Environmental Engineering Reference
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Fig. 20.3 Gridded geographical distribution of the percentage of the total population of settled
juvenile cod per grid cell at the end of the simulations, summed over the model domain, for the
baseline run (a) and absolute differences between alternative runs and the baseline (b-f); (b) run
with mortality; (c) run with horizontal diffusion with 100 particles per start location; (d) run with a
Gaussian particle release (spawning) pattern; (e) run with an “ontogenetic” (see text) vertical
migration behaviour pattern; and (f) run with a complex (see text) settlement rule
between runs without and with horizontal diffusion while, at the relatively coarse
grid scale used to illustrate these results, the effect of number of particles is hardly
noticeable and only the case of 100 particles per start position is presented
(Fig. 20.3c ). At finer gridding resolution (results not shown), the differences
between 10 and 50 particles are more obvious, suggesting that the appropriate
number of particles per start position should be somewhere between 50 and 100.
This is supported by the pattern of change in MAE values (0.0787, 0.0755 and
0.0759 for differences between runs with 10, 50 and 100 particles and the baseline,
respectively).
20.3.3 Particle Release Patterns
The particle release pattern corresponded with the daily proportion of the annual egg
production (represented by a Gaussian curve) at each spawning location, compared to
the baseline where all particles were released on the sub-population-specific peak
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