THE SPAWNING STRATEGY OF ANCHOVIES IN THE BAY OF BISCAY

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THE SPAWNING STRATEGY OF ANCHOVIES IN THE BAY OF
BISCAY

• Agurtzane Urtizberea
• Supervisor
  Øyvind Fiksen
• 
  Co-Supervisor Arild Folkvord
• 
  Advisor Xabier Irigoien

HERRAMIENTAS
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GEOGRAPHICAL LOCATION

• The Bay of Biscay
• Part of the eastern North Atlantic
• surrounded by the FrenchSpanish coast

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ANCHOVY (Engraulis encrasicolus) LARVAES
DISTRIBUTION

• The spawning time is from March to June and the
  main spawning areas are Gironde river plume,
  Adour river plume and some areas of the shelf
  break.
• The highest early larvae concentration in the
  spawning area, around river plumes.
• The average size increase with direction off the
  shelf.
• Small larvae is found in the river plume
• and larger ones off the shelf. This suggests a
  drift.

Irigoien X. et al 2007
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JUVENILES SPATIAL DISTRIBUTION
Juveniles
J F M A M J J A S O
N D
Larger juveniles are on the shelf and the
smallest off the shelf. Contrary to the larvae.
Transport cycle hypothesis
Irigoien X. et al 2007
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FOOD AND PREDATORS SPATIAL DISTRIBUTIONS

• The plankton concentration is higher on the shelf
  than off the shelf.
• There isnt too much difference of the large
  zooplankton concentration on the shelf and out
  off the shelf.
• Less predators off the shelf
• than on the shelf.

Irigoien X. et al 2007
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LOOPHOLE HYPOTHESIS

• A significant part of the larvae is
• advected off the shelf due to the north
• eastern winds.
• The Autumn North West Winds can help to bring
  back the juveniles to the shelf.
• In Spring they return to the nursery areas.
• The spatio-temporal loophole hypothesis suggests
  that the larvae, which are drifted off the shelf,
  benefit themselves of the low predatory
  pressure. Afterwards, the juveniles are less
  susceptible to predation and return to the shelf.
  

Irigoien X. et al 2007
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HOW TO EVALUATE THE LOOPHOLE HYPOTHESIS

• Engraulis encrasicolus no laboratory experiment
  engraulis mordax
• Southern California Bight
• INDIVIDUAL BASED MODEL for anchovy larvae with
• a behaviour model vertical migration, swimming
  speed, turning rate (Vlymen W.J. 1977, Hunter
  J.R. 1972)
• a feeding process.
• a physiological model.

• INDIVIDUAL BASED MODEL GENERALIZED CIRCULATION
  MODEL with
• characteristics of the environment of the Bay of
  Biscay ( water temperature, turbidity, ...).
• prey and predator spatial distributions.

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THE FEEDING PROCESS

• The feeding process is a predator-prey
  interaction and will be modeled for larvae using
  the encounter rate, succesful approach and the
  capture success (Fiksen Ø. and Mackenzie B.R.
  2002).
• The encounter rate depends on light, turbulence
  and preys characteristics such as size, contrast
  and locomotion.
• Succesful approach is to get close enough to
  attack the prey without getting to escape. This
  distance depends on the probability of being
  detected and predators capability for a
  succesful capture.
• Capture success depends on the strike distance,
  prey escape direction and the relatives
  velocities of attack and escape between the
  predator and prey.

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PHYSIOLOGICAL MODEL
Theilacker G.H. 1987, Methot R.D. et al. 1979
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PREY DISTRIBUTION IN THE BoB
Size spectra the number of
prey for each size.
NBNormalized biomas bs biomass size
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• QUESTIONS

• IBMGCM Recruitment
• How affect the environment in the recruitment
  process?
• Who are the survivors?

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THANK YOU FOR YOUR ATTENTION!
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GENERAL CIRCULATION PATTERN IN THE BAY OF
BISCAY

• Is possible for the juveniles that are transport
  off the shelf to come back to the shelf in the
  same year?
• In winter the southward component of
• wind is relaxed then it allows to develop an
  eastward surface current off the Iberian
  Peninsula.
• The slope water can be collected into eddies.
  These eddies trap and transport biological
  material from the shelf and slope.

Irigoien X. et al submitted
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SPAWNING TIME AND AREA OF THE ANCHOVY
Engraulis encrasicolus

• The main spawning areas
• -Gironde river plume
• -Adour river plume
• -Some areas of the shelf break.

Irigoien X. et al 2007
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Phytoplankton
Zooplankton
Fish
Light
Hypothesis Eiane et al. (1999) Reduction of the
abundance of visual predators could be a reason
to the increase of tactile predators
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