Fisheries biologists often stock fish in lakes and ponds where they find no fish. Our biologists were looking at Alpine lakes in the west that had disappearing amphibian popualtions. One researcher came across two guys who were state fisheries biologists. They use tadpoles as an indication that it needs fish. Agricultural chemicals, including pestitides, herbicides and fertilizers.
Fertilizers kill amphibians when they run off a field and into a pond.
Nutient levels build, blue-green algae blooms and amphibians die from lack of oxygen. Again, we have places where all these factors have played, but there are others where we haven't identified any cause. It is outrageously complex, and we don't have numbers to talk about populations. We do know things are collapsing in the West. This is one reason for the national monitoring program which Droege chaperones over the Internet.