PowerPointPrsentation

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The influence of circulation patterns on the
interaction between Baltic larval cod and
zooplankton as their prey
H.-H. Hinrichsen1, J.O. Schmidt1, C. Möllmann2,
R. Voss1, and A. Lehmann1 1) Leibniz-Institute
of Marine Sciences, Düsternbrooker Weg 20,
D-24105 Kiel, Germany 2) Danish Institute for
Fisheries Research, Charlottenlund Castle,
DK-2920 Charlottenlund,Denmark
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• Aims of the study
• Analyses of intra- and interannual variability of
  drift in the Baltic
• Dependency of food availability for larval cod in
  the Baltic on circulation patterns
• Impact of temporal mismatch between cod larvae as
  predator and copepods as their prey as an impact
  on the spatial availability of food

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Spawning and feeding areas of Baltic cod
Sweden
Gotland Basin
Bornholm Basin
Gdansk Deep
After Bagge et al. 1994
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Particle tracking model and experimental design

• Utilisation of eddy-resolving baroclinic
  circulation model
• individual drifter representing cod larvae
  inserted into simulated current velocity fields
• release locations represent Baltic cod spawning
  area
• release during entire spawning season of cod
  (April to September) every 10 days
• drift duration 60 days (pelagic larval phase)
• time period 1979-1998

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initial retention 1
retention 2
mean dist. gt, variance dist. lt
mean dist. lt, variance dist. lt
dispersal 1
dispersal 2
mean dist. lt, variance dist. gt
mean dist. gt, variance dist. gt
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Mean drift-distance
Km
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Variance of mean drift-distance
Km
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Mean seasonal cycles of copepod abundance in the
Baltic
Deep water area
Shallow water area
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Plankton Prey
Development of copepod species in the Baltic Sea
Main reproduction Spring, Central Basin, deep
water layers
Main reproduction Summer, shallow water areas
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Prey density, size
Swim speed, Reactive area, Turbulence
Individual-Based Model of larval survival
Encounter
Foraging
Growth
Starvation
Predator size, Density, Preference, Availability
of other prey
Avoidance, escape
Predation
modified after Letscher et al. (1996)
Next Day
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Larval Survival
Output of coupled IBM and hydrodynamic model
interannual variability in larval survival in
comparison to observations
R2 0.61 p lt 0.02
Prey field inclusive P. elongatus (1992 no
data) Observed survival through the
larval phase recruitment at age 0 per daily egg
stage III production
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Larval Survival
Spatial variability in larval survival, scenario
without P. elongatus
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From model results to observations
For time period 1966 1988, Anomalies
recruits vs. food availability r2 0.60

• Recruitment of Baltic Cod (Virtual Population
  Analysis)
• Food availability of Pseudocalanus elongatus
  (developmental days x nauplii abundance)

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Calculation of overlap coefficients (1)

Determination of statistical rectangles
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Calculation of overlap coefficients (2)
A and B are the proportions of larvae found in
each rectangle at hatch (A) and after a given
time period of larval drift (B) n is the number
of statistical rectangles Date of peak prey
abundance corresponds to larval occurrence after
larval drift (B)
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Coefficients of overlap after 10 days of larval
drift
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Summary and Conclusions

• Identification of regime shift by simple
  statistical parameters of larval drift
• Transport processes in combination with prey
  availability create temporal and spatial survival
  windows for larvae
• Spatial overlap patterns larvae and their prey
  depend on variation of circulation patterns
  (retention vs. dispersal)
• Variability of larval prey encounter can be
  coupled to variations in the timing of the
  match/mismatch between predator and prey