  We analyse the dynamics of fishing vessels with different home ports in an
area where these vessels, in choosing where to fish, are influenced by their
own experience in the past and by their current observation of the locations of
other vessels in the fleet. Empirical data from the boats near Ancona and
Pescara shows stylized statistical properties that are reminiscent of Kirman
and F\"ollmer's ant recruitment model, although with two ant colonies
represented by the two ports. From the point of view of a fisherman, the two
fishing areas are not equally attractive, and he tends to prefer the one closer
to where he is based. This piece of evidence led us to extend the original ants
model to a situation with two asymmetric zones and finite resources. We show
that, in the mean-field regime, our model exhibits the same properties as the
empirical data. We obtain a phase diagram that separates high and low herding
regimes, but also fish population extinction. Our analysis has interesting
policy implications for the ecology of fishing areas. It also suggests that
herding behaviour here, just as in financial markets, will lead to significant
fluctuations in the amount of fish landed, as the boat concentration on one
area at a given point in time will diminish the overall catch, such loss not
being compensated by the reproduction of fish in the other area. In other
terms, individually rational behaviour will not lead to collectively optimal
results.
