Operating model has discrete regions

OM uses matrices to model migration

Below is a simplified example of a movement matrix. It shows, for instance, that 50% of tuna will stay in GOM, while 10% will move to each of the CAR, W.ATL, SC. ATL and SE. ATL regions in the modelled timestep (see first row).

GOM CAR W.ATL GSL SC.ATL NC.ATL NE.ATL E.ATL SE.ATL W.MED
GOM 50% 10% 10% 0% 10% 0% 0% 0% 10% 0%
CAR 0 0 0 0 0 0 0 0 0 0
W.ATL 0 0 0 0 0 0 0 0 0 0
GSL 0 0 0 0 0 0 0 0 0 0
SC.ATL 0 0 0 0 0 0 0 0 0 0
NC.ATL 0% 10% 0% 10% 20% 40% 0% 10% 0% 0%
NE.ATL 0 0 0 0 0 0 0 0 0 0
E.ATL 0 0 0 0 0 0 0 0 0 0
SE.ATL 0 0 0 0 0 0 0 0 0 0
W.MED 0% 0% 0% 0% 0% 10% 10% 10% 10% 60%

We can illustrate this matrix by using ‘before’ and ‘after’ maps.

Each of the circles represents 10% of population in a particular region. We visualise movement from three regions at a time, for clarity.

Before migration.

Focusing on populations in GOM, NC. ATL, and W. Med.

After migration.

This is how the movement matrix above predicts that the populations from GOM, NC. ATL, and W. Med will disperse. Because it is difficult to reliably estimate movement matrices, visualising the main steps in migration can enable experts to comment on how plausible these matrices are.