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Jeff Schaeffer, Gary Curtis, Ray Argyle |
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USGS Great Lakes Science Center, |
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Ann Arbor, MI. |
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• What prey species are present? |
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• What species are eaten? |
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Can we see effects of predation? |
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Prey availability may depend on age-0 fish |
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Year class strength |
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Good year: small prey |
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Poor year: few prey |
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Growth may be important |
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Affects prey biomass |
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overwinter survival |
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Size-selective predation |
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May no longer be a resource for large predators |
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Too rare |
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Very few large fish |
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Scarcity may increase pressure on alewife |
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Major changes in the food web |
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Total planktivore biomass decreasing |
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Decline in bloater not due to predation |
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Declines in R. smelt and alewife consistent |
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with predation, but growth may be important |
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Prey size structure declining |
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Few large alewife or rainbow smelt |
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Trends are consistent with predation |
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May be difficult to attain (numbers) |
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Food Web changes |
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Predator demand high |
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Pelagic planktivores declining |
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Other 0bjectives may be enhanced |
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Greater proportion of native species in biomass |
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Reduced interactions with exotics |
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New approaches now possible |
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Notes