Time-delayed subsidies: interspecies population effects in salmon

Area of Science:

• Ecology
• Aquatic Ecosystems
• Nutrient Cycling

Background:

• Nutrient-poor freshwater ecosystems benefit from cross-boundary nutrient inputs.
• Pacific salmon (Oncorhynchus spp.) transport marine-derived nutrients into freshwater systems via eggs, excretion, and carcasses.

Purpose of the Study:

• To investigate if nutrients from one generation of salmon can positively impact juvenile salmon of subsequent generations.
• To determine the influence of marine-derived nutrients on salmonid population dynamics in freshwater.

Main Methods:

• Studied 12 streams on the central coast of British Columbia.
• Correlated juvenile coho salmon abundance with previous years' adult pink and chum salmon populations.
• Assessed the role of watershed size and other physical stream characteristics.

Main Results:

• Juvenile coho salmon abundance showed the strongest correlation with the abundance of adult pink salmon from previous years.
• Adult chum salmon and watershed size played a secondary role in juvenile coho abundance.
• The positive influence of spawning salmon subsidies on stream productivity is time-delayed and indirect.

Conclusions:

• Naturally occurring spawning salmon subsidies have a significant, positive, time-delayed impact on salmon-bearing stream productivity.
• This is the first study to examine the effects of natural spawning salmon nutrient inputs on the juvenile populations of other salmon species.