Cascade torrent salamander
© 2006 William Flaxington (1 of 17)
Rhyacotriton cascadae Good and Wake, 1992
Marc P. Hayes1
1. Historical versus Current Distribution. Cascade torrent salamanders (Rhyacotriton cascadae) are restricted to the west slope of the Cascades mountain axis from the west bank of the Skookumchuck River in central Washington (0.6 km [0.4 mi] north of the Thurston–Lewis County line; Wilson and Larsen, 1992; McAllister, 1995) south to the Middle Fork of the Willamette River in central western Oregon (Lane County; J. Applegarth, Bureau of Land Management, personal communication; see also Good et al., 1987; Good and Wake, 1992). Cascade torrent salamanders are known to range in elevation to over 1,219 m [4,000 ft], but areal extent of their geographic range is ambiguous largely because upper- and lower-elevation limits, and how these change with latitude, are poorly understood. A watershed-wide study of the Blue River hydrographic basin near the southern end of their geographic range (Willamette River hydrographic basin, Oregon; Hunter, 1998) revealed Cascade torrent salamanders at 52 of 273 (19%) sites, with the probability of occurrence peaking at an elevation of around 870 m (ca. 2,854 ft). Likelihood of occurrence drops markedly above elevations with heavy snow (J. Applegarth, Bureau of Land Management, personal communication), so the latter point may approximate the elevation above which species occurrence begins to decline. The elevation at which heavy snow begins decreases in elevation with increasing latitude, so the upper elevation limit of Cascade torrent salamanders across their geographic range may parallel that pattern. Further, Hunter’s (1998) finding that the maximum size of basins in which Cascade torrent salamanders were detected was 141 ha (348 ac; i.e., relatively small) may indicate the species is infrequent downstream, where gradients are typically lower, thus fewer opportunities exist for appropriate habitat. However, the current distribution pattern may also be influenced by timber harvest, which has been suggested as having a greater influence on lower gradient systems (see “Conservation” below). No attempt has been made to contrast historical versus current distribution. Most data collected on Cascade torrent salamanders are < 30 yr old, so an unambiguous assessment of change may not be possible.
2. Historical versus Current Abundance. No historical abundance data are available, and the few data that provide abundance estimates are relatively recent. Nussbaum and Tait (1977) estimated larval densities of Cascade torrent salamanders at a Columbia River gorge site (Oregon; a small unnamed creek 500 m [ca. 1,640 ft] east of Wahkeena Falls). Density estimates for June–October, which averaged 33.3 larvae/m2 (3.1 larvae/ft2) and ranged from 27.6 larvae/m2 to 41.2 larvae/m2 (2.6 larvae/ft2 to 3.8 larvae/ft2), are among the highest recorded for any species of Rhyacotriton (regardless of sampling method) and are also high in comparison to other salamanders (e.g., Spight, 1967c). Nussbaum and Tait (1977) surmised that the absence of vertebrate competitors and predators at this site at least partly explained the high densities. Nijhuis and Kaplan (1998) estimated adult densities at another Columbia River gorge site (Wahkeena Falls) in March–May 1995, which averaged 1.9 adults/m2 (0.2 adults/ft2; range = 0.3–8.3 adults/m2 [< 0.1–0.8 adults/ft2]). At six sites within both the Mt. Hood National Forest and the Andrews Experimental Forest (Oregon), Bury et al. (1991) reported mean densities of 1.40 individuals/m2 (0.13 individuals /ft2) and 0.07 individuals/m2 (< 0.01 individuals/ft2), respectively.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding migrations have not been documented.
ii. Breeding habitat. Unknown.
i. Egg deposition sites. Nests of Cascade torrent salamanders have not been described. However, nest sites are suspected to have some similarity to those described for the closely related Columbia torrent salamander (R. kezeri; Nussbaum, 1969b; Russell et al., 2002). Columbia torrent salamanders place unattached eggs among the coarse substrate spaces of low-velocity flow seeps.
ii. Clutch sizes. Gravid female Cascade torrent salamanders in the Columbia River gorge averaged 8 ova (range = 2–14; Nussbaum and Tait, 1977).
i. Length of larval stage. Data on Cascade torrent salamanders from the Columbia River gorge indicate a long larval life, estimated between 3–4 yr (Nussbaum and Tait, 1977). This larval interval is long compared with other species of salamanders.
ii. Larval requirements.
a. Food. No data on larval food requirements exist for Cascade torrent salamanders or any other species of Rhyacotriton.
b. Cover. No detailed data exist on cover requirements for Cascade torrent salamander larvae, although Nussbaum and Tait (1977) did comment that Cascade torrent salamander larvae were numerous under stones along a narrow stream channel and in the network of fissures in the streambed and bank. Reporting on pooled data that included some information on Cascade torrent salamanders, Bury et al. (1991) indicated that smaller larvae of Rhyacotriton frequently occurred under small rocks or in beds of gravel, pebbles, and cobbles. Moreover, data from the closely related southern torrent salamander (R. variegatus; Diller and Wallace, 1996; Welsh and Lind, 1996) suggest that stable, slow-flow aquatic microhabitats having unimbedded gravel and cobble (i.e., with open interstices) and reduced levels of fine sediments would be preferred.
iii. Larval polymorphisms. No larval polymorphisms have been described for Cascade torrent salamanders or any other species of Rhyacotriton.
iv. Features of metamorphosis. Metamorphosis of Cascade torrent salamanders in the Columbia River gorge can occur at almost any time, but most individuals appear to metamorphose in late summer to early autumn (Nussbaum and Tait, 1977). The duration of metamorphosis is unknown.
v. Post-metamorphic migrations. Post-metamorphic migrations have not been described for Cascade torrent salamanders or any other species of Rhyacotriton.
vi. Neoteny. Neoteny has not been found in Cascade torrent salamanders (Nussbaum and Tait, 1977), and it is unknown in the genus (Good and Wake, 1992).
D. Juvenile Habitat. Unknown. Based on data for Columbia River gorge Cascade torrent salamanders (Nussbaum and Tait, 1977), little may exist to distinguish the habitat characteristics of juveniles and adults. This comment must be viewed in context of the fact that little effort has been made to distinguish differences in the habitat characteristics of these age groups. Reporting on pooled data that included some information on Cascade torrent salamanders, Bury et al. (1991) found no significant differences either in the shallow water stream depths or use of rocks by different life stages, but this was a post-metamorphic to larval comparison (juveniles were not partitioned from adults in the post-metamorphic category).
E. Adult Habitat. Except for the general comments by Nussbaum and Tait (1977) that, “Favorite hiding places of adults are the underground water-courses in the rock rubble of stream banks, fissures in stream banks, fissures in stream heads and cracks in wet cliff faces,” descriptions of adult habitat are restricted to general accounts (e.g., Leonard et al., 1993; Corkran and Thoms, 1996). Reporting on pooled data that included some information on Cascade torrent salamanders, Bury et al. (1991) noted that Rhyacotriton were most often found in riffles, but life stage data were pooled, so how much of this applies to adults is unclear. A few descriptive data exist for the genus. Stebbins and Lowe (1951) commented that, “The microenvironment of Rhyacotriton … appears uniform throughout … [their geographic] range ….” Detailing the microenvironment, they add, “… characteristically one of a cold, permanent stream with small water-washed or moss-covered rocks (usually rock rubble) in and along … running water … seeps and small, trickling tributary streams with rocks of small dimensions ….” Stebbins and Lowe (1951) also generalized about the vegetation typical of Rhyacotriton-occupied streams, which characterize conditions that provide a cool, wet microenvironment: “Streams harboring Rhyacotriton usually have a good leaf canopy, especially during the summer months … Abundant understory vegetation, much moss, and a thick leaf mat [characterize] stream banks.” They also emphasize the use of rock habitat, stating that Rhyacotriton is “… less frequently found under moss and wood than … rocks.” Emphasizing the wet nature of Rhyacotriton habitat, Stebbins and Lowe (1951) also noted that it was characterized by low flow velocities: “Rhyacotriton usually selects … sites where the movement of water tends to be relatively slow. They rest with their vents in shallow water, and one rarely finds an individual [that is] not in contact with free water or at least a saturated substrate.” This pattern is likely linked to the fact that Rhyacotriton are among the most, if not the most, desiccation intolerant salamander genus known (Ray, 1958). Desiccation intolerance is likely linked to high dependence on skin surfaces for oxygen uptake (average = 74%) because their lungs are highly reduced (Whitford and Hutchison, 1966b). No data on habitat differences between females and males are available for Cascade torrent salamanders or any other species of Rhyacotriton.
F. Home Range Size. Few data are available on home range size per se for Cascade torrent salamanders. Available data suggest that Cascade torrent salamanders are sedentary (Nussbaum and Tait, 1977; Nijhius and Kaplan, 1998), with movements on the scale of a few meters being typical. Using 2-m stream edge increments to distinguish movement, Nussbaum and Tait (1977) found that 134 of 191 (70%) recaptured Cascade torrent salamander larvae made no net movement (i.e., recaptured in the same 2-m interval). Thirty-nine (20%) revealed net movement upstream, and the other 18 (10%) showed net movement downstream, a significant difference. The greatest distance moved, 22 m, was displayed by two larvae, one that moved upstream and the other downstream. Using range length (the distance between the two most widely separated points of capture), Nijhuis and Kaplan (1998) found mean range length for Cascade torrent salamander adults captured at least three times during the spring at a Columbia River gorge site was 2.4 m (7.9 ft; range = 0.2–6.0 m [0.7–19.7 ft]). Nijhuis and Kaplan (1998) also used the relatively high percentage of individuals recaptured (36%) in a small portion of available habitat studied to indicate the high degree of sedentation. Further, they found no differences in the magnitude of movements between the age, sex, or size groupings of post-metamorphic Cascade torrent salamanders examined. While the sedentary pattern in these reports is probably real, these data must be interpreted with the knowledge that each of these studies suffers from some degree of bias because recaptures with the intent of identifying movements were made exclusively within highly circumscribed, small areas.
G. Territories. No data are available on territoriality. Available data on Cascade torrent salamanders indicate high densities and restricted movements (Nussbaum and Tait, 1977; Nijhius and Kaplan, 1998; see "Current versus Historical Abundance" and "Home Range Size" above), implying territorial behavior to be unlikely. However, the behavioral data needed to interpret territorial defense are lacking.
H. Aestivation/Avoiding Dessication. Unknown.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. In the Columbia River gorge (Oregon; Nussbaum and Tait, 1977; Nijhius and Kaplan, 1998; personal observations) and probably elsewhere within their range, Cascade torrent salamanders display at least some degree of syntopy with five different amphibian species: coastal tailed frogs (Ascaphus truei), Cope's giant salamanders (Dicamptodon copei), coastal giant salamanders (D. tenebrosus), western red-backed salamanders (P. vehiculum), and Dunn's salamanders (P. dunni). Patterns of syntopy with each of these taxa have not yet been detailed. Based on studies of other Rhyacotriton, giant salamanders are repeatedly mentioned as potential predators that could locally limit Rhyacotriton (Stebbins, 1953; Welsh, 1993; Welsh and Lind, 1996). Inverse relationships in abundance between torrent and giant salamander larvae (Welsh and Lind, 1996) and anecdotal observations regarding the relative rarity of syntopy between torrent and giant salamanders (Stebbins, 1953) seem to be the basis of these comments. Recent work revealing that larval southern torrent salamanders are unpalatable to larval coastal giant salamanders (Rundio and Olson, 2001) suggests that the role giant salamanders play in limiting torrent salamanders requires re-evaluation or more thorough investigation. At least one species of Rhyacotriton (e.g., southern torrent salamander) is known to move away from injured western red-backed salamanders (Chivers et al., 1997), apparently as a predator avoidance response. Cascade torrent salamanders may show a similar pattern.
L. Age/Size at Reproductive Maturity. Nussbaum and Tait (1977) estimated that Columbia River Gorge Cascade torrent salamanders require 5.5–6.0 yr to reach reproductive maturity at a minimum size of 41 mm SVL for males, 44 mm for females.
M. Longevity. Unknown. Nussbaum and Tait (1977) imply that a moderately long lifespan (≥ 10 yr) is likely.
N. Feeding Behavior. Unknown. Based on data for other Rhyacotriton, Cascade torrent salamanders probably feed in moist forested habitats on invertebrates, notably amphipods, fly larvae, springtails, and stonefly nymphs (Bury and Martin, 1967; Bury, 1970). These taxa occur in the semi-aquatic and aquatic microhabitats where feeding is thought to occur.
O. Predators. No predators of Cascade torrent salamanders have been recorded. Based on studies of other Rhyacotriton, giant salamanders are suspected predators (Stebbins, 1953; Nussbaum, 1969b; Welsh, 1993; Welsh and Lind, 1996), but the recent demonstration of the relative unpalatability of southern torrent salamander larvae (Rundio and Olson, 2001) may require re-evaluation of which torrent salamander life stages may be vulnerable to giant salamander predation. Nussbaum et al. (1983) also commented on shrews (Soricidae) rejecting torrent salamanders as unpalatable.
P. Anti-Predator Mechanisms. No anti-predator mechanisms have been recorded for Cascade torrent salamanders. Brodie (1977) described anti-predator postures in Olympic torrent salamanders (R. olympicus sensu lato) as similar to many Ambystoma. The body is coiled, and the tail is elevated or arched and wagged and may be lashed toward a threat. The bright yellow venter contrasting with the drabber dorsal coloration is believed to be aposematic. Partly metamorphosed larvae postured similarly to adults. The recent demonstration that southern torrent salamander larvae are unpalatable (see “Interspecific Associations/Exclusions” above) may agree with an aposematic hypothesis, but unpalatability of post-metamorphic life stages remains to be demonstrated. Based on an experimental study of southern torrent salamanders, avoidance of injured conspecifics and injured western red-backed salamanders (Chivers et al., 1997) may be an anti-predator device also present in Cascade torrent salamanders.
Q. Diseases. Not examined.
R. Parasites. One species of monogenoidean fluke, to date unique to Rhyacotriton (Kristsky et al., 1993), has been recorded from Cascade torrent salamanders. However, several other species of digenean flukes (Lynch, 1936; Senger and Macy, 1952; Lehman, 1954; Anderson et al., 1966; Martin, 1966b) and blood parasites (Clark et al. 1969) have been described from other species of Rhyacotriton and may occur in Cascade torrent salamanders.
4. Conservation. Cascade torrent salamanders have state Sensitive status in both the states that encompass their geographic range: Oregon (Marshall et al., 1996) and Washington (K. McAllister, personal communication). In both states, "Sensitive" consists of a watchlist status that lacks legal standing, but it is applied to species for which serious concerns exist related to habitat loss in order to increase awareness among resource protection agencies. In the case of both states, Sensitive status was established because concern existed that the rapid rate of conversion of mature and old-growth forests to young stands as a function of timber harvest were limiting habitat quality through increased microhabitat temperatures and sedimentation, and that local extirpation was resulting from these changes (Corn and Bury, 1989a). Concern also existed that headwater streams, seeps, and springs (all habitats presumed to be occupied) lacked adequate protection. Data used to support sensitive status were an amalgam of information drawn entirely from retrospective studies that addressed related southern torrent salamanders (e.g., Corn and Bury, 1989a; Welsh, 1990, 1993; Welsh and Lind, 1996).
The actual status of Cascade torrent salamander is unstudied. Lower-gradient, higher-order streams, which may intrinsically provide poor habitat for Rhyacotriton (see “Historical versus Current Distribution” above) are often more disturbed as a function of timber harvest (due to greater susceptibility to habitat disturbance because of greater depositional and more limited scour characteristics, a greater upslope area of influence, more harvest rotations, etc.) than higher- gradient, lower-order streams, which may provide better habitat (Diller and Wallace, 1996; Welsh and Lind, 1996; Hunter, 1998). A recent retrospective study of Cascade torrent salamanders focusing on headwater landscapes with stands harvested 0–60 yr ago revealed the highest densities of torrent salamanders associated with stands 21–40 yr old (Steele, 2001). Unfortunately, too few unharvested stands with parallel site criteria were available for comparison. Distinguishing the relative significance of intrinsic habitat limitation from the potential influences of timber harvest will require comparing harvested and unharvested lower- versus higher-gradient sites simultaneously.
In 2000, scientists representing private timber companies, Native American tribes, and state and federal resource agencies assessed the risk of forest management activities to stream-associated vertebrate species. This work, done in preparation to the Washington Forest and Fish Agreement (FFA), concluded that seven species of amphibians (including all three species of torrent salamanders in Washington State) were at high risk of local extirpation from forest management. One outcome of identifying species at risk and including them in the list of species protected under new forest practice rules was that those species would be studied as part of an innovative, ambitious adaptive management program. The goal of FFA adaptive management is to determine whether new riparian buffer prescriptions designed for headwater streams are effective in protecting resources to which they are linked, including local populations of Rhyacotriton. To date, this research has identified the most appropriate sampling methods for landscape detection and relative abundance assessment of Cascade torrent salamanders and the other stream-associated amphibians. These methods will be essential for manipulative studies to test the effectiveness of forest practice rules in protecting Rhyacotriton.
1Marc P. Hayes
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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