Circulation and trophodynamic modeling of larval fish populations: a case study of Georges Bank cod

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Circulation and trophodynamic modeling of larval
fish populations a case study of Georges Bank cod

• Cisco Werner
• Marine Sciences Department
• U of North Carolina at Chapel Hill
• cisco_at_unc.edu

Supported by NSF and NOAA
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Colleagues

• Canadian DFO Ian Perry, Fred Page, Charles
  Hannah, Mike Sinclair, Dave Greenberg, John
  Loder
• Dartmouth College Dan Lynch, Chris Naimie
• NMFS Greg Lough, Larry Buckley, Jim Manning
• UNC-CH Brian Blanton, John Quinlan

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Outline

• Physical-biological coupling in marine ecosystems
• GLOBEC and Georges Bank
• Key physical processes on GB
• Modeling retention
• Trophodynamics and IBMs
• Next steps and Conclusions

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GBank
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GBank
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GBank
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Cod fluctuations
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Phases of Georges Bank GLOBEC

• Onset of stratification (1995)
• Exchange (1997)
• Fronts (1999)
• Synthesis Integration (2002-06)
• Broadscale Cruises (1995-1999)

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U.S. Cruises Canadian Cruises
Year Cruises Days Cruises Days
______________________________________________
1993 1 6 1994 8 82 1 7
1995 23 272 2 18 1996 11 115 1 8
1997 23 252 1 8 1998 12 122 1999
27 331 4 3 Totals 104 1,174 10 77
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Physical forcing and flow features- tides-
winds- heating-cooling
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Finite Element Mesh Georges Bank /
Northwest Atlantic Model
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Model equations
Quoddy

• Nonlinear prognostic, finite element model
  (Lynch Werner,1991)
• 3-D shallow water equations

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• Higher order turbulent closure

• wherein
• E1 and B1 are experimental constants (Mellor
  Yamada, 82)
• W is a wall proximity function (Blumberg et al.
  1992)
• and the vertical turbulent mixing coefficients
• (Nm,Nh,Nq) (qlsm,qlsh,qlsq)
• are given in terms of the stability functions
  sm,sh and sq as in Galperin et al. (1988)

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Tidal ellipses Residual
(time-averaged) currents
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Wind
Wind effects
10 meters
1 meter
Decreased wind effects
50 meters
30 meters
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Retention/Loss from Advective effects only
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Spawning, circulation and retention (Page et al.
1999)
Sept-Oct
March-April
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Larval behavior
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Model generated larval behavior
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What about feeding?
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Individual level
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Hydrodynamics and Individual Based Modeling
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Turbulence distribution on Georges Bank
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Basic growth flowchart
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Larval Age Larval Size Larval Behavior
Start x0,y0,z0,t0
Yolk ?
Yolk Sac Contribution
Y
N
Encounter Rate
Successful Pursuit
Y
Light ?
Prey Biomass Encountered
Prey Conc Prey Type
Larval Size
Light Level Turbulence Temperature
Y
Next Time Step
Reduce Prey Biomass
Satiated ?
Advect, Behave xt,yt,zt,tt
N
Metabolic Costs
Consume Prey
Growth Length,Weight
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• on-bank retention
• advective losses
• starvation
• growth
• distribution

Surviving larvae are located at depth in
retentive regions!!
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Examine growth of cod larvae during 95 98
3D Representations of observed prey and
temperature fields modeled turbulence and light
fields
Will produce 3D maps of potential growth
zones. Can this technique be used to define
regions of high and low growth or survivorship?
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Oithona Naups
Oithona Copes

• March 1995
• Objective analysis
• of zooplankton biomass on Georges Bank from
  broadscale MOCNESS sampling.

01m
10m
20m
40m
60m
?g/liter
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March Temp
May Temp

• March 1995
• Objective Analysis
• of temperature
• on Georges Bank
• from Broadscale CTD
• sampling.

01m
10m
20m
40m
60m
C
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12mm May
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Interannual variability of larval growth may be
related to zooplankton abundance
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Modeling zooplankton dynamics (Calanus fin.)
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How to couple larval fish models and zooplankton
models?
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Predators?
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What about links to basin-scales?
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Fish and apex predators which depend directly on
the target taxa
Cod, haddock, herring, capelin, baleen whales
Cod, haddock, herring, salmon capelin, baleen
whales
Cod, haddock, herring, redfish, salmon,
baleen whales
Cod, haddock, herring, salmon mackerel, blue
whiting, baleen whales
Cod, haddock, whiting, herring,
mackerel, sandeel, pout
Cod, haddock, herring, capelin, baleen whales
Cod, haddock, herring, mackerel, sandlance, baleen
whales
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NW Atlantic cod
North Sea cod
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B. Dickson
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Gulf of Maine/Georges Bank Region
A hydrographic and faunal transition zone
especially vulnerable to changes in climate.
C. Greene
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Circulation Increased Labrador
Current Transport
NAO (-)
NAO ()
(Drinkwater et al., 2001)
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Advance of Labrador Slope Water in 1997-1998
(Drinkwater et al., 2001)
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C. finmarchicus in the northern North Sea, and
the North Atlantic Oscillation
As reported by Fromentin and Planque, 1996
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Calanus abundance map compiled from data supplied
by SAHFOS to NERC Marine Productivity project
GR2/2749 and data from the EU-TASC project
1950-1999 mean abundance
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NORTH ATLANTIC OCEAN
SHELF SEAS
Climate forcing of ocean circulation
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Conclusions

• Physical models are capable of providing
  realistic flow fields on appropriate space-time
  scales
• Feeding environment/trophodynamics can provide
  insight into key processes and their location
  w/IBMs
• Interannual variability, coupling to
  basin-scales, predators, etc. still missing