PACIFIC GIANT SALAMANDERS: Dicamptodontidae

PHYSICAL CHARACTERISTICS

Pacific giant salamanders are large, strong salamanders that live as larvae for several years. Larvae (LAR-vee) are animals in an early stage that change body form in a process called metamorphosis (MEH-tuh-MORE-feh-sis) before becoming adults. After metamorphosis Pacific giant salamanders live on land. These salamanders are 7 to 14 inches (17 to 35 centimeters) long. There are only four species: the Idaho giant salamander, Cope's giant salamander, the California giant salamander, and the coastal giant salamander.

Pacific giant salamanders have a large head, a stout body, well-developed eyes, and large, thick legs. They have strong jaws and many small but well developed teeth. The tail is short for a salamander tail—about an inch (2.5 centimeters) shorter than the length of the head plus the body. The tail is flat from side to side and has a ridge along the top and the bottom. Adult Pacific giant salamanders are dark brown and often have blotches of different shades of gray. The belly is light brown or yellowish white.

The larvae of Pacific giant salamanders are somewhat flat from back to belly and are dark in color. The short, strong tail is flat from side to side and has a small fin. Larvae that live in small, rapidly flowing streams have short, bushy red gills, but those that live in lakes and large streams have large, filmy gills. Gills are organs for obtaining oxygen from water.

GEOGRAPHIC RANGE

Pacific giant salamanders live in the Pacific Northwest of North America from north of San Francisco, California, to the northern end of the Olympic Peninsula in Washington and from the southern Cascade Mountains of Oregon in the United States into the coastal mountains of southwestern British Columbia, but not on Vancouver and the neighboring islands, in Canada. Idaho giant salamanders are geographically separated from the other species and live in the mountains of northern Idaho and northwestern Montana, west of the Continental Divide in the United States.

HABITAT

Pacific giant salamanders live in wooded areas that have clear streams for larvae. Most of these salamanders live in coniferous woodlands, or those covered with trees that bear their seeds inside cones. These salamanders do especially well in areas with Douglas firs and redwoods. Adult Pacific giant salamanders live under rocks or logs. The larvae usually live in small, trout-free streams, but larger larvae may live in rivers and small lakes.

DIET

The larvae of Pacific giant salamanders eat the larvae of any bottom-dwelling insects they find, but they also eat other stream-dwelling animals. Because they grow to a large size, the salamander larvae feed on larger prey as well, including small fish and the larvae of mole salamanders. Small adult Pacific giant salamanders eat land-dwelling invertebrates (in-VER-teh-brehts), or animals without backbones, which they catch with their long, fast tongue. As they grow larger, Pacific giant salamanders prey on vertebrates, or animals with backbones, such as slender salamanders, lizards, shrews, mice, and even snakes, which they seize with their strong jaws. Pacific giant salamanders travel to find food and can climb as high as 6.6 feet (2 meters) on tree trunks.

SILTATION

Siltation (sihl-TAY-shun) is what happens when soil is washed from land and builds up in streams and rivers. The buildup is called silt and looks and feels like sandy dirt. Siltation happens when river or stream banks do not have enough plant life on them to keep the soil in place, as when all the nearby trees are cut down, grazing livestock eat all the grass away, or when the soil is not healthy because of poor farming practices or drought.

BEHAVIOR AND REPRODUCTION

Adult Pacific giant salamanders are active at night, but sometimes they are found walking by day in dark, moist forests. Large Pacific giant salamanders can be aggressive, head butting and tail-lashing one another and inflicting severe bites to defend themselves from predators. Adult Pacific giant salamanders bark sharply, but scientists do not know why they make this sound.

Scientists are not sure how Pacific giant salamanders mate. They do know that the males place sacs of sperm on land and that fertilization (FUR-teh-lih-ZAY-shun), the joining of egg and sperm to start development, takes place inside the female's body. The females lay eggs one at a time in groups of eighty or more under large rocks and logs. The fertilized (FUR-teh-lyzed) eggs develop slowly, and hatching does not occur for many weeks. Newly hatched larvae probably do not feed for several weeks. Metamorphosis takes at least two years and sometimes as long as four years. Some Pacific giant salamanders do not go through metamorphosis; they keep the body forms they have as larvae. However, their reproductive organs mature, and they can breed.

PACIFIC GIANT SALAMANDERS AND PEOPLE

Pacific giant salamanders are rarely seen by humans, but the rare encounters are remarkable because the animals are impressively large and do not try to escape unless someone pokes them or tries to pick them up. Sometimes people find adult Pacific giant salamanders on the floors of dense coniferous forests during light rains. At other times the larvae are caught on hook and line by people who are fishing.

CONSERVATION STATUS

The World Conservation Union (IUCN) lists one species of Pacific giant salamanders as Low Risk/Near Threatened, or at risk of becoming threatened with extinction in the future. These salamanders depend on forests and clear, unpolluted streams. This habitat is being harmed by excessive logging, road building and other construction, and the spreading of cities. Salamanders are most abundant in old-growth forests, but they survive after logging as long as the streams remain relatively free of silt.

COASTAL GIANT SALAMANDER (Dicamptodon tenebrosus): SPECIES ACCOUNT

Physical characteristics: Adult coastal giant salamanders may be the largest land-dwelling salamanders. The head plus body length is more than 7.5 inches (19 centimeters), and the total length is at least 13 inches (34 centimeters). The largest coastal giant salamanders on record were larvae found in large rivers. These larvae were about 8 inches (20 centimeters) in head plus body length and nearly 14 inches (35 centimeters) in overall length. The color of coastal giant salamanders varies. The background color of larvae usually is dark brown to black. As metamorphosis approaches, a silvery or dull golden color appears over the dark base and produces a marbling effect of light on dark. The marbling varies from fine to coarse. In some cases the marbling is so coarse that the underlying color cannot be seen.

Geographic range: Coastal giant salamanders live in an area that extends from southwestern British Columbia, Canada, southward west of the crest of the Cascade Mountains to northern California, United States. Some of these salamanders live in isolated areas in north central Oregon, east of the Cascade crest.

Habitat: Coastal giant salamanders live in and near clear, cold, rocky streams.

Diet: Coastal giant salamanders mainly eat frogs and small mammals, but they also eat worms, insects, and spiders.

Behavior and reproduction: Adult coastal giant salamanders are active at night and are secretive, but they sometimes are seen walking through leaves on rainy days in densely forested regions. When approached, these salamanders bark. They are one of the few salamanders that make a sound. Coastal giant salamanders also can be found on rainy nights as they try to cross roads in areas near breeding sites.

Scientists know little about the breeding habits of coastal giant salamanders. Eggs are fertilized inside the female's body, so scientists believe males make a sperm sac that the females pick up. Females lay large numbers of large eggs under large rocks that are at least partially underwater in streams. The eggs take several months to hatch, and scientists believe the females guard their nests while the eggs are developing. After hatching, metamorphosis takes about two years. Some coastal giant salamanders do not go through metamorphosis, but even though they look like larvae, they can reproduce.

Coastal giant salamanders and people: Coastal giant salamanders are rarely found and are little known to people.

Conservation status: Coastal giant salamanders are not considered threatened or endangered. The greatest risk to these salamanders is destruction of forests and the buildup of silt in streams. ∎

FOR MORE INFORMATION

Books:

Bernhard, Emery. Salamanders. New York: Holiday House, 1995.

Duellman, William E., and Linda Trueb. Biology of Amphibians. Baltimore: Johns Hopkins University Press, 1994.

Gunzi, Christiane. Amphibians and Reptiles of North America. San Diego, CA: Thunder Bay, 1995.

Lawlor, Elizabeth P. Discover Nature in Water and Wetlands. Mechanicsburg, PA: Stackpole, 2000.

Llamas Ruiz, Andres. Reptiles and Amphibians: Birth and Growth. New York: Sterling, 1996.

Petranka, J. W. Salamanders of the United States and Canada. Washington, DC: Smithsonian Institution Press, 1998.

Web sites:

"Coastal (Pacific) Giant Salamander, Dicamptodon tenebrosus." Northern Prairie Wildlife Research Center.http://www.npwrc.usgs.gov/narcam/idguide/diteneb.htm (accessed on April 21, 2005).

"Dicamptodon (Strauch, 1870) Giant Salamanders." Livingunderworld.org.http://www.livingunderworld.org/caudata/database/dicamptodontidae/dicamptodon (accessed on April 21, 2005).

Guillermo, G.L. "Pacific Giant Salamander." Colegio Franklin Delano Roosevelt, American School of Lima. http://www.amersol.edu.pe/ms/7th/7block/jungle_research/new_cards/11c/report11c_G.html (accessed on April 21, 2005).