

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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.

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 except 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 except 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 so 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.

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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 the 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 http://vesr.ucnrs.org/pages/knapp/publications/publications.html):

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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Fish Stocking in California - An Early History

My posts during the next few weeks will focus on the fish stocking program of the California Department of Fish and Game. This program provides important and cherished recreational opportunities, but has also caused unintended environmental impacts, including impacts to the mountain yellow-legged frog (www.mylfrog.info).

The practice of stocking fish has a long and interesting history. This worldwide tradition has its roots in a desire but us humans to improve the landscapes in which we find ourselves by adding something that we recognize and that has some obvious utility (i.e., food). We also seem to have a fascination with fish. These two predilections come together in the practice of stocking fish. To make sense of today's fish stocking practices in California, it is important to understand the history that underlies this program.

In California's Sierra Nevada, early settlers found that most of the streams and lakes near their homestead, mine, or logging camp were fishless, and the amphibians and invertebrates had no obvious value to those intent on carving their niche out of this wild landscape. And so trout that were native to lower elevations creeks and rivers were moved in buckets to fishless waters higher up the mountains, and those fish provided food and fun in those early hardscrabble days.

By the late 19th and early 20th century, the high country of the Sierra Nevada was earning the deserved attention of increasing numbers of adventurers, and those climbers and explorers brought with them the same predilections for trout as those that had homesteaded in the Sierra Nevada a generation earlier. In the High Sierra, they beheld a landscape entirely devoid of fish. "Correcting" this became a form of recreation unto itself and was undertaken with characteristic zeal. Individuals, fish-stocking clubs, hiking clubs (including the Sierra Club), and the U.S. military (which managed Sequoia, Kings Canyon, and Yosemite National Parks for a time) all contributed to this fish stocking mission, hauling trout into the high country using horses and mules (see photo) and moving fish between high country lakes and streams using cooking pots and coffee cans.

These early fish stocking efforts were loosely coordinated by the California Fish and Game Commission (the precursor to the current California Department of Fish and Game), but were rather haphazard affairs that took little notice of what species of trout had been stocked previously or even whether a particular lake was suitable for trout. The goal was simply to stock as many fishless waters as possible, and understandably the details were of little importance. By the 1940s, the many individual fish stocking efforts had been subsumed within a single agency that was responsible for managing Califoria's fish and wildlife: the California Department of Fish and Game (DFG).

Next week: how the California Department of Fish and Game's fish stocking program failed to keep up with changing times....

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