Fishing out collective memory of migratory schools

Animals form groups for many reasons but there are costs and
benefit associated with group formation. One of the benefits is collective
memory. In groups on the move, social interactions play a crucial
role in the cohesion and the ability to make consensus decisions.
When migrating from spawning to feeding areas fish schools need to
retain a collective memory of the destination site over thousand of
kilometers and changes in group formation or individual preference
can produce sudden changes in migration pathways. We propose a
modelling framework, based on stochastic adaptive networks, that
can reproduce this collective behaviour. We assume that three factors
control group formation and school migration behaviour: the intensity
of social interaction, the relative number of informed individuals
and the preference that each individual has for the particular migration
area. We treat these factors independently and relate the individuals’
preferences to the experience and memory for certain migration
sites. We demonstrate that removal of knowledgable individuals
or alteration of individual preference can produce rapid changes in
group formation and collective behavior. For example, intensive fishing
targeting the migratory species and also their preferred prey can
reduce both terms to a point at which migration to the destination
sites is suddenly stopped. The conceptual approaches represented by
our modelling framework may therefore be able to explain large-scale
changes in fish migration and spatial distribution