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Scott F. Collins, PhD
Illinois Natural History Survey
Kaskaskia Biological Station

Tracking the direct and propagating effects of fish production: Experimental insights from too few salmon and too many Asian Carp

Human activities such as habitat degradation and species introductions can greatly affect aquatic food webs when natural ecological processes are disrupted.  For fishes such as Pacific salmon, dams and overharvest have reduced or completely eliminated returns of spawning adults in the Pacific Northwest, along with the marine-derived subsidies they deliver. These annual subsidies are important for stimulating the productivity of numerous aquatic organisms including stream fishes.  Species introductions also pose substantial threats to aquatic ecosystems.  Numbers of invasive Asian carp have increased substantially in recent decades. These fishes are voracious consumers of planktonic resources, raising concerns about their impacts on food webs within invaded ranges, and in the nearby Great Lakes ecosystem. These pressing fisheries issues are a tale of too few and too many.  My colleagues and I have conducted manipulative experiments to unravel the complex pathways through which alterations to fish productivity directly influence food webs, and tracked the propagating responses across ecosystem boundaries into terrestrial environments. These experiments highlight that subsidized and invasive fishes consumptive and exploitative effects on prey populations can directly alter the flux of materials across ecosystem boundaries and can indirectly alter the activity and abundance of terrestrial riparian consumers. Collectively, these experiments indicate that fish populations are an integral thread in the fabric of aquatic-terrestrial food webs.