| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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Wild Lives Giant SalamandersSubmerged in a foot of oxygenated water with his head angled into the shadowy corner of its tank, floated one of the world's largest amphibians. Resembling a gill-less mud puppy on steroids, this two-and-a-half-foot- long, chocolate-brown beast looked like the reclusive star of some sci-fi film, ready to trample a metropolis. We had driven three hours from Seattle to the Vancouver Aquarium in British Columbia, Canada, to see this guy. And he was well worth the trip. Most of the roughly 320 different species of salamanders inhabit the temperate regions of the Northern Hemisphere and reach only four to six inches in length. They belong to the oldest order of existing terrestrial vertebrates, Caudata, which can be traced back more than 350 million years. Based on their bone structure and pattern of external fertilization, the giant salamanders or Cryptobranchidae are among the most primitive of all salamanders. Included in this relict group are the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (A. japonicus), and the hellbender (Cryptobranchus alleganiensis), native to North America. Besides having an ancient lineage, giant salamanders are the longest-lived amphibians; one captive Japanese specimen survived for 55 years. "North America boasts an assortment of big, bizarre salamanders that look more like bad dreams than live animals," wrote herpetologist Roger Conant. "Since all are aquatic and nocturnal, few persons other than fishermen ever meet them." One of the biggest is the two-foot-long hellbender found in streams and rivers of the Ozark and Allegheny mountains. Believing them to be poisonous, fishermen will often cut their lines and abandon their gear when they hook one. However, these harmless, but extremely slimy animals are easy to catch--if you can simultaneously grab their neck and immobilize their front legs. Despite such misguided fears, hellbenders are still relatively abundant. Both of the Asian species, however, are endangered and protected. In l725, when the first fossil salamander was discovered in Germany, it was mistakenly identified as human--thought to be a fossilized victim from Noah's flood. Subsequent research dated the specimen to the Miocene period l5 million years ago. The bones, it turns out, belonged not to a hominid, but to an extinct cryptobranchid named Andrias scheuchzeri. Since then, fossils of giant salamanders have been found in Europe, Asia, and North America--reflecting their widespread prehistoric distribution. Cryptobranchids have been described as squat, ungainly animals that never completely metamorphose. Typical of all larval salamanders, the adults lack eyelids and retain their larval teeth. The large head is extremely broad and flat. The limbs are short and stocky and the tail is laterally compressed. A distinctive wrinkled ridge of skin runs along the sides of the head and body. Loaded with blood vessels to draw oxygen from the water, the wrinkled skin increases surface area for oxygen absorbtion. "Well aerated water is important in maintaining captive animals," says herpetologist Ed Maruska, director of the Cincinnati Zoo--home to the largest collection of cryptobranchids in the United States. "You can tell when the salamanders are oxygen depleted by their behavior. They will rock back and forth to create their own aerating current." The Chinese giant salamander is the most widely distributed of the three species. It dwells in fast mountain streams at 200 to l,000 meters above sea level in the tributaries of the Yangzi, Yellow, and Pearl rivers across 17 provinces and regions of China. The five-foot-long salamanders inhabit the dark, muddy rock crevices along the riverbanks, facing outward to feed and for self-defense. These nocturnal carnivores gulp frogs, crabs, fish, shrimp, snakes, aquatic insects, water rats, and turtles. In turn, the 60-pound amphibians often end up under the knife at local Chinese fish markets--their flesh considered a delicacy and their body parts used in traditional medicines. Designated a Special Natural Monument, the Japanese giant salamanders have been given full legal protection. They inhabit the cold, fast-flowing mountain streams and rivers of northern Kyushu Island and western Honshu. By day the mucus-covered salamanders rest in caves in the river bank, or under large rocks. At night they emerge from their dens to gulp bottom-dwelling loach and other fare. Cryptobranchids have dramatic feeding behavior. According to Maruska, the water literally explodes when a salamander suddenly opens its mouth to gulp prey. Scientists studying them have discovered unique and spectacular asymmetries in the salamander's jaw and the hyoid movements made during this rapid suction feeding. Depending on the position of the prey, the animal can rapidly and forcefully open and close one side of its mouth independently and bend its mandible forward by as much as 40 degrees. This action generates the necessary force to capture prey, and Maruska has seen an unwary keeper's finger badly mangled by a giant salamander. Giant salamanders are unusual for amphibians in that they lay their eggs in early autumn. A small breeding migration of Japanese giant salamanders begins in late August when "herds" congregate at nest sites. A dominant owner male prepares and occupies each spawning pit, a submerged, sandy depression at the end of three-foot-long horizontal tunnel in the mud. As a result, fights often occur between males over access to this scarce resource. Males lose toes and limbs in the battles and some die from bites to their heads and necks. According to Kazushi Kuwabara, past director of the Asa Zoo in Hiroshima, Japan, an elaborate mating ritual takes place when a gravid female visits a nest to lay her eggs. Shortly before she produces her bead-like string of light yellow eggs in transparent jelly, the female starts to turn and spin with the resident male. Other males are allowed into the nest to join the spinning pair as the female arches her back and starts releasing eggs for the males to fertilize. The spinning amphibian mass accelerates until the eggs are spawned and slows as the males cover the eggs with milt. This process repeats until the female has deposited all of her 400 to 500 eggs, then departs. The eggs of several females may be deposited in the same nest, which the resident male aggressively guards until they hatch and larvae leave the nest the following February. Biologists from the Asa Zoo have studied Japanese giant salamanders in the wild and have successfully bred them since 1979 in tanks that allow both sexes to move and mingle. The Cincinnati Zoo received a handful of larval Japanese giant salamanders from the Asa Zoo in the l980s. Cincinnati plans to try naturally breeding the now sexually mature salamanders this year. If this fails, they hope to establish artificial spawning techniques on the more abundant hellbenders, and then apply the technology to the endangered Asian species. Andrew Short, an animal care specialist at the Vancouver Aqaurium, has taken care of the facility's one Japanese specimen for the past five years. Short had waited a few hours to feed their lone giant, in hopes that I might see some interesting behavior. I doubt the animal suffered. Because the reptile's metabolism is so slow, it is usually fed just once a week. Short lowered a piece of herring into the tank, but on this occasion the only clue that the salamander had eaten was the sideways wagging of its tail. The Vancouver salamander slowly backed out of the corner and approached the front of the tank. Covered with tubercles, its huge, flattened head looked like a coral reef, its tiny, bead-sized white eyes lost in the texture. The brown wrinkled giant lingered at the glass, a more alien-looking creature hard to imagine. Seattle-based Barbara Sleeper is a natural sciences writer specializing in animal behavior and wildlife conservation. |
Winter 1997
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