Effects of rainbow trout (Oncorhynchus mykiss) on amphibians in productive recreational fishing lakes of British Columbia

Abstract

Stocking lakes with trout to enhance recreational fishing can negatively affect native aquatic species. Our objectives were (i) to compare presence, relative abundance, body size, and developmental stage of amphibians in lakes with and without rainbow trout (Oncorhynchus mykiss) in British Columbia’s southern interior, and (ii) to estimate the size of trout impact for application to amphibian conservation. Presence of long-toed salamander (Ambystoma macrodactylum), Columbia spotted frog (Rana luteiventris), and Pacific treefrog (Pseudacris regilla) was not significantly different between lake types. In contrast, western toad (Bufo boreas) larvae presence and relative abundance were significantly higher in lakes with trout. Relative abundance of salamander larvae was significantly lower in lakes with trout, but hypothesis testing did not provide consistent evidence of significantly lower abundances of spotted frog and treefrog larvae. However, estimated ratios of relative abundance (impact) indicated that larvae of the salamander and two frogs were ≥65% less abundant in lakes with trout. Salamander larvae were significantly smaller in lakes with trout. Although amphibians may currently coexist with trout in our study region, trout stocking policy in British Columbia should consider amphibian conservation because the presence of trout is associated with lower amphibian abundance and body size in individual lakes.