Dicamptodon tenebrosus
Coastal Giant Salamander
(Also: Pacific Giant Salamander)

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. (Bishop, 1947; Carl, 1959)

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. (Corkran and Thoms, 2006)

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. (Green and Campbell, 1984; Petranka, 1998; Wood, 1972)

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. ("Wildlife at risk in British Colombia: Pacific giant salamander", 1993; Lannoo, 2005; Sagar, et al., 2007)

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. (Petranka, 1998)

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. ("Wildlife at risk in British Colombia: Pacific giant salamander", 1993; Blood, et al., 1993; Lannoo, 2005; Petranka, 1998)

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. (Nussbaum, 1969; Nussbaum, 1969)

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. (Lannoo, 2005)

The newly metamorphosed and sometimes paedomorphic individuals move out of streams during rainy, wet periods. Some will remain in the vicinity of the streams while others go to higher ground. Both the larvae and adults seek refuge from temperature extremes such as in winter during freezing temperatures.

Pacific giant salamanders are mostly nocturnal, though may be active during the early morning hours as well. Female salamanders will perform migrations to suitable streams for oviposition, but currently this seems to be the only migrational behavior for this species. As most salamanders live within 50 m of a stream, these migrations are not significant and the species is considered sedentary.

From what is known of these salamanders, they lead largely solitary lives but individuals will come together to breed. They exhibit very territorial behaviors and will forcefully guard burrows from intruders. (Lannoo, 2005)

It has been documented that the home range size of this species is between 3,047 and 5,196 metres squared. ("Wildlife at risk in British Colombia: Pacific giant salamander", 1993; Lannoo, 2005)

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. (Lannoo, 2005; Petranka, 1998)

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. (Lannoo, 2005; Parker, 1994; Petranka, 1998)

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. (Lannoo, 2005)

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. (Lannoo, 2005; Petranka, 1998)

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. (Petranka, 1998; Pimentel, et al., 2005)

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

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. ("Recovery strategy for the Pacific Giant Salamander (Dicamptodon tenebrosus) in British Columbia", 2010; Petranka, 1998)

Pacific giant salamanders are known to hybridize with Californian giant salamanders in a few of the streams of southern Medocrine County in California. They are known to be sympatric with Cope giant salamanders across the range of Cope giant salamanders. (Lannoo, 2005)