Dicamptodon tenebrosus

This salamander is the largest terrestrial salamander in the Pacific Northwest and one of the largest terrestrial salamanders in the world (Petranka 1998). Body stout and powerful. Smooth skin. Dorsal ground color is dark brown or gray to black with well defined irregular marbling of purple to reddish brown. Degree of marbling varies among individuals and among populations. Underside is usually light colored: lightish brown to off-white. The posterior half of the tail is laterally compressed, and the head is depressed in front of the eyes.

Larvae generally measure from 33 mm TL up to 30 cm which is the size of some untransformed adults (Petranka 1998). They have tail fins that extend forward to the insertion of the hindlimb. The gills are bushy and purplish to red. Ground color of larvae is light to dark brown. The larvae frequently have a yellow stripe behind the eye, and the toe tips are covered with dark, cornified skin (Nussbaum 1976) . Some older larvae are mottled.

Dicamptodon tenebrosus has until recently been included in D. ensatus, but recent genetic research has shown that the coastal Giant Salamander consists of two distinct species, D. tenebrosus to the north and D. ensatus to the south (Good 1989). These two species interbreed over a 4.7 km contact zone near Anchor Bay in Mendocino Co., CA, but there is very little gene flow (Good 1989). There is a hybrid deficiency and there is little evidence of introgression outside the narrow hybrid zone (Petranka 1998).

This species is remarkable in their gregariousness, their formidable bite, their production of a "bark" (Stebbins 1951 1985), their large size, and their consumption of mammals and other amphibians.

More work is necessary to determine the impacts that logging has had and the impacts that future logging could have on the abundance of this species.

See another account at californiaherps.com.

Near sea level to ca. 7000 ft. (2160 m). From extreme sw British Columbia to northern Sonoma County in California (Good 1989).

Adults inhabit damp, dense forests (esp. Coastal Redwood and Douglas Fir), usually in the vicinity of streams or seepages. Found under logs, rocks, bark, or other objects or sometimes crawling in the open. Occasionally climbs and has been recorded to a height of 8 ft. (Stebbins 1951). Larvae are found in small to medium sized creeks and streams in habitat similar to that in which adults are found.

This species occurs from Western North America from southern British Columbia (Chilliwack River drainage) south through western Washington and western Oregon to northwestern California (Good 1989; Farr, 1989 COSEWIC report; Petranka 1998).

Pacific giant salamanders occupy the coastal areas of British Colombia, Oregon, Washington, and northern California. In British Colombia, these salamanders are only found in the extreme southwest region, south of the Fraser valley and in the Chilliwack district.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000-2,500,000 square km (about 80,000-1,000,000 square miles)) Southern British Columbia (Chilliwack River drainage) south through western Washington and western Oregon to northwestern California (Good 1989; Farr, 1989 COSEWIC report; Petranka 1998).

Pacific giant salamanders are the largest terrestrial salamander in the Pacific Northwest and are one of the largest terrestrial salamanders in the world. Adults of this species may exhibit neoteny and retain gills to live a more aquatic lifestyle, or may metamorphose completely and live terrestrially. Gilled, aquatic adults are common in more coastal populations and in those of British Columbia.

The dorsal surface of most adults is dark brown to nearly black and is covered with light brown spotting or marbling, though coloration varies between individuals and populations. The ventral side is unmarked and white or pale in color. Young salamanders have bright golden marbling that becomes more diffuse and more conspicuous with age. The pattern may fade in very old adults but they usually retain some spotting on the head. Larval salamanders metamorphosize when they reach 92 to 166 mm in length.

Pacific giant salamanders have moderately broad heads, short blunt snouts, and medium sized eyes with brass-freckled irises. There is a guar fold; but there are no parotoid glands present in this species of salamander. They have large strong legs with no webbing or tubercles on the soles of their feet. They have 12 rather indistinct costal grooves on each side of the body. The tail makes up two fifths of the body length. The tail is stout and laterally compressed, and males of the species have slightly longer tails than the females. Adults measure 6.25 to 17 cm snout-vent length (SVL) and may reach 34 cm in total length. Adult mass ranges from 22 to 114 g.

In addition, Pacific giant salamanders have a basal metabolic rate of 31.2 +or- 4.3 at a temperature of 15 degrees Celsius. The value for basal metabolic rate is temperature dependent.

Range mass: 22 to 114 g.

Range length: 34 (high) cm.

Range basal metabolic rate: 20.7 to 63.3 cm^3 oxygen/hour.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous

Sexual Dimorphism: male larger

Length: 30 cm

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

Pacific giant salamanders live in small to midsized streams. They also occupy moist, riverside forests. The type of stream bed they prefer is composed of large gravel to small boulders having some large logs in them with very little silt on the bottom of the stream. During rainy periods this species may also be found under forest litter such as leaves and small branches. This species can be found at elevations from sea level to 1830 m.

Range elevation: sea level to 1830 m.

Habitat Regions: temperate ; terrestrial ; freshwater

Terrestrial Biomes: forest

Aquatic Biomes: rivers and streams

Other Habitat Features: riparian

Comments: Larvae and paedomorphic adults usually inhabit clear, cool or cold, well-oxygenated streams and often take cover under stones (Parker 1991); aquatic stages also occur in some mountain lakes and ponds. Larvae may occupy wet sub-benthic habitat (interstitial spaces among substrate particles) of intermittent streams when water is not flowing on the surface (Feral et al. 2005). Metamorphosed adults are found in humid forests under rocks and logs, etc., near mountain streams or rocky shores of mountain lakes (Stebbins 1985).

Eggs are attached to logs or rocks in creeks (Nussbaum and Clothier 1973, Jones et al. 1990).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Migrates between aquatic breeding and terrestrial nonbreeding habitats.

The larvae of the species will consume a variety of invertebrate prey in a wide range of sizes. They will consume insect larvae and adults, amphipods, ostracods, termatoes, mollusks, and crayfish. Larger larvae will prey on some salmonids, sculpins, and salamanders. Adult diets are dominated numerically by aquatic organisms but they consume a higher volume of terrestrial prey. Terrestrial adults emerge from logs and other surface cover on rainy nights and forage the forest floor. Individuals of this species may forage one and a half to two meters above the ground on tree trunks. Large terrestrial members of the species can handle eating small mammals such as mice and shrews or even snakes. Pacific giant salamanders are sit and wait predators who quickly lunge short distances in order to obtain prey.

Animal Foods: mammals; amphibians; reptiles; fish; eggs; insects; other marine invertebrates

Primary Diet: carnivore (Eats terrestrial vertebrates)

Comments: Larvae feed on a wide variety of aquatic invertebrates as well as terrestrial invertebrates that fall into the water (Parker 1994) and some small vertebrates (e.g., fishes, tadpoles, other larval salamanders). Adults eat terrestrial invertebrates, also small snakes, shrews, mice, and salamanders, etc.

Pacific giant salamanders likely impact prey populations of aquatic and terrestrial vertebrates, as well as aquatic invertebrates. High frequency of small mammals in the diet of large, terrestrial adults suggests that these salamanders may play a role in structuring the shrew and mice communities. Parasitic helminths have been found in this species.

Commensal/Parasitic Species:

• Helminths

Natural predators of Pacific giant salamanders are weasels, river otters, water shrews, garter snakes (Thamnophis genus), salmonids and conspecifics. When approached by predators salamanders employ a variety of anti-predator adaptations. These include tail lashing, biting, arching of the back, and skin secretions. They are also known to emit a warning bark. Their black and brown marbled coloration is cryptic in their terrestrial and aquatic habitats.

Known Predators:

• Weasels
• Garter snakes (Thamnophis genus)
• Salmonids
• Pacific giant salamanders (dicamptodon tenebrosus)
• Water shrews
• River otters

Anti-predator Adaptations: cryptic

10,000 - 1,000,000 individuals

Comments: Total adult population size is unknown but likely exceeds 10,000. Larvae are often abundant and are far more common than the adults.

When disturbed by predators Pacific giant salamanders will emit a "bark". When approached by a predator, individuals strongly arch their bodies and may thrash their tails to threaten the predator. They can also secrete a noxious substance from their tails to ward off predators. The adults of this species will also head butt and bite viciously. They often produce a rattling or growling sound while snapping their jaws and lashing their tail. Little information exists about the communication between members of this species.

Communication Channels: visual ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

Comments: In northern California, larvae were active on the streambed surface at night, inactive and under cover during daylight (Parker 1994).

Little is actually known about the development of Pacific giant salamanders. It is known that environmental conditions (such as the cold temperature of preferred streams) affect the growth and survival of the larvae. After they are laid, the eggs may take up to 7 months to hatch. Larvae are 3 cm long upon hatching and feature large yolk sacs that will sustain them for 2 to 4 months. At this point, the young are about 40 cm in length, and can begin to hunt their own prey. Metamorphosis begins 18 to 24 months after hatching, when the young are 92 to 166 mm in length.

Pacific giant salamanders exhibit slow growth rates and do not reach sexual maturity until 5 or 6 years of age. Adults of this species may be terrestrial or aquatic; the aquatic being neotenes which retain many larval characteristics like external gills. Neoteny seems to be more prevalent in certain, more coastal populations, specifically, British Colombia salamanders are nearly all neotenes.

Development - Life Cycle: neotenic/paedomorphic; metamorphosis

Nothing is yet known about the lifespan of Pacific giant salamanders however, other species of aquatic salamander are known to be long-lived. Given that the young take 5 to 6 years to reach reproductive maturity, they are likely a long-lived species as well.

Very little information is available about the mating system for Pacific giant salamanders. Courtship occurs from spring to fall, and reproductively mature, terrestrial females will migrate to streams to oviposit. Field observations have suggested that the courtship ritual occurs terrestrially in crevices under rocks and logs, however, the courtship behavior has not been directly observed.

When it is time for the females to ovipost they migrate from upland habitats to streams. It is unknown if these salamanders breed yearly as the females have a significant parental investment of guarding her eggs for up to 7 months. Most females appear to oviposit during early to mid May then they guard their eggs until hatching. The few nests that have been discovered have been in subterranean habitats in running water. These salamanders have one of the longest incubation periods of all salamanders. Hatchlings appear in December and January about 6 to 7 months after oviposition. It takes 5 to 6 years for Pacific giant salamanders to reach sexual maturity.

Breeding interval: The breeding interval for Pacific giant salamanders is unknown.

Breeding season: Pacific giant salamanders breed from spring through fall, with high altitude populations breeding later.

Range number of offspring: 83 to 146.

Range time to hatching: 6 to 7 months.

Range age at sexual or reproductive maturity (female): 5 to 6 years.

Range age at sexual or reproductive maturity (male): 5 to 6 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous

After mating terrestrially, female Pacific giant salamanders will migrate to fast-flowing streams to lay their eggs. The females will guard the aquatic clutches until the young hatch after 6 or 7 months. Cannibalism is well documented among the males of the species, which may explain why the female is in attendance.

Parental Investment: female parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

Breeds in both spring and fall. Lays clutch of 100-200 eggs in spring. Female attends eggs until hatching. At an elevation of 275 m in Oregon, a clutch with limb-bud-stage embryos was found in mid-July; hatching occurred by mid-September (Jones et al. 1990). Larvae metamorphose usually in 18-24 months, but sometimes they become sexually mature in the larval stage (Nussbaum et al. 1983, Stebbins 1985).

Year Assessed

Assessor/s

Reviewer/s

Justification

In the United states, Pacific giant salamanders are considered of "least concern" to the IUCN Red List and are not protected federally or by CITES. Populations are currently stable but have become fragmented as a result of forestry in their habitats. However, several studies have indicated that populations of Pacific giant salamanders decline after the logging of old growth forests. Both terrestrial and aquatic populations are affected by logging as their habitats suffer from decreased canopy cover which likely alters temperature, moisture, and degree of siltation. Studies have shown that this species is far more abundant in un-silted streams compared to heavily silted streams.

In British Colombia however, Pacific giant salamanders are considered nationally imperiled and are included in the Canada Species at Risk Act. They are considered important in conserving the biological diversity of native ecosystems in the region. To address these concerns, the British Colombia Ministry of Environment created a management strategy in April 2010 to ensure a self-sustaining population in southwest British Colombia.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N2 - Imperiled

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Common in many areas and still well distributed throughout the historical range from southwestern British Columbia to northwestern California.

Intrinsic Vulnerability: Moderately vulnerable

Environmental Specificity: Narrow. Specialist or community with key requirements common.

Adults are remarkable for salamanders in their voracious feeding habits. Small rodents such as shrews and mice are regular prey, as are other amphibians, insects, snails, and slugs (Leonard et al. 1993; Petranka 1998). Diller (1907) observed an eight inch Dicamptodon with a two foot garter snake in its jaws, held by its head and neck. It is more likely, however, that the salamander was defending itself rather than feeding on the snake, as garter snakes are common predators of Dicamptodon. See references in Petranka (1998).

Adults are very good diggers and likely burrow at the base of a spring upon arrival of the autumn rains. Indeed, adults have been found under ground at a depth of 20 ft. (Dethlefson 1948). Nests of 83 and 146 eggs, attended by females, have been found in rocky areas nears streams and seeps. One nest was under rocks 3 feet from the surface. Egg deposition is in the spring (early May) and hatching may occur up to 9 months later (Nussbaum 1969).

Adults are very powerful and can inflict a painful bite when handled. They are also known to emit an audible growl or bark when threatened (Stebbins 1951 1985). Adults are relatively rare and are a good find even in prime habitat, especially considering the abundance of the larvae in streams of the Pacific Northwest. Larvae are mainly found in small to medium sized mountain streams (Nussbaum and Clothier 1973) and are most common in areas where stones and cobbles cover the stream bottom with little silt (Murphy and Hall 1981). Censuses by Murphy et. al. (1981) showed that D. tenebrosus larvae are the dominant vertebrate fauna in terms of biomass in the Cascade Mountain Streams that were sampled.

Predators include fish, common garter snakes (Thamnophis sirtalis), northern water shrews (Sorex palustris), river otters (Lutra canadensis), weasels (Mustela) and other Dicamptodon (Nussbaum et al. 1983).

Population

Population Trend

Degree of Threat: Medium

Comments: Logging and road construction may result in unfavorable increases in water temperature and siltation (Welsh and Ollivier 1998). Abundance is much greater in old growth and mature forests than in young forests (see Petranka 1998).

The primary threat to Dicamptodon is logging. Larvae are approximately four times more abundant in streams passing through unlogged versus logged stands (Corn and Bury 1989). In addition, larvae were present in all the unlogged streams, but were absent from 30% of logged streams. The species is far more abundant in unsilted versus heavily silted streams (Hawkins et al 1983). In high gradient streams populations may increase for the first five to seventeen years after logging due to increase in primary productivity (Murphy et al 1981). After canopy closure populations decline below numbers typical of old growth forests, due to increased siltation (Corn and Bury 1989). It may be difficult for adults to persist even in relatively good forest habitat if nearby logging ruins streams for the larvae. There has been a decline of D. tenebrosus populations in British Columbia due to habitat destruction by logging (Orchard 1992). Indeed this species is considered an endangered species in Canada (Munro 1993).

Major Threats

Conservation Actions

There are no known adverse effects of dicamptodon tenebrosus on humans.

Pacific giant salamanders are predators of small mammals including mice, which may be of economic benefit to humans, as mice have become a prevalent pest for farms, industries and homes.

There is evidence that indicates that logging and other human disturbance is harmful to Dicamptodon, especially since the larvae depend on streams that are likely to be adversely affected by logging. It is rare to find adults in disturbed habitat, such as in clearings or on roads.