Hands on session: Evolving migration pattern and distribution of a fish under climate change

1
Hands on sessionEvolving migration pattern and
distribution of a fish under climate change
Geir Huse
CLIMECO meeting Brest, 21-24 April
2
Northeast distribution in warm years
Southwest distribution in cold years
From Ozhigin Luka 1985, Vilhjalmsson 1997
3
Objective

• Hands on session is based on model recently
  presented in
• Huse Ellingsen 2008. Capelin migrations and
  climate change a modelling analysis. Climatic
  Change 87 177-191
• Investigate how global warming might affect
  capelin distribution/migration using an
  individual-based model with artificial evolution
  of life history strategies and movement behaviour

4
Model domain and forcing

• The model area consists of a lattice of 90 by 100
  squares of 20 km sides
• Fields for temperature, currents and plankton
  biomass were taken from bio-physical model
  simulations for the Barents Sea (Ellingsen, al
  2008)

5
Bio-physical simulations
Primary production
Fraction of water warmer than 1C
Ice covered area
6
Mean current fields at 50m and polar front
Year 2000
Year 2047
7
The capelin model

• The entire life span of capelin is simulated
  including egg stage, larval drift, and adult
  drift and movement
• The capelin IBM relies on the state variables
  weight, age, energy density and position.
• The capelin model involved growth, mortality,
  movement and reproduction
• Adaptive traits on strategy vector
• Artificial Neural Network weights
• Spawning date

8
The capelin model Growth

• For the larval fish, growth was calculated using
  temperature, plankton and fish size dependent
  equations for the similar herring larvae (Fiksen
  and Folkvord, 1999)
• For the one year and older capelin, growth was
  calculated using a bioenergetics model (Hewett
  and Johnson, 1992) dependent on temperature, prey
  biomass, fish size and activity level

9
The capelin model Mortality

• Larval mortality was calculated as a function of
  size and visual predation (Fiksen, et al., 2002).
  
• For the older capelin, mortality was inflicted
  though visual predation from cod and marine
  mammals, and starvation.
• Predation risk from cod was assumed to be
  proportional to temperature
• Marine mammal predation was implemented with a
  uniform predation risk
• Starvation is imposed for low energy density
• Mature super-individuals are terminated after
  spawning.

10
Movement and reproduction

• The larvae is drifting
• The adults move actively using the ANN, and are
  also transported by the currents

11
Spawning

• Capelin is known to spawn near shore
• All squares next to shore were allowed spawning
  areas

• Reproduction
• Individualgt 4 years
• Date ?30 days of spawning date
• If so a batch of eggs proportional to body length
  and energy level is laid

12
Scenarios

• Three situations can be contrasted
• Cold climate (year 1996)
• Warm climate (year 2046)
• Alternating cold and warm climate (year 1996 and
  2046 chosen randomly)

Fraction of water warmer than 1C
13
Simulation experiments

• Perform simulations adapting the capelin to cold
  and warm years respectively.
• Perform simulation adapting the capelin with
  alternating warm and cold years.
• Investigate the effects of increasing or reducing
  predator abundance
• Change codnum parameter in td subroutine for
  example to 1E9 or 1E7
• Investigate the effect of reducing capelin
  density dependence
• Increase car parameter in parfile.txt to 0.5
• Increase mutation rate
• Increase mute parameter in parfile.txt to 0.2