Temporal patterns of forage fish and mesozooplankton in the Columbia River plume

1
Temporal patterns of forage fish and
mesozooplankton in the Columbia River plume

• Amanda Kaltenberg
• Kelly Benoit-Bird
• Robert Emmett
• College of Oceanic and Atmospheric Sciences,
  Oregon State University
• NOAA Fisheries, Northwest Fisheries Science
  Center, Newport, OR

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Project Motivation

• Important ecological interactions
• Juvenile salmon predation determined by forage
  fish abundance because of a dilution effect.
• Seasonal timing of forage fish presence and ocean
  entry of juvenile salmon is important to
  survival.
• More information is needed about the timing of
  presence and temporal variability of forage fish
  presence near the Columbia River plume for
  improved management.

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Project Objectives

• 1. Determine the time lag between the spring
  transition and forage fish presence.
• 2. Characterize the temporal variability of
  forage fish abundance and their prey.
• 3. Determine which oceanographic factors are
  linked with forage fish abundance.

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• Sampling
• March 31 June 27
• - 2 mooring deployments,
• swapped on May 13
• 2 bio-acoustic mooring stations
• - 40 95 m depth
• - forage fish abundance
• - mesozooplankton abundance
• NDBC oceanography mooring
• - SST
• - SSS
• - Wind velocity
• Columbia River flow (USGS Beaver
• Army Terminal, near Quincy, OR)

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Acoustic Moorings

• Bottom-mounted WCP moorings (200-kHz)
• Sampling interval once every 8 seconds, 1 m
  vertical bins

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Data analysis

• Acoustic detections of fish schools dense
  aggregations with discrete edges
• Data were integrated into hourly bins. 40-hour
  running average filter was applied to remove diel
  patterns.

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Spring transition date for 2008
Spring Transition on March 27
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Spring transition date for previous 5 years
15-Mar to 23-May
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Spring transition
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Seasonal timing of fish schools
For schools from the upper 20 m only Fish
schools rapidly increased in June at the deep
site. Highest abundance occurred mid-May at the
shallow site.
--No Data--
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Seasonal timing of fish presence
Multiple linear regression showed the strongest
link between fish was with SST. Surface fish
schools became abundant May 24 after a sharp rise
in SST.
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Upper 20 m Fish abundance does not appear to be
related to zooplankton abundance. Deep site R2
lt 0.01 Shallow site R2 0.05
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April 22
0-
10-
20-
30-
Depth (m)
40-
50-
60-
70-
80-
0000
0600
1200
0000
1800
14
April 23
0-
10-
20-
30-
Depth (m)
40-
50-
60-
70-
80-
0000
0600
1200
0000
1800
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Total water column backscatter Strong peaks early
in the season, with gradual increase later.
--No Data--
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Fish temporal variability

• Multiple linear regression between fish abundance
  and oceanographic variables indicated that fish
  presence was linked to SST anomaly but the
  correlation was opposite at the two sites.
• Inshore/offshore movements of fish
• Spatial difference in oceanography (1
  oceanographic buoy in this study)
• SSS was significantly linked with fish presence
  at deep site only
• Upwelling index had significant link with fish
  presence only at shallow site

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New Questions

• Surface schools didnt become abundant until 2
  months after the spring transition (end of May),
  when temperature was over 11-12C.
• Can we predict the timing of forage fish
  presence?
• Is there a link between fish abundance and
  phytoplankton prey?
• When zooplankton is low, fish forage on
  phytoplankton.
• How does fish species assemblage influence
  patterns?

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Impacts of study

• Acoustic moorings were successful at
  characterizing the temporal abundance patterns
  for both schooling fish and mesozooplankton prey.
  
• High degree of variability.
• Sampling strategies
• Emphasizes importance of timing for salmon
  management

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Acknowledgements

• Funding from Army Corps of Engineers
• Bill Wick Marine Fisheries Award
• COAS Ecology of Marine Nekton Award
• Chad Waluk
• Paul Bently
• M/V Forerunner, F/V Piky