Caribbean spiny lobsters show strikingly coordinated queuing behaviour and
resting, outward-facing radial formations, especially during mass migrations
when large numbers cross shelter-poor substrate in daylight. The close
association of individual lobsters during these behaviours could be due to
chance or some benefit of association such as dilution (and associated
selfish-herd effects), group vigilance, cooperative defence, and/or drag
reduction during migration. To infer probable beneficial functions, we
examined the frequency distributions of individuals and groups using a
seven-year set of field data and additional behavioural observations in large
seawater enclosures. Group size distributions were not significantly
aggregated in dens during the non-migratory period but became highly
aggregated during migration. The group size distributions of lobsters
initially leaving dens and those observed moving in the open were
statistically different from one another, indicating that group sizes at each
of these steps in the migration are not simply the result of previous group
sizes. The distribution of group sizes suggests that, during movement in the
open, dilution, vigilance, cooperative defence, and/or drag reduction may
all favour the formation of queues. During resting in the open, dilution,
vigilance, and cooperative defence may continue to favour individuals that
remain in formation within the group.
Machine Learning Data Imputation and Prediction of Foraging Group Size in a Kleptoparasitic Spider