Diet composition in San Francisco Estuary striped bass: does trophic adaptability have its limits? |
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Authors: | Matthew L Nobriga Frederick Feyrer |
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Institution: | (1) CALFED Science Program, 650 Capitol Mall, 5th Floor, Sacramento, CA 95814, USA;(2) California Department of Water Resources, 901 P Street, 4th Floor, Sacramento, CA 95814, USA |
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Abstract: | Trophic adaptability is a term used to describe feeding flexibility in fishes. Though a useful conceptual starting point,
fishes often face constraints on their ability to switch prey that could limit feeding success even when prey switching is
observed. We compared striped bass diet compositions summarized from previously published studies in California’s Sacramento-San
Joaquin Delta during two time periods (1963–1964 and 2001–2003), which allowed us to evaluate trophic adaptability in San
Francisco Estuary striped bass at multiple time scales, ranging from intra-annual to multidecadal. The Delta is the landward
region of the San Francisco Estuary; over time between the study periods, the Delta underwent substantial changes in potential
prey availability for striped bass. We found evidence for trophic adaptability in San Francisco Estuary (SFE) striped bass
at all temporal scales examined. Despite this ability to adapt to changes in prey availability, the relative abundance and
carrying capacity of young striped bass have declined. This decline has previously been associated with substantial declines
in their dominant historical prey—mysid shrimp. Our results, coupled with these previous findings, indicate that trophic adaptability
may have limited usefulness as a conceptual model to predict foraging success when other food web constraints are not considered.
We speculate that this is particularly true in highly invaded ecosystems like the San Francisco Estuary because invading species
often introduce substantial and permanent changes into food webs, decreasing the likelihood that a predator will find prey
assemblages that fully replace historical prey assemblages. |
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Keywords: | Striped bass Morone saxatilis Diet composition Trophic adaptability Invasive species San Francisco Estuary |
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