Balancing Potentially Conflicting Demands: Fish and Frogs in Regulated Rivers
Management of regulated rivers for yellow-legged frogs and salmonids exemplifies potential conflicts among species adapted to different parts of the natural flow and temperature regimes. The frogs oviposit (lay eggs) in rivers in spring and depend on declining flows and warming temperatures for egg and tadpole survival and growth, while river management for salmonids can include high spring flows and low-temperature reservoir releases. Forest Service researchers built a spatially explicit model of how flow and temperature affect frog breeding success. Its mechanisms include adults selecting oviposition sites to balance risks of egg dewatering by decreasing flow versus scouring by high-flow, temperature effects on development, habitat selection by tadpoles, and mortality via dewatering and scouring. In simulations of a regulated river managed primarily for salmonids, below-natural temperatures delayed tadpole metamorphosis, which can reduce overwinter survival. Mitigating this impact via warmer reservoir releases was predicted to cause adults to oviposit before spring flow releases for salmonids, which destroyed the eggs. The relative timing of frog oviposition and high-flow releases appears critical in determining and resolving conflicts between management strategies for salmonid fish and stream breeding frogs. The demonstrated ability of the frog model to evaluate the effect of habitat structure and physical regimes on breeding success has already led to its application to additional sites.?
Forest Service Partners