Differential Incorporation of Natural Spawners vs. Artificially Planted Salmon Carcasses in a Stream Food Web: Evidence from delta super(15)N of Juvenile Coho Salmon

摘要

Placement of salmon carcasses is a common restoration technique in Oregon and Washington streams, with the goal of improving food resources and productivity of juvenile salmon. To explore the effectiveness of this restoration technique, we measured the delta super(15)N of juvenile coho salmon (Oncorhynchus kisutch) as an index of the incorporation of salmon-derived nutrients (SDN) in streams with varying amounts of natural spawners and artificially placed carcasses. Although delta super(15)N of juvenile coho salmon increased with salmon carcass mass in the stream channel, this relationship was only significant for natural spawners. Artificially placed carcasses did not appear to increase SDN utilization by juvenile coho salmon. Possible explanatory factors include the restricted spatial and temporal distribution of carcasses, general absence of eggs, and lack of substrate bioturbation associated with artificially placed carcasses. Our study suggests that artificially placed carcasses at the levels added in the Oregon Coast Range may not directly mimic the role of natural spawners in stream foodwebs.