Reviews in Fish Biology and Fisheries 11: 255–277, 2002.
© 2002 Kluwer Academic Publishers. Printed in the Netherlands.
Point of view
A general theory on ﬁsh aggregation to ﬂoating objects: An alternative to
the meeting point hypothesis
e A. Santiago & Ana T. Santana-Ortega
Departamento de Biolog´ıa, Univ. de Las Palmas de Gran Canaria, Campus de Taﬁra, Edf. Ciencias B´asicas, Las
Palmas de Gran Canaria, Spain (E-mail: email@example.com)
Accepted 11 June 2002
Abstract page 255
When is a ﬁsh aggregated with an object? (A deﬁnition of aggregation) 256
What are ﬂoating objects? 258
Why do ﬁsh aggregate around ﬂoating objects? 259
Why do ﬁsh associate to ﬂoating objects? 261
Fish species which aggregate/associate under ﬂoats 271
Rhythms of aggregation and association of the ﬁsh fauna 271
Generalization and conclusions 272
Key words: Fish Aggregating Devices, FAD, ﬂoating structures, drifting ﬂotsam, indicator log, meeting point
An immense variety of ﬁsh may, on occasions, aggregate around or be associated with ﬂoating structures
such as drifting algae, jellied zooplankton, whales, ﬂoats or anchored ﬁsh aggregating devices (in effect, there are
over 333 ﬁsh species belonging to 96 families recorded in the literature).
Several hypotheses have been advanced to explain this behaviour of pelagic ﬁsh, although the most widely
accepted theory is that ﬁsh use ﬂoating materials, to some extent, to protect themselves from predators. However,
we think that aggregation under ﬂoats may be the result of behaviour that has evolved to safeguard the survival of
eggs, larvae and juvenile stages, during dispersion to other areas. Natural ﬂoating structures (e.g., algae, branches
of trees) drift in sea currents that originate in places where the ﬂoating objects are frequently found (e.g., river
estuaries, coastal areas). These same sea currents also introduce some of the planktonic production generated in
these areas into the oligotrophic pelagic environment. Fish associated with drifting ﬂoating structures probably feed
on invertebrates associated with the structures. However, they may also beneﬁt from the accumulated plankton
in the converging waters. Adult ﬁsh of some migratory species (tuna, dolphinﬁsh, etc.) have also developed
similar associative behaviour around drifting objects for other reasons (e.g., resting places, presence of bait ﬁsh,
geographical references and school recomposition). In this context, the meeting point hypothesis is only applicable
to one speciﬁc case, the tuna and tuna-like species.
Aggregative and associative behaviour, under and around ﬂoating devices, may be the result of convergent
behaviors that result from different motivations. However, generally this behaviour can be explained by the fact
that drifting ﬂoating objects represent a means of reaching relatively rich areas, where larvae and juvenile ﬁsh have
an increased chance of survival.