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Introduction
SEPODYM is a 2D coupled physical-biological interaction model at the scale of
ocean basin, combining a forage (prey) production model with an age structured
population model of targeted (tuna predator) species. The model contains
multi-gear and one or multi-species, with environmental and spatial components
used to constrain the movement and the recruitment of tuna. All the spatial
dynamic modelling of SEPODYM is based on diffusion–advection-reaction
equations in two horizontal dimensions.
The use of diffusion models for simulating random dispersion of animal
population is not recent and different applications are discussed in the
literature (e.g., Skellam 1973; Okubo 1980; Okubo 1986; Murray 1993); however,
in some cases animal populations show directional movement. To account for this
behaviour, Okubo (1980; Okubo 1986) presented a derivation of the
advection-diffusion equation, in which directional movements are described by
the advective term of the equation.
An extension of this approach has been used for the analysis of tagged tuna
movement (Sibert et al. 1999), and the treatment of the spatial dynamic
component in SEPODYM uses the same mathematical formulation, except that the
advective terms applied to this equation are different according to the
simulated movements.
For the movement of small forage organisms and tuna larvae and juveniles, the
advective components in the two horizontal dimensions are oceanic currents, but
are habitat index gradients for adult tuna. The equations of transport in the
two horizontal dimensions for forage and tuna populations are given in (Bertignac et al.
1998) and (Lehodey et al. 1998). The habitat index is a function of
forage density, and sea sea temperature . Sea surface temperature, oceanic
currents, and primary production are also used in the model to delineate tuna
spawning areas, transport larvae and juveniles, and simulate the tuna forage
distribution (Lehodey 2001).
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Modeling
the Nutrient – Phytoplankton – Zooplankton Food Web
Modeling tuna forage
Tuna
habitat
Modeling
tuna population
Tuna
Fisheries described in SEPODYM
Results
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