Columbia torrent salamander
© 2006 William Flaxington (1 of 19)
Rhyacotriton kezeri Good and Wake, 1992
Marc P. Hayes1
1. Historical versus Current Distribution. Columbia torrent salamanders (Rhyacotriton kezeri) are restricted to coastal and near-coastal regions of northwestern Oregon and southwestern Washington, from the Little Nestucca River system (Tillamook County, Oregon) in the south to the Chehalis River (Gray’s Harbor County, Washington) in the north (Good and Wake, 1992; McAllister, 1995). Across this range, Columbia torrent salamanders occur from near sea level to the highest elevations in the region (i.e., Boisfort Peak, 948 m [3,110 ft], in the Willapa Hills of southwestern Washington, and Saddleback Mountain, 1,001 m [3,283 ft], in the coast ranges of northwestern Oregon). They occur in some upper reaches of the coastal part of the Willamette hydrographic basin (e.g., Upper Grand Ronde system, Oregon [see Good et al., 1987]). However, their distribution across the region and their inland distribution in parts of Washington (especially in the Willapa Hills State Forest area; see McAllister, 1995) are poorly known. In the Willapa Hills, Columbia torrent salamanders were encountered in 53% of 40 near-coastal perennial headwater streams in a managed forest landscape (Wilkins and Peterson, 2000). Wilkins and Peterson (2000) also found that likelihood of occupancy for Columbia torrent salamanders generally increased as channel gradient increased and basin area decreased, so that the likelihood of occupancy generally increased as one moved toward headwaters. Farther inland in the Willapa Hills, Columbia torrent salamanders were detected in 73% of 70 headwater streams in managed forests (D. Runde, personal communication). A recent study of a large segment of Oregon Columbia torrent salamander range revealed them to be widespread in headwater streams of managed forests (occurring in 58% of such randomly selected streams); this study also showed that Columbia torrent salamanders occurred more often in streams on basalt formations than in streams on marine sediments (Russell et al., in press). These authors also found that streams with northerly aspects were significantly more likely to have Columbia torrent salamanders than streams with southerly aspects. In a study in the Kilchis River drainage (Oregon), Columbia torrent salamanders were observed at 67% of 33 sites (D. Vesely, Pacific Northwest Research Institute, personal communication). No attempts have been made to contrast historical with current distribution, but the study by Russell et al. (in press), which was conducted over a large segment of the historic Tillamook burn, suggested that this species may be resilient to habitat-altering catastrophic disturbance (at least for this high precipitation coastal area). The Tillamook burn consisted of a series of stand-replacing events that occurred over an 18-yr period (1933-'51) and covered over 121,000 ha (300,000 ac). Still, most data on Columbia torrent salamanders are < 30 yr old, so that a range-wide historical assessment may not be possible.
2. Historical versus Current Abundance. No historical data on abundance are available, but some recent studies provide relative abundance data. In the Willapa Hills, Columbia torrent salamanders made up 21% of the individuals across eight amphibian species and ranked second only to giant salamanders (Dicamptodon sp.) in relative abundance (Wilkins and Peterson, 2000). In two other unpublished studies conducted in the Willapa Hills, Columbia torrent salamanders ranked first in abundance among the 9 (D. Runde, Weyerhaeuser Company, personal communication) and 13 (unpublished data) amphibian species recorded; in both cases they represented > 60% of individuals of all species. In the Russell et al. (in press) study, Columbia torrent salamander densities ranged from 0–68.3 individuals/m2; the upper end is the highest recorded for any torrent salamander species. Relative abundance of Columbia torrent salamanders is not always among the highest in amphibian assemblages. In a Kilchis River study, Columbia torrent salamanders ranked fourth in relative abundance among the ten amphibian species recorded (D. Vesely, personal communication). At least part of the reason for this disparity in relative abundance patterns across studies may depend upon how sampling locations were selected within hydrographic basins, as Russell et al. (in press) indicated that Columbia torrent salamander density increases with proximity to the headwater channel origin.
Two of the three studies in the Willapa Hills found some degree of inverse relationship between relative abundance and gradient. Because these studies were all conducted in landscapes managed for timber harvest, these data are difficult to interpret. The notion that low gradients may intrinsically provide less opportunity for favorable habitat is confounded with the potential for these low-gradient habitats to have been most heavily influenced by timber harvest (see “Conservation” below). Russell et al. (in press) also found that relative abundance of Columbia torrent salamanders was significantly greater in streams with basalt substrates than in streams with marine sedimentary substrates, a finding consistent with Columbia torrent salamander occupancy patterns (Wilkins and Peterson, 2000; see “Historical versus Current Distribution” above). Through the generation of a coarser-grained substrate structure, balsalt substrates are thought to provide more suitable habitat than sedimentary substrates (Wilkins and Peterson, 2000), but competence of the substrate, rather than the formation per se, may be the important factor in habitat quality, all else being equal (see Dupuis et al., 2000). Excessive inputs of fine substrates has been often-suggested as a factor degrading habitat quality for stream-associated amphibians such as Columbia torrent salamanders (e.g., Corn and Bury, 1989a; Welsh and Lind, 1996; Dupuis et al., 2000).
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Breeding migrations have not been documented for this species.
ii. Breeding habitats. Unknown.
i. Egg deposition sites. Nussbaum (1969b) described two nest sites attributable to Columbia torrent salamanders (the species was not described until Good and Wake ), and more recently, Russell et al. (2002) described three more nests. Four of the nests were from Oregon, the remaining one was from Washington. One of the Nussbaum nests, discovered on 14 December, was found during the excavation of a headwater spring. The other nest Nussbaum described, found on 28 September in a side-slope seep, was revealed by prying loose a large (2.4 m x 1.2 m x 1.2 m [8 ft x 4 ft x 4 ft]) rock block that root action in a seep had separated from the base of a cliff. Both nest sites were in sandstone; had relatively cold (8.3–9.0 ˚C), slow-flowing water trickling over loose, unattached eggs; had more eggs (16–75) than could have been laid by one female; and lacked an attendant adult (several adults and one larvae were within 60 cm [2 ft] of the 14 December nest, but none were near the eggs, whereas only three young larvae were seen near the 28 September nest [Nussbaum 1969b]). Embryos in both nests were in tail-bud stage. Based on these observations, Nussbaum (1969b, 1985) concluded that eggs are not attached to substrate (a condition unique in salamanders), no parental care exists, and communal oviposition may be typical.
The three nests Russell et al. (2002) found broadened the knowledge of nest site variation, as two were from springs at the origin of first-order streams and the third was in a first-order channel, 75 m downstream of the origin. One of the nests found in a spring was under a small boulder (33 cm x 20 cm x 10 cm) underlain by fine sediments and sand, whereas the other two nests were under thick layers of moss (17 cm in the one nest measured) on substrates consisting of a mix of gravels and fine organic sediments. In all three cases, the lithology was an unspecified marine sedimentary formation. Unlike the nests Nussbaum (1969b) described, these nests were discovered between 16–26 July, and the eggs had no evidence of embryological development. Mean egg size from the three Russell et al. (in press) nests ranged from 3.8–4.1 mm in diameter exclusive of jelly capsules; egg diameter data were not obtained from the nests Nussbaum (1969b) described. Further, Russell et al. (2002) reported 1–2 adult female Columbia torrent salamanders in the vicinity of two of the three nests; a distance between adults and eggs was specified only for the two-female nest, in which case both females were within 5 cm of the eggs. Russell et al. (2002) agreed with most interpretations of Nussbaum (1969b, 1985), but considered the question of parental care open. Further, the number of eggs in the nests Russell et al. (2002) described, 7–11, may each represent a single clutch. Overall, these observations suggest that oviposition may be restricted to low-flow headwater habitats, probably because unattached eggs would be at risk from scour at higher flows. That few nest sites that have been found suggests that placement of eggs typically occurs in relatively inaccessible, cryptic locations.
ii. Clutch size. Unknown. If eggs from the Russell et al. (2002) nest descriptions represent single clutches, and no eggs were lost prior to their discovery, clutch size may be 7–11. Based on data for other species of Rhyacotriton (Nussbaum and Tait, 1977), fecundity is likely to be low (2–16 eggs).
i. Length of larval stage. Except for the egg stage, no life history data exist for Columbia torrent salamanders. However, data from closely related species of Rhyacotriton (Nussbaum and Tait, 1977) suggest that Columbia torrent salamanders probably remain larvae for a relatively long period (> 2 yr).
ii. Larval requirements.
a. Food. Unknown.
b. Cover. Unknown. Habitat data from Russell et al. (in press) were not partitioned by life stages. However, Columbia torrent salamander larvae represented 60% of the individuals encountered in surveys, and habitat data generally agree with larval data from closely related species of Rhyacotriton (Nussbaum and Tait, 1977; Diller and Wallace, 1996; Welsh and Lind, 1996), suggesting that stable, slow-flow stream microhabitats with loose gravel and cobble, open interstices, and reduced levels of fine sediments are preferred.
iii. Larval polymorphisms. Have not been described and are unlikely.
iv. Features of metamorphosis. Unknown. Data from closely related species of Rhyacotriton indicate that metamorphosis can occur at almost any time, but a majority of individuals appear to metamorphose in late summer to early autumn (Nussbaum and Tait, 1977). The duration of metamorphosis is unknown.
v. Post-metamorphic migrations. Have not been described and are unlikely.
vi. Neoteny. Unknown in the genus Rhyacotriton (Good and Wake, 1992).
D. Juvenile Habitat. Unknown. Based on related species of Rhyacotriton (Nussbaum and Tait, 1997), few data exist to suggest that habitat requirement of adults and juveniles differ. However, almost no effort has been made to distinguish partitioning the habitat requirements of these age groups.
E. Adult Habitat. Except for nest-site habitat characterized by Nussbaum (1969b) and Russell et al. (2002), descriptions of Columbia torrent salamander habitat are limited to landscape and reach scale elements that Russell et al. (in press) discussed (see “Historical versus Current Distribution” and “Historical versus Current Abundance” above). However, some descriptive data encompass the genus. Stebbins and Lowe (1951) stated that “The microenvironment of Rhyacotriton appears uniform throughout…[their geographic] range ….” On 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 are sites [where] numbers of these salamanders may be found.” Stebbins and Lowe (1951) also generalized about the vegetation typical of streams where Rhyacotriton are found 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.” Emphasizing the use of rock habitat, Stebbins and Lowe (1951) noted that Rhyacotriton are “… less frequently found under moss and wood than … rocks.” In 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 genera known (Ray, 1958). This intolerance is probably linked to a high dependence on skin surfaces for oxygen uptake (on average 74% of uptake is through the skin) because the lungs are highly reduced (Whitford and Hutchison, 1966b). No data on habitat differences between females and males are available for Columbia torrent salamanders or any other species of Rhyacotriton.
F. Home Range Size. Unknown. Data from other species of Rhyacotriton suggest that individuals are highly sedentary (Nussbaum and Tait, 1977, Welsh and Lind, 1992; Nijhius and Kaplan, 1998), with movements typically limited to a few meters. A highly sedentary pattern may be characteristic of the genus. Yet, all movement studies to date suffer from some degree of bias because recaptures with the intent of delineating home ranges were limited to highly circumscribed, small areas. The latter limitation is likely a function of the high cost associated with thorough searches.
G. Territories. Unknown. Available data on closely related Cascade torrent salamanders (Rhyacotriton cascadae) indicate high densities and restricted movements (Nussbaum and Tait, 1977; Nijhius and Kaplan, 1998), implying territorial behavior is unlikely. However, these indirect data must be viewed cautiously because data on behaviors related to territorial defense are lacking.
H. Aestivation/Avoiding Dessication. Unknown. However, surface activity may be reduced during late summer to early autumn (personal observations), when surface conditions are driest.
I. Seasonal Migrations. Unknown. Different studies on other species of Rhyacotriton appear to suggest conflicting patterns (upstream versus downstream) in larval movements (see Nussbaum and Tait, 1977; Welsh and Lind, 1992) that will require more study for correct interpretation.
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Over their range, Columbia torrent salamanders are sympatric with 12 different amphibian species: northwestern salamanders (Ambystoma gracile), long-toed salamanders (A. macrodactylum), Cope's giant salamanders (Dicamptodon copei), coastal giant salamanders (D. tenebrosus), rough-skinned newts (Taricha granulosa), ensatinas (Ensatina eschscholtzii), Van Dyke's salamanders (Plethodon vandykei), western red-backed salamanders (P. vehiculum), Dunn's salamanders (P. dunni), coastal (Pacific) tailed frogs (Ascaphus truei), Pacific treefrogs (Pseudacris regilla), and northern red-legged frogs (Rana aurora; McAllister, 1995; Vesely, 1997; D. Vesely, Pacific Northwest Research Institute; D. Runde, Weyerhaeuser Company, personal communication). However, degree of syntopy with each of these taxa has 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 salamanders [R. variegatus]) is known to move away from injured western red-backed salamanders (Chivers et al., 1997) apparently as a predator avoidance response; Columbia torrent salamanders may show a similar response.
L. Age/Size at Reproductive Maturity. Unknown. Based on data for other Rhyacotriton (Nussbaum and Tait, 1977), Columbia torrent salamanders probably have a relatively long interval to reproductive maturity (4 yr) and a relatively small size at reproductive maturity (about 45 mm SVL).
M. Longevity. Unknown. Based on data for other Rhyacotriton (Nussbaum and Tait, 1977), a moderately long lifespan (> 10 yr) is likely.
N. Feeding Behavior. Unknown. Based on data for other Rhyacotriton, Columbia torrent salamanders probably feed on invertebrates dwelling in moist forested habitats, especially amphipods, fly larvae, springtails, and stonefly nymphs (Bury and Martin, 1967; Bury, 1970). These taxa occur in semi-aquatic and aquatic microhabitats where feeding is thought to occur.
O. Predators. Unknown. Based on studies of other Rhyacotriton, giant salamanders are suspected predators (Stebbins, 1953; Nussbaum, 1969b; Welsh, 1993; Welsh and Lind, 1996). However, the recent demonstration of the relative unpalatability of southern torrent salamander larvae to giant salamanders (Rundio and Olson, 2001) suggests that more study is needed to determine 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. Unknown. Brodie (1977) described anti-predator postures in Olympic torrent salamanders (R. olympicus) sensu lato as similar to many mole salamanders (Ambystoma sp.). 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 posture similarly to adults. The recent demonstration that southern torrent salamander larvae are unpalatable (see “Interspecific Associations/Exclusions” above) may help support the 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 behavior also present in Columbia torrent salamanders.
Q. Diseases. No diseases have been recorded.
R. Parasites. Unknown. However, several species of parasites have been described from other species of Rhyacotriton, and may occur in Columbia torrent salamanders. These include one species of monogenoidean fluke, to date unique to Rhyacotriton (Kristsky et al., 1993), and several 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).
4. Conservation. Columbia 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 there is concern related to habitat loss in order to increase awareness among resource protection agencies. In the case of both states, Sensitive status was established because > 97% of the species range was located in young stands (< 80 yr old) intensively managed for timber. Much concern for Columbia torrent salamanders was related to the idea that habitat quality would be degraded by increased temperatures and sedimentation following timber harvest. Concern also existed that headwater streams, seeps, and springs (all habitats presumed to be occupied) lacked adequate protection. Data used to support the Sensitive designations were drawn entirely from retrospective studies that addressed the southern torrent salamander (e.g., Corn and Bury, 1989a; Welsh, 1990).
The actual status of Columbia torrent salamanders 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. Thus, the effect of timber harvest per se on torrent salamanders has been confounded with natural variation in habitat quality (Diller and Wallace, 1996; Welsh and Lind, 1996; Hunter, 1998). Unfortunately, historical harvest patterns have made it difficult to find unharvested stands in low-gradient streams that could serve as experimental units. 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. Using surveys conducted on 20 x 40 m plots, Vesely and McComb (2002) showed that torrent salamanders were sensitive to forest practices in riparian areas, and that riparian buffer strips ca. 43 m wide would support a total salamander abundance (including torrent salamanders) similar to that in unlogged forests. Unfortunately, low numbers of torrent salamanders forced Vesely and McComb (2002) to pool the data for Columbia and southern torrent salamanders, making it impossible to determine the response of Columbia torrent salamanders alone.
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 Columbia 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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