Stream hydrology and a pulse subsidy shape patterns of fish foraging

Area of Science:

• Ecology
• Aquatic Ecosystems
• Fisheries Science

Background:

• Pulsed subsidy events provide abundant resources, influencing consumer dynamics.
• Environmental conditions significantly impact consumer foraging and growth before these events.
• The influence of antecedent conditions on exploiting pulsed subsidies is poorly understood in aquatic systems.

Purpose of the Study:

• To investigate the role of hydrologic variation and salmon pulse subsidies on stream salmonid foraging and growth.
• To determine how antecedent environmental conditions affect the exploitation of pulsed resources by fish.

Main Methods:

• High-frequency sampling of fish stomach contents (daily-weekly).
• Analysis of fish consumption rates relative to streamflow and resource availability.
• Bioenergetic simulations to assess interannual hydrologic variation effects on growth.

Main Results:

• Dolly Varden and Coho Salmon exhibited nonlinear flow-foraging relationships pre-spawning, with peak consumption at baseflow and high flows.
• Macroinvertebrates were primary forage before spawning; salmon eggs dominated post-spawning.
• Post-spawning, consumption increased and was flow-independent.
• Hydrologic variation influenced Coho Salmon growth trajectories.

Conclusions:

• Antecedent hydrologic conditions are critical for juvenile salmonids to reach a size capable of consuming salmon eggs.
• Access to marine pulse subsidies by stream salmonids is contingent on prior growth influenced by water flow.
• Understanding flow-foraging relationships is key to predicting resource pulse utilization.