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Riparian Management and Fish Productivity

Riparian Management and Fish Productivity. Peggy Wilzbach and Ken Cummins USGS CA Cooperative Fish Research Unit Humboldt State University. Habitat isn’t enough. Fish need food!. Many streams with pristine habitat support low production of salmonid fishes

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Riparian Management and Fish Productivity

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  1. Riparian Management and Fish Productivity Peggy Wilzbach and Ken Cummins USGS CA Cooperative Fish Research Unit Humboldt State University

  2. Habitat isn’t 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!

  3. Options for increasing salmonid production? • Direct addition of food organisms (not realistic over long-term) • Nutrient or organic matter enrichment • Increasing autotrophic production

  4. 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.

  5. Experimental Design buffer

  6. N Tarup 0 5 10 15 kilometers Tectah Lower Klamath River Lower Smith River SF Rowdy Pacific Ocean Pacific Ocean Savoy Little Mill Peacock

  7. Savoy Creek: closed canopy

  8. Tarup Ck– Open Section

  9. Incident Radiation: Savoy Ck, July 6, 2003

  10. Stream temperature did not differ between cut and uncut reaches in these coastal streams

  11. Total Salmonid Biomass • Treatment effects: • riparian • date (but not carcasses)

  12. Specific Growth Rates Significant treatment effects: riparian, date, riparian* carcass

  13. 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

  14. 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

  15. 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

  16. Behavioral drifter: predictably available on a diel basis Accidental drifter: without predictable pattern of drift entry; “windfall” diet items

  17. Summer R2 = 0.42 Percent of drift mass from behavioral drifters (ASIN SQRT) Specific growth rate of salmonids (% · day-1)

  18. 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)

  19. 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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