Global Decline

Last Review/Updated: May 30, 2002

Around the world, there has been concern about declines in the abundance of various species of amphibians. Because so little is known about the health and stability of most populations of amphibians there is little known about how widespread a global decline in amphibians really is. However, it appears that species are declining in not only developed areas, where amphibians must compete with human activity, but also in pristine areas, where the water should be unpolluted. This raises the possibility of one or more world-wide phenomena striking wetlands around the globe.

Amphibians have a complicated life history, developing from completely aquatic creatures to mainly terrestrial ones, and they have permeable skin. Because of this, they act as the proverbial canary in a coal mine, indicating the relative health of their environments. A number of different causes for a global decline in amphibians have been suggested:

  • Acid Rain. Acidic precipitation can also fall as snow. When it melts in the spring, it can send a pulse of highly acidic water into breeding ponds possibly damaging amphibian eggs.
  • Airborne Pesticides. As merely one example, the pesticide DDT has been found in many areas far from where it was ever sprayed. Even though banned in North America it is still used in many countries.
  • Ultraviolet Light. The reduction of the ozone layer in the atmosphere leads to increased ultraviolet light reaching the Earth's surface. In humans this can lead to increases in the occurrence of cataracts and skin cancer. In amphibians it may cause damage to eggs floating in ponds.
Whether there is one single cause, or more likely, a number of different regional causes, it is vital to understand whether this is a signal of greater global change. To that end the Declining Amphibian Populations Task Force (DAPTF) was established by the Species Survival Commission of the International Union for the Conservation of Nature (IUCN). Its mandate is to organize a world-wide monitoring program for amphibians to determine four things:
  1. the status of amphibian populations;
  2. the implications of any declines;
  3. the potential causes of these declines; and
  4. policy recommendations based on these findings.
To date there are national working groups in a variety of countries, including Australia, the Netherlands, South Africa, the United Kingdom, and the USA. In Canada a national working-group has also been formed and there are now coordinators for every province and territory.

In Alberta, even the historical distribution for some species is somewhat vague, especially for northern parts of the province. Declines in some species have already been documented, most notably for the northern leopard frog, which vanished from many sites around the province in the late 1970s, and the Canadian toad, which has declined in the parkland regions.

In order to determine the relative stability of provincial amphibian populations, long-term monitoring of various sites is required. Single estimates of amphibian populations are often misleading because the number of amphibians can fluctuate dramatically from year-to-year, generally in response to the weather. Dry years will tend to reduce population size and wet years may result in large increases in population. Because of this, establishing a long-term monitoring program for a variety of species is important to determine the trend as opposed to just the annual variations.

If you are interested in helping monitor amphibian populations in Alberta, see Amphibian Monitoring Project.

Introduction | Identifying Amphibians | Biology of Amphibians | Global Decline
Amphibian Monitoring Project | RANA Project