SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.2.2.8. Yosemite Toad (Bufo canorus)

The information below was extracted and summarized from the following reference: USDA Forest Service. unpublished. Draft Conservation Assessment for the Yosemite toad (Bufo canorous). USDA Forest Service, Pacific Southwest Region, Vallejo, CA. Detailed references can be found in that document. This section updates and supplements the information found in FEIS Volume 3, Chapter 3, part 4.4, pp. 218-219.

Habitat Requirements

The Yosemite toad has been found in a wide variety of high montane and subalpine lentic habitats including wet meadows, lakes, and small ponds, as well as shallow spring channels, side channels and sloughs. The species is most commonly found in shallow, warm water areas including wet meadows, small permanent and ephemeral ponds, and flooded, shallow, grassy areas and meadows adjacent to lakes. Some evidence indicates that toad populations may have been more abundant in lake environments than they are currently. Meadow habitats are often surrounded by lodge pole (Pinus contorta) or whitebark (P. albicaula) pines. Toads are more likely to be found in areas with thicker meadow vegetation or patches of low willows (Salix spp.).

Suitable breeding sites generally are found in shallow water at the edges of meadows, seasonally flooded pools of water within meadows, or in slow-flowing shallow spring channels, and runoff streams. Tadpoles also have been observed in shallow ponds and shallow areas of lakes. Short emergent sedges, few-flowered spike rushes, and other rushes often dominate breeding sites. In one study, breeding ponds were usually less than 12 inches deep. Persistence of water and warmer temperatures conducive to tadpole development contribute to successful recruitment. Researchers have found that toads preferred shallow breeding sites and tadpoles preferred warm shallow margins during the day. Thus, water depth and temperature appear to be important limiting factors in the survival of eggs and tadpoles.

The Yosemite toad is an explosive breeder, laying eggs at snowmelt over a short period of time. They emerge from winter hibernation as soon as snow melt pools form near their overwintering sites. Observed emergence times range from early May to mid June and breeding begins soon after emergence.

Metamorphs overwinter their first year in their natal meadow and appear to move upland mid-summer of their second year. In meadows, metamorphs and yearlings appear to be associated with willows and long sedges and grasses. Metamorphs can routinely be found throughout the summer months in moist and wet meadow areas, particularly where they meet the mudflat margins of their breeding areas.

After breeding, adults feed in meadow habitat or move into other aquatic habitat away from meadows such as headwater springs. Most studies have considered the toad to be diurnal but a recent telemetry study found them to be active at night.

One study found that adults have high site fidelity. Adults bred at the same ponds and, after breeding, tended to use the same one or two locations for daytime refuge. Some subadults moved from rearing ponds to different sites for breeding.

Overwintering habitat is poorly understood, but it is generally assumed that Yosemite toads overwinter in rodent burrows.

Historic and Current Range and Distribution

Yosemite toads are known from 292 sites throughout their historic range, 229 of which have been confirmed occupied since 1990. Known Yosemite toad locations by area is based on the most comprehensive dataset on Yosemite toad localities available, which was collected by the U.S. Forest Service (USFS) for use in their conservation assessment of the species (as required by the Sierra Nevada Forest Plan Amendment. This data set was compiled by the USFS and comes from various sources, including University of California and California State University researchers, the California Academy of Science, the National Park Service (NPS), the U.S. Geologic Survey, the California Department of Fish and Game (CDFG), and the California Natural Diversity Data Base.

The historic and current acreage of Yosemite toad habitat (wet meadows, shallow breeding waters, and moist uplands) within the historic range of Yosemite toads is unknown, although these habitats have been degraded and may be decreasing in area as a result of conifer encroachment and livestock grazing. The vast majority of land within the range of the Yosemite toad is federally owned, with 649,079 hectares (ha) (1,603,903 ac (ac)) (99 percent of the range) on USFS, National Parks, and Bureau of Land Management lands. Much of this land is within designated wilderness lands. The remaining land within the species' range is a mix of State, local government, and private lands.

It is impossible to fully determine the extent to which Yosemite toads have declined, because baseline data on the number and size of historic populations are few. The following studies reassess the current status of historically documented populations and give the most insight into the species' decline.

Jennings and Hayes reviewed the current status of Yosemite toads using museum records of historic and recent sightings, published data, and unpublished data and field notes from biologists working with the species. They mapped 55 historically documented general localities throughout the range of the species where the toad had been present (based on 144 specific sites), and found that Yosemite toads are now absent from 29 of those localities, a decline of over 50 percent.

In 1990, David Martin surveyed 75 sites throughout the range of the Yosemite toad for which there are historic records of the species' presence, and found that 47 percent of those sites showed no evidence of any life stage of the species (Stebbins and Cohen 1997), a decline of about 63 percent.

Grinnell and Storer surveyed for vertebrates at 40 sites along a 143 km (89 mi) west to east transect across the Sierra Nevada, through Yosemite National Park, in 1915 and 1919. Drost and Fellers conducted more thorough surveys, specifically for amphibians, at 38 of those sites in 1992. They found that Yosemite toads were absent from 6 of 13 sites in which they had been found in the original survey. At sites where Drost and Fellers found Yosemite toads, the toads occurred in low numbers (only 15 total adult and juvenile toads at all sites), with documented declines in relative abundance in three of the Grinnel and Storer sites, as based on their generalized abundance catagories such as rare, common, and abundant. Therefore, the species has declined or disappeared completely from at least 9 of 13 (69 percent) of the Grinnel and Storer (1924) sites.

The only long-term study on the size of a population of Yosemite toads indicates that the population has declined dramatically. Kagarise Sherman and Morton studied Yosemite toads at Tioga Pass Meadow (Mono County, California) intensively from 1971 to 1982, and made less systematic observations from 1983 to 1991. They captured and marked toads entering breeding pools to estimate the adult population size. From 1974 to 1978, an average of 258 males entered the breeding pools. In 1979, the number of male toads began to decline, and by 1982, the number of males had dropped to 28. During the same time period, the number of females varied between 45 and 100, but there was no obvious trend in number observed. In periodic surveys between 1983 and 1991, it appeared that both males and females continued to decline, and breeding activity became sporadic. In 1990, the researchers were only able to locate one female, two males, and four to six egg masses. In 1991, they found only one male and two egg masses. The researchers also surveyed non-breeding habitat in the same area and found similar population declines. To date, the population at Tioga Pass Meadow has not recovered.

Kagarise Sherman and Morton also conducted occasional surveys of six other populations in the eastern Sierra Nevada. Five of these populations showed serious, apparently long-term, declines between 1978 and 1981, while the sixth population held relatively steady until the final survey in 1990, at which time it dropped precipitously. In 1991, E.L. Karlstrom revisited the site at which he had studied a breeding population of Yosemite toads from 1954 to 1958, just south of Tioga Pass Meadow within Yosemite National Park (Tuolumne County, California), and found no evidence of toads or signs of breeding.

Status

On April 3, 2000, the Fish and Wildlife Service received a petition dated February 28, 2000, from the Center for Biological Diversity and Pacific Rivers Council to list the Yosemite toad as endangered. The petitioners also requested that critical habitat be designated concurrent with listing. On December 10, 2002, the Fish and Wildlife Service published a twelve-month petition finding in the Federal Register (Vol. 67, No. 237). The conclusion of the 12-month finding of the U. S. Fish and Wildlife Service is that the proposal to list the Yosemite toad as endangered or threatened is warranted, but is precluded by other higher priority listing actions.

Risk Factors

The U.S. Fish and Wildlife Service's twelve-month petition finding for the Yosemite toad goes into considerable detail citing all relevant research, unpublished data, draft conservation assessment work, and observations by researchers and managers and reveals the potential adverse effects of multiple affectors on the decline of the species and its long-term viability. These multiple affectors may be working singly and in combination at various landscape scales from the local breeding pond to rangewide throughout the Sierra Nevada to decrease the species vigor to withstand population reduction and extirpation events related to disease, weather, and predation.

Potential impacts to this species and its habitat include livestock grazing, commercial and recreational packstock grazing, recreational use of meadows, hiker and stock trails in toad habitat, predation from introduced non-native fish species, forest management herbicide and pesticide applications, pesticide drift from Central Valley agricultural areas, automobile exhaust pollutant drift, disease as a result of fungal, bacterial and other parasitic infections, long-term drought and climate change, and possibly recent increases in UV radiation.

In addition to the risk factors noted in the FEIS (Chap. 3, part 4.4, pg. 218-219), other potential impacts to this species and its habitat include: (1) decreased growth rate of tadpoles as a result of bacterial increase effects from livestock fecal matter, (2) mortality of Yosemite toads from being buried by livestock fecal deposition, (3) reduced vegetative hiding cover for metamorphs, juveniles and adults potentially increasing their vulnerability to predation from snakes, and birds, and (4) the collapse of rodent burrows from livestock hoof punching has the potential to entrap or bury Yosemite toads that use the burrows for hiding cover. The effect on the viability of the Yosemite toad from livestock trampling of toads, cover reduction and subsequent increased predation vulnerability of toads, rodent burrow collapse and toad entrapment and mortality, and adverse effects of livestock and their fecal matter including burying of toads and lower tadpole survival and metamorph growth is unknown. These effects are listed here from researcher unpublished data and personal communications, as well as manager observations and remain to be thoroughly investigated by research.

Research on environmental toxin effects on this species has also not been conducted. The Pacific chorus frog was shown to have lowered levels of Cholinesterase, an important nervous system enzyme, and other amphibians have shown sensitivity to numerous pesticides, herbicides, and fertilizers.

Forest Service management can influence the following affectors: chemical toxins from localized pesticide and herbicide application, livestock grazing, commercial and recreational packstock grazing, recreational use of meadows, hiker and stock trails in toad habitats, fish stocking, and disease spread as a result of Forest Service activities. Forest Service management can also affect genetic diversity of the species, which is important for long-term population viability. Management approaches should aim to maintain all known populations down to specific breeding areas to ensure that genetic diversity is not reduced to the point where the genetic vigor of the species is compromised.

USDA Forest Service · Pacific Southwest Region