Spokane Tribe of Indians

1
Lake Roosevelt Crustacean Zooplankton Temporal
and Spatial Dynamics

• Spokane Tribe of Indians
• Lake Roosevelt Fisheries Evaluation Program
• Ben Scofield
• Limnologist
• November 2007

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Introduction to a reservoir.

• Large Temperate Reservoir
• 33,500 ha Surface Area
• 243 km Length
• 36 m Zmean
• 15 m Mean Drawdown
• 3,000 m3 s-1 Qmean
• 45 d Mean Water Retention Time
• Meso - Oligotrophic Trophic Status

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Study Area
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2005 KOK RBT Diet Ria Values

• Scofield et al. 2007 Daphnia is the single
  largest component of kokanee and rainbow trout
  diets.

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Carbon Sources in Lake Roosevelt

• Black et al. 2003 - Found predominance of
  planktonically fixed C in most organisms.

Even benthically oriented fish such a large scale
suckers, bridgelip suckers, and sculpin had high
of planktonically fixed C
Only periphyton and snails had exclusively
benthically fixed C.
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Presentation Overview

• What is the relative composition for density and
  biomass?
• How do lengths vary across time?
• How does biomass vary across time?
• How does biomass vary across locations?
• How does biomass vary from littoral to pelagic
  sites?
• How does biomass vary vertically in water column?
• What factors influence zooplankton?

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Common Crustacean Zooplankton in Lake Roosevelt
Copepods
Cladocerans
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Relative Density
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Relative Biomass
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Mean Zooplankton Lengths at Index Locations
month?
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Mean Zooplankton Biomass at Index Locations
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Mean Zooplankton Biomass
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66 m tow versus 33 m tow Zooplankton Biomass
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Daphnia Biomass and Chlorophyll a
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Summary

• Copepods (nauplii) contribute the most to
  zooplankton density
• Daphnia (D. pulex) contribute the most to
  zooplankton biomass
• Year round mean daphnia lengths usually are gt 1.0
  mm
• Daphnia biomass peaks in late Jul to early Aug
• Zooplankton biomass generally increases as you
  move downstream and into reservoir arms
• Near-shore zooplankton biomass may be greater
  than at mid channel
• Shallow zooplankton tows yield higher biomass
  than deeper tows
• Mean daphnia length is correlated to water
  retention time