Frogs v. trout

Natural History, Oct, 2004 by Chris Sherman, James P. Collins

In his story "Where Have All the Frogs Gone?" (6/04), James P. Collins neglected to mention another possible answer to his question, namely, the losses attributable to predation by the nonnative species of fish intentionally introduced for sport fishing into many lakes. Many western U.S. lakes, for instance, have been stocked with rainbow trout. It is becoming increasingly well documented that such fish prey on the native frogs. The fish thrive, to the delight of the fishermen, but the frogs dwindle, perplexing biologists who are looking for more complicated explanations.

Chris Sherman

St. Louis, Missouri

JAMES P. COLLINS REPLIES: It is the rare situation in which only one factor is responsible for amphibian declines. In most cases, two or more out of six factors are involved. The California red-legged frog illustrates how three causes--commercial exploitation, exotic species, and land-use change--interacted to the detriment of the frogs.

Introducing trout in many western U.S. lakes is a particularly clear example of how exotic species can adversely affect native frogs through predation. But it is worth remembering that even in this seemingly straightforward, single-factor case, the reasons for introducing the fish are, in part, commercial ones (recreation brings tourism), and there is some evidence supporting the concern that introduced trout carry pathogens lethal to amphibians.