Other Factors That May Be Harming Amphibians

Many studies indicate that amphibian declines are most prevalent in high-altitude areas, a finding that points to increases in ultraviolet radiation from the sun as a possible cause of some amphibian deaths and malformations. This intense form of light energy, which can cause genetic changes and other physical damage, is strongest at high altitudes, where there is less atmosphere to filter damaging solar rays. Ultraviolet radiation may have grown stronger in these areas since the 1970's due to the thinning of the ozone layer, a protective blanket of oxygen molecules that absorbs ultraviolet rays. Scientists believe that the ozone layer has been eroded by certain reactive chemicals--principally chloro-fluorocarbons--that have drifted into the upper atmosphere.

In December 1997, Oregon State University researchers reported that ultraviolet radiation was killing embryos (an early developmental stage) of the long-toed salamander in lakes of the Cascade Mountains. The scientists said that more than 90 percent of the embryos they studied that had been exposed to direct sunlight died before hatching or hatched with deformities. In contrast, almost all of the embryos that the researchers had shielded from sunlight with ultraviolet filters developed normally.

One last factor that should not be overlooked is the collection of amphibians--mostly frogs--for biological-supply companies and the food industry. The biological-supply trade provides dissection specimens for school classrooms. Such collecting is not well regulated and has reduced the number of frogs in many areas. Hunting frogs for their legs, a gourmet delicacy, has also depleted frog populations.

The various factors affecting amphibians do not occur in isolation. Scientists believe that several negative influences probably work in combination to push an amphibian population into decline. For example, pesticides and ultraviolet radiation could weaken amphibian immune systems, making them more vulnerable to bacterial infections and parasitic diseases.