Striped Bass Predation On Juvenile Salmon: Take ‘Em Or Leave ‘Em

In the Sacramento-San Joaquin Delta in California, juvenile Chinook salmon (Oncorhynchus tshawytscha) experience high mortality during their outmigration to sea, and predation by striped bass (Morone saxatilis) is considered significant.  Previous studies show varying consumption of juvenile salmon, and ecological variables likely create localized instances of heightened predation.  My study objectives are to examine how habitat alterations influence striped bass consumption of juvenile salmon and the magnitude of population level impacts of predation at Woodbridge Irrigation District Dam (WIDD).  Principal findings indicate significant differences in important diet items for striped bass caught at WIDD (n=20; % weight: Chinook salmon 93.73%, crayfish 1.48%), and natural areas (n=20; % weight: Chinook salmon 0.0%, crayfish 90.87%).  Below WIDD, I used depletion electrofishing to remove striped bass (average FL 415 mm) that had an average per capita consumption rate of 9.5 and population level impact of 145 salmon consumed per day.  Recapture rates of tagged releases of juvenile salmon increased from 2.5% before and 6.6% after striped bass removal.  It is crucial to determine population level impacts from predation hotspots to assess the relative potential of various management strategies (e.g. predator removal, habitat restoration, etc.) for salmon recovery.