Riparian Management and Fish Productivity

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Riparian Management and Fish Productivity

• Peggy Wilzbach and Ken Cummins
• USGS CA Cooperative Fish Research Unit
• Humboldt State University

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Habitat isnt enough. Fish need food!

• Many streams with pristine habitat support
• low production of salmonid fishes
• Some of the most productive streams have
• suboptimal habitat (but abundant food)
• The greatest salmonid production is realized in
  hatchery channels!

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Options for increasing salmonid production?

• Direct addition of food organisms (not realistic
  over long-term)
• Nutrient or organic matter enrichment
• Increasing autotrophic production

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Case study Effects of riparian canopy opening
and salmon carcass addition on the abundance and
growth of resident salmonids

• Wilzbach, M.A. et al. 2005. Can. J. Fish.
  Aquat. Sci. 62 1-10.

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Experimental Design
buffer
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Lower Klamath River
Lower Smith River
SF Rowdy
Pacific Ocean
Pacific Ocean
Savoy
Little Mill
Peacock
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Savoy Creek closed canopy
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Tarup Ck Open Section
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Incident Radiation Savoy Ck, July 6, 2003
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Stream temperature did not differ between cut and
uncut reaches in these coastal streams
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Total Salmonid Biomass

• Treatment effects
• riparian
• date
• (but not carcasses)

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Specific Growth Rates
Significant treatment effects riparian, date,
riparian carcass
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Conclusions

• Increased light was more effective than carcass
  addition in enhancing salmonid productivity of
  study sites
• Carcass enhancement may fail to increase salmonid
  production in settings where light is limiting or
  other factors prevent its successful use
• Selective trimming of riparian alder should be
  evaluated as a management tool for enhancing
  salmonid production

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Can the food-generating capacity of a stream be
readily assessed?

• Across broad spatial scales, highly productive
  streams are associated with

• moderate temperatures, groundwater inputs
• relatively low vegetative canopy coverage
• hard waters, relatively high concentrations of
  inorganic nutrients

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• Within regions, need to directly measure prey
  availability
• Macroinvertebrate drift more accurately reflects
  prey availability than does the benthos
• The ratio of behavioral to accidental drifters
  may provide a good index of prey availability
  during low flow conditions

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Behavioral drifter predictably available on a
diel basis
Accidental drifter without predictable pattern
of drift entry windfall diet items
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Summer
R2 0.42
Percent of drift mass from behavioral
drifters (ASIN SQRT)
Specific growth rate of salmonids ( day-1)
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In our study, of terrestrial inverts was
negatively related to fish growth
Percent of Terrestrial Invertebrates in Drift
(ASIN SQRT)
R2 0.62
Specific growth rate of salmonids ( day-1)
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Research needs

• to establish the amount, spatial pattern of
  light gain, and riparian composition needed to
  optimize local food supplies - without
  sacrificing beneficial functions of riparian
  vegetation or cumulating temperature loadings
  downstream.

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