Southern Torrent Salamander
© 2006 William Flaxington (1 of 64)
Rhyacotriton variegatus Stebbins and Lowe, 1951
Hartwell H. Welsh Jr.1
1. Historical versus Current Distribution. Southern torrent salamanders (Rhyacotriton variegatus) are locally distributed in the Pacific Coast ranges of Oregon from the Little Nestucca River southward to Dark Gulch in Mendocino County, California (Good and Wake, 1992; but see Highton, 2000, who suggests that there may be four cryptic species composing a R. variegatus species group). Apparently disjunct populations of Rhyacotriton in the north Umpqua River drainage of the interior southern Cascade Mountains of Oregon are attributed to southern torrent salamanders (Good and Wake, 1992). However, recent sampling between the Umpqua drainage and the coast ranges of southern Oregon indicates extant populations of southern torrent salamanders occur across this geography (R. Bury, personal communication). There are five specimens known from a disjunct locality about 113 km (70 mi) east of the established range (Stebbins, 1985) in the upper McCloud River drainage in Siskiyou County, California (Jennings and Hayes, 1994a). The distribution of populations within the range of southern torrent salamanders is generally spotty, with occurrences closely linked to headwater habitats. Based on two studies in northern California, Welsh and Lind (1992) found southern torrent salamanders present at 28% and 37%, respectively, of aquatic sites randomly sampled across the range. They found that presence of headwater habitat alone was not a good predictor of salamander presence; only 62.3% and 46.6%, respectively, of sites sampled with headwater microhabitats supported salamanders (Welsh and Lind, 1992). Welsh (1990) reported southern torrent salamanders associated with headwater habitats in late seral forests throughout much of their range in California (see also Welsh and Lind, 1988, 1991, 1996). However, Diller and Wallace (1996) reported no relationship between the presence of southern torrent salamanders and seral stage on coastal redwood commercial timberlands. Possible bioregional differences aside, numerous studies have shown that southern torrent salamanders are negatively impacted by timber harvesting (Corn and Bury, 1989a; Welsh, 1990; Bury et al., 1991; Welsh and Lind, 1996; Welsh et al., 1998; Welsh et al., in preparation), and thus indicate that their historical distribution may have consisted of more populations across the range than is currently the case. For example, Welsh et al. (1998) reported that southern torrent salamander populations occurred in only 29.0% of headwater habitats in the heavily logged Mattole watershed of southern Humboldt County, California, and 18.9% of headwater habitats on commercial timberlands just to the south in Mendocino County. Both rates of occurrence were significantly lower than the 62.3% and 46.6% random encounter rates reported above (see Welsh and Lind, 1992), or the 76.9% encounter rate found on proximate forest reserve lands in northern Mendocino County. Few studies that directly address this question are available from the Oregon portions of the range (but see Corn and Bury, 1989a). However, a similar trend of region-wide intensive, short-rotation forestry throughout the Oregon Coast ranges has probably severely reduced populations there as well.
2. Historical versus Current Abundance. Historical abundances are unknown; however, evidence from multiple studies on the impacts of timber harvesting (e.g., Corn and Bury, 1989a; Welsh, 1990; Welsh et al., 2000; Welsh et al., in preparation) indicate that historical abundances were probably higher than at present.
3. Life History Features.
A. Breeding. Reproduction is aquatic.
i. Breeding migrations. Undocumented.
ii. Breeding habitat. Courtship has not been observed in the field, but it is likely that breeding occurs along the margins of low-order streams, springs, and seeps.
i. Egg deposition sites. Karraker (1999) reported an oviposition site beneath a mid-channel boulder in a first-order stream in Humboldt County, California. Large cobble was the primary substrate in the vicinity of the nest. Another clutch of eggs was found beneath a 42-cm diameter (longest dimension) boulder in a small, coastal stream in Humboldt County, California (G. Hodgson and L. Ollivier, unpublished data). Water temperature at the time of discovery was 10.4 ˚C, and gravel was the predominant substrate near the oviposition site.
ii. Clutch sizes. Clutch sizes for the California nest referred to above were 11 eggs (Karraker, 1999) and 8 eggs (G. Hodgson and L. Ollivier, unpublished data). Development of the eggs is slow, > 193–220 d (Karraker, 1999). Nussbaum (1969b) reported a hatch time of 210 d for eggs of Columbia torrent salamanders (R. kezeri) held at 8 ˚C in the laboratory.
i. Length of larval stage. Larval development takes 3.5 yr (Nussbaum and Tait, 1977).
ii. Larval requirements.
a. Food. Unknown, but probably similar to those of adults (refer to "Feeding Behavior" below).
b. Cover. The larvae of southern torrent salamanders are morphologically adapted to mountain brook microenvironments (Valentine and Dennis, 1964), which consist primarily of the shallow waters of springs, seeps, and headwater streams with cold (6.5–15 ˚C), low-velocity flows, over unsorted rock or rock rubble substrates, usually in mesic mature to old‑growth forests (Welsh and Lind, 1996, and citations therein).
iii. Larval polymorphisms. None reported.
iv. Features of metamorphosis. Smallest transformed individuals ranged from 30.2–38.6 mm SVL (Nussbaum and Tait, 1977). Good and Wake (1992) reported a similar range of 31.0–39.0 mm for museum specimens. The larval period is 3.0–3.5 yr (Nussbaum and Tait, 1977).
v. Post‑metamorphic migrations. Not known; at least some adults appear to remain in proximity to natal streams but also use adjacent riparian and moist upland habitats.
vi. Neoteny. Not reported.
D. Juvenile Habitat. Similar to larvae and adults (see "Larval requirements" above and "Adult Habitat" below).
E. Adult Habitat. Adults, while occasionally found in adjacent moist riparian vegetation, are usually found in contact with cold (6.5–15 ˚C) water in springs, seeps, and headwater streams with shallow, slow flows, over unsorted rock or rock rubble substrates, in mesic mature to old‑growth forests of the Pacific Northwest (Welsh and Lind, 1996, and citations therein; but see Diller and Wallace, 1996). Stebbins and Lowe (1951) generalized about the vegetation assemblage associated with streams that supported Rhyacotriton, noting that it typified riparian conditions that provide a cool, wet microenvironment. This requirement is probably related to the fact that species in the genus Rhyacotriton are the most desiccation intolerant salamanders known (Ray, 1958), a condition that may be linked to a high dependence on skin surfaces for oxygen uptake (average = 74%) as the lungs are highly reduced (Whitford and Hutchison, 1966b). Corn and Bury (1989a), Welsh and Lind (1996), and Welsh and Ollivier (1998) documented the importance of a lack of fine sediments (e.g., sand and fine gravel) which fill in the coarse substrate interstices of the streambed used for cover by both larval and adult salamanders. Diller and Wallace (1996), sampling within commercial timberlands in the coastal redwoods of California, purported to demonstrate a relationship between the presence of southern torrent salamanders and types of parent geology (harder substrate types were more likely to support salamanders) and stream gradient (steeper stream channels were more likely to support salamanders; see also Brode, 1995). Welsh et al. (2000) tested both of these hypotheses using data from across a larger portion of the range of southern torrent salamanders. They found no relationship with gradient or parent geology and concluded that Diller and Wallace’s (1996) outcome was the result of their sampling only on harvested commercial timberlands. This limited sampling regime resulted in Diller and Wallace (1996) detecting relationships that were artifacts of the long timber harvesting history in California’s coastal redwoods, which has had pronounced negative effects on the amounts and distributions of suitable stream environments for southern torrent salamanders (Welsh et al., 2000).
F. Home Range Size. Welsh and Lind (1992) marked a total of 188 individuals, recapturing 21% over 3 yr, and found little movement for both larvae and adults (2.2 m/yr and 1 m/yr, respectively). They found that 52%, 32%, and 16% of this movement was downstream, upstream, or lateral or no net movement, respectively. However, they cautioned that they had no way of determining distances moved by the large portion of animals that either dispersed out of their 12.6 m2 study area or possibly met other fates such as predation.
G. Territories. No studies have addressed whether or not they are defended.
H. Aestivation/Avoiding Dessication. Except at coastal sites, both larval and adult southern torrent salamanders appear to burrow deeper into streambed substrates in response to warmer water temperatures and lower stream flows associated with summer climate shifts. It is not known whether they are active in the hyporheic zone at interior sites during the summer, but Welsh and Lind (1992) reported a significantly greater weight gain over the winter compared with the summer for both larvae and adults, suggesting a period of inactivity during the hotter and drier summer season.
I. Seasonal Migration. No studies have addressed whether these salamanders migrate seasonally, but anecdotal evidence indicates that adults may move between headwater and adjacent upland habitats (personal observations).
J. Torpor (Hibernation). Southern torrent salamanders appear to retreat deeper into stream channel substrates during winter in response to high stream flows, but it is not known whether they remain active in these hyporheic zone refugia. Welsh and Lind (1992) reported over-winter weight gains for both larvae and adults, suggesting that southern torrent salamanders may be active throughout the winter.
K. Interspecific Associations/Exclusions. Pacific giant salamanders (Dicamptodon tenebrosus) are known to feed on southern torrent salamanders, and Stebbins (1953) and Nussbaum (1969b) speculated that the selection of shallow water microhabitats on the part of southern torrent salamanders was a response to this predation. Welsh (1993), in an analysis of Pacific giant salamander habitat associations, reported a weak negative association between these two species, giving credence to this exclusion hypothesis (Stebbins, 1953; Nussbaum, 1969b). A similar analysis of southern torrent salamander associations showed a weak but non-significant (p = 0.09) reciprocal relationship (Welsh and Lind, 1996).
L. Age/Size at Reproductive Maturity. Nussbaum and Tait (1977) reported that southern torrent salamanders take 4.5–5.0 yr to reach sexual maturity; 3.5 yr in the larval form and 1–1.5 yr after metamorphosis. Adults measured 35–52 mm SVL (n = 49; Welsh and Lind, 1992).
M. Longevity. No direct measurements are available, but the long maturation time suggests that this is a relatively long‑lived species.
N. Feeding Behavior. Adult southern torrent salamanders eat primarily aquatic and semi‑aquatic insects, a large portion of which are amphipods and Collembola; they feed mostly on the larval and nymph life stages (Bury and Martin, 1967).
O. Predators. Pacific giant salamanders (see "Interspecific Associations" above) and probably garter snakes (Thamnophis sp.) and salmonid fishes (Oncorhynchus sp.).
P. Anti‑Predator Mechanisms. Stebbins (1953) and Nussbaum (1969b) speculated that the confinement of this species to shallow water flowing through rock rubble may be a response to predation by larval and paedomorphic Pacific giant salamanders.
Q. Diseases. None described.
R. Parasites. Unknown. One species of monogenoidean fluke, previously unique to the genus Rhyacotriton, has also been described from Cascade frogs (R. cascadae) from southern Washington (Kritsky et al., 1993). Several digenean flukes have been collected from various species of Rhyacotriton (Senger and Macy, 1952; Anderson et al., 1966; Martin, 1966b), and the nematode Oxyuris dubia (Lehmann, 1956).
4. Conservation. Petitions to list southern torrent salamanders under both the Federal Endangered Species Act and that of the State of California, based on both loss of habitat and population declines due to forestry practices, were filed in 1994. Noting that the petition had merit, the California Department of Fish and Game determined the following objectives required addressing: (1) document existing localities; (2) determine populations and habitat status; (3) examine population trends; and (4) determine adequacy of current forest practice rules to protect the species and its habitat. However, following a status report (Brode, 1995) that lacked appropriate statistical analyses of available data, adequate scientific review, and the lack of clear and concise recommendations for modification of timber harvest rules to insure reversal of declines, California Department of Fish and Game Commission opted not to list the species, promising instead to address problems in its forest practices act that affected torrent salamanders (see Welsh et al., 2000). These problems remain unaddressed to date (Welsh, 2000). The U.S. Fish and Wildlife Service recently issued their "12-month finding" on the Federal petition (Federal Register, June 6, 2000) and also concluded that a listing was not warranted. In both the state and federal status reviews, each locality record was considered a population, so the number of extant populations used to make these findings was overestimated. The federal finding reported no results for objectives 2, 3, or 4. Consequently, this finding is based not only on an inflated estimate of population numbers, but also has no landscape-scale analysis of the species' metapopulation structure, no determination of population trends, and an incomplete analysis of the adequacy of the California Forest Practice Rules to protect southern torrent salamanders (Welsh et al., 2000). This finding does assert that incorrect classification of streams could result in the application of inadequate protection measures to streams potentially containing southern torrent salamanders. However, no assessment is made of the problem of stream misclassification or of the associated impacts to southern torrent salamanders. Because of inadequacies in these findings, and because headwater streams, seeps, and springs receive little protection under the California Forest Practice Rules (Welsh, 2000), it is likely that populations will continue to be extirpated due to timber harvesting and related land-management practices. Such extirpations will further fragment the already disparate metapopulation units of this species (Welsh and Lind, 1992), resulting in their increased isolation and decreased any potential for gene flow. This scenario will likely result in these subpopulations disappearing across the landscape, as already appears to be the case in Mendocino County (H.H.W. and colleagues, unpublished data) and the Mattole watershed of Humboldt County (Welsh et al., in preparation).
1Hartwell H. Welsh Jr.
2Nancy E. Karraker
Literature references for Amphibian Declines: The Conservation Status of United States Species, edited by Michael Lannoo, are here.
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Citation: AmphibiaWeb. 2019. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Jun 2019.
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