Olympic Torrent Salamander
© 2010 Michael Graziano (1 of 16)
Rhyacotriton olympicus (Gaige, 1917)
Marc P. Hayes1
1. Historical versus Current Distribution. Olympic torrent salamanders (Rhyacotriton olympicus) are restricted to the region of the Olympic Peninsula (i.e., south to the Chehalis River) in Washington state (Good and Wake, 1992; McAllister, 1995). A notable hiatus is the lack of records for this species in the Black Hills complex near the immediate southern margin of Puget Sound, but north of the Chehalis River (McAllister, 1995), which may reflect the southernmost advance of the last glaciation, which just covered this complex. Limited historical data exist for this species (Slater, 1933, 1955), but no attempts have been made to contrast historical and current distribution. Most data on Olympic torrent salamanders are relatively recent, so only a limited historical assessment may be possible. Recent surveys of Olympic National Park (Bury and Adams, 2000) showed the species to be widespread, occurring in 41% of 168 streams and 47% of 235 seeps surveyed. Few locations were found on the east side of the Park, where conditions are drier and warmer due to the rain shadow of the Olympic Mountains (see also “Conservation” below).
2. Historical versus Current Abundance. Recent survey of Olympic National Park (Bury and Adams, 2000) revealed that Olympic torrent salamanders were more abundant in streams with northerly aspects and steep gradients. The latter is a pattern that has been identified in every species of Rhyacotriton where it has been studied (e.g., Welsh and Lind, 1996; Russell et al., in press) and may reflect a process-based greater facility for maintaining suitable habitat in such systems. Although associations with steeper gradients could be confounded with influences from timber harvest that may operate differently under different gradient conditions (see “Conservation” below), such a confound is unlikely for Bury and Adams’ (2000) Olympic National Park surveys, because timber harvest has never occurred over most of the area they surveyed. Bury and Adams (2000) also found Olympic torrent salamanders to be less abundant where fine substrates and undercut banks were more frequent. No historic abundance data exist, and future contrasts of potential changes in abundance will either require comparison to Bury and Adams (2000) or establishment of their own baseline for contrast.
3. Life History Features.
A. Breeding. Reproduction is presumed to be aquatic (see "Egg deposition sites" below).
i. Breeding migrations. Breeding migrations are undocumented.
ii. Breeding habitat. Unknown.
i. Egg deposition sites. No egg deposition sites of this species have been described. Five nests of Columbia torrent salamanders (R. kezeri) are known from seeps, springs, or headwater streams with mixed (coarse and fine) substrates; sometimes nests are beneath a layer of moss (Nussbaum, 1969b; Russell et al., 2002). One nest of southern torrent salamanders (R. variegatus) was found in the mid channel of a small, headwater stream (Karraker, 1999). From these observations, low-flow egg deposition sites with similar characteristics are anticipated for Olympic torrent salamanders.
ii. Clutch size. Unknown, but fecundity is likely to be low because Good and Wake (1992) indicated that gravid female Olympic torrent salamanders have ovarian egg counts averaging eight.
i. Length of larval stage. Unknown. However, data from Cascade torrent salamanders (R cascadae) and southern torrent salamanders (Nussbaum and Tait, 1977) suggest that Olympic torrent salamanders probably have a long larval life (> 2 yr).
ii. Larval requirements.
a. Food. Unknown.
b. Cover. Unknown. However, data from other species of Rhyacotriton (Nussbaum and Tait, 1977; Diller and Wallace, 1996; Welsh and Lind, 1996) suggest that stable, low-flow volume microhabitats with loose gravel and cobble and open interstices with limited fine sediments may be preferred.
iii. Larval polymorphisms. Unknown for any species of Rhyacotriton.
iv. Features of metamorphosis. Unknown. Nussbaum and Tait (1977) indicated that Cascade torrent salamanders and southern torrent salamanders can metamorphose at almost any time of the year, but their data indicate most individuals metamorphose in late summer to early autumn. The duration of metamorphosis is unknown.
v. Post-metamorphic migrations. Have not been described for any species of Rhyacotriton.
vi. Neoteny. Unknown in the genus Rhyacotriton (Good and Wake, 1992).
D. Juvenile Habitat. No data exist on juvenile habitat characteristics. Based on data for related species of Rhyacotriton (Nussbaum and Tait, 1977), few differences appear to exist between the habitat characteristics of juveniles and adults. However, almost no effort has been made to distinguish habitat partitioning by these age groups.
E. Adult Habitat. Except for the recent habitat analysis of Bury and Adams (2000; see “Current and Historic Distribution” and “Current and Historic Abundance” above), available descriptions of habitat for Olympic torrent salamanders are limited. Leonard et al. (1993) state that “R. olympicus are nearly always seen in or very near cold, clear streams, seepages, or waterfalls. Their typical haunt is the splash zone, where a thin film of water runs between or under rocks.” Descriptions encompassing the genus add some additional data. Emphasizing the use of rock habitats, 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, they also noted that: “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 is among the most, if not the most, desiccation intolerant salamander genus known (Ray, 1958). Desiccation intolerance is probably linked to a high dependence on skin surfaces for oxygen uptake (average = 74%) because the lungs are highly reduced (Whitford and Hutchison, 1966b). Stebbins and Lowe (1951) also generalized about vegetation typical of streams where Rhyacotriton are found. These streams are characteristic of conditions that provide a cool, wet microenvironment: “Streams harboring Rhyacotriton usually have a good leaf canopy, especially during the summer … Abundant understory vegetation, much moss, and a thick leaf mat [characterize] stream banks.”
F. Home Range Size. Unknown. Data from other species of Rhyacotriton suggest that the range of movement of individuals is limited (i.e., on a few-meter scale; Nussbaum and Tait, 1977; Welsh and Lind, 1992; Nijhius and Kaplan, 1998). An interpretation of limited movement must be given with the caveat that all studies to date suffer from some degree of bias because recaptures with the intent of identifying movements in a home range context were within highly circumscribed, small areas.
G. Territories. Unknown.
H. Aestivation/Avoiding Dessication. Olympic torrent salamanders have been encountered when surface active during the summer (Jones and Raphael, 2000), so aestivation may not be typical or necessary in their highly mesic, near hydric habitats.
I. Seasonal Migrations. Unknown.
J. Torpor (Hibernation). Unknown.
K. Interspecific Associations/Exclusions. Olympic torrent salamanders are often associated with coastal tailed frogs (Ascaphus truei), Cope's giant salamanders (Dicamptodon copei), Van Dyke's salamanders (Plethodon vandykei), and western red-backed salamanders (P. vehiculum) in seep and stream habitats (L. Jones, unpublished data; P. Peterson, Simpson Timber Company, personal communication). However, the degree of syntopy with each of these taxa has not yet been detailed. Based on studies of other Rhyacotriton, a repeated comment has been that giant salamanders, as potential predators, 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) will require re-evaluation of the notion of just how giant salamander predation may limit torrent salamanders. At least one species of Rhyacotriton (e.g., southern torrent salamander) is known to respond to stimuli from injured western red-backed salamanders (Chivers et al., 1997); a similar pattern may be true for Olympic torrent salamanders.
L. Age/Size at Reproductive Maturity. Unknown. Based on data for other Rhyacotriton (Nussbaum and Tait, 1977), a relatively long interval to reproductive maturity (> 4 yr) and a relatively small size at reproductive maturity (about 45 mm SVL) are anticipated.
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, Olympic torrent salamanders probably feed on invertebrates dwelling in moist forested habitats, especially amphipods, dipteran 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. Unknown. 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 rejecting torrent salamanders as unpalatable.
P. Anti-Predator Mechanisms. Unknown. Brodie (1977) described anti-predator postures in Rhyacotriton as being similar to many Ambystoma. In defense, the body is coiled, and the tail is elevated or arched and wagged and may be lashed toward the 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 agree with an aposematic hypothesis, but unpalatability of post-metamorphic life stages remains to be demonstrated. Based on 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 Olympic torrent salamanders.
Q. Diseases. Unknown.
R. Parasites. Unknown. However, several species of parasites have been described from other species of Rhyacotriton and may occur in Olympic torrent salamanders. These include one species of monogenoidean fluke, to date unique to Rhyacotriton (Kristsky et al., 1993), several species of digenean flukes (Lynch, 1936; Senger and Macy, 1952; Lehmann, 1954, 1956; Anderson et al., 1966; Martin, 1966b), and several blood parasites (Clark et al., 1969).
4. Conservation. Olympic torrent salamanders are state Sensitive in Washington (K. McAllister, personal communication). "Sensitive" is a watchlist status that lacks legal standing, but it is applied to species for which concern exists related to habitat loss in order to increase awareness among resource protection agencies. Much concern for the species 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 status were drawn entirely from retrospective studies that addressed southern torrent salamanders (e.g., Corn and Bury, 1989a; Welsh, 1990).
The actual status of Olympic torrent salamanders is unstudied. Lower-gradient, higher-order streams, which may intrinsically provide poor habitat for Rhyacotriton (see “Historical versus Current Distribution” above), are more often 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 quality. Thus, the effects of timber harvest per se on torrent salamanders have been confounded with natural variation in habitat quality (Diller and Wallace, 1996; Welsh and Lind, 1996; Hunter, 1998). However, based on Bury and Adams (2000), little question exists that gradient has an influence on habitat in its own right; what is unclear is how much degradation may have occurred in lowland habitats where gradients are lower and the influence of timber harvest is extensive. 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 salamander 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 Olympic 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
2Lawrence L.C. Jones
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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