Stream hydrology and a pulse subsidy shape patterns of fish foraging

Pulsed subsidy events create ephemeral fluxes of hyper-abundant resources that can shape annual patterns of consumption and growth for recipient consumers. However, environmental conditions strongly affect local resource availability for much of the year, and can heavily impact consumer foraging and growth patterns prior to pulsed subsidy events. Thus, a consumer’s capacity to exploit pulse subsidy resources may be influenced by antecedent environmental conditions, but this has rarely been shown in nature and is unknown in aquatic ecosystems. We sampled fish at a high frequency (daily - weekly measurements) to examine the importance of hydrologic variation and a salmon pulse subsidy on the foraging patterns of two stream fishes in a coastal southeast Alaska drainage. We then explored effects of inter annual hydrologic variation on Coho Salmon growth trajectories and sequential access to pulse subsidy resources (i.e., whether fish exceeded an egg consumption gape limit) in a bioenergetic simulation. These data were used to investigating the relative importance of streamflow and salmon spawning on the foraging patterns of two stream salmonids.