We investigated the patterns of occurrence of FAD-associated fish off the
coast of Sardinia, Sicily and Majorca (Western Mediterranean). Two working
hypotheses are presented to test whether or not “differences exist in fish
assemblages at i) the spatial and ii) the temporal level”. Quantitative and
qualitative experimental data were obtained from a total of 521 censuses at
17 fish aggregation devices (FAD) using underwater visual observations
carried out in Sardinia and Sicily in May-October 2001 and 2002 and a purse
seine data set on 3 FADs obtained from a previous investigation carried out
in Majorca. The results from the multivariate analysis rejected both
hypotheses. In all locations, patterns of fish assemblages were dominated by
Coryphaena hippurus, Naucrates ductor, Seriola dumerili, Balistes carolinensis and Trachurus spp., a pattern evident from examining data at bi-monthly intervals.
When the most dominant species highlighted with similarity percentage
(SIMPER) analysis were analysed with an analysis of variance (ANOVA), a time
effect was clearly apparent and subsequently confirmed for four of these
five species (B. carolinensis being the exception); the location factor was also found to be relevant (except for the genus Trachurus). We concluded that differences noted were
principally due to the “time shift” in the occurrence of these species in
the three locations, leading to the assumption that a relationship did exist
between the gradual but significant shift in seasonal temperature and
colonization at the study locations. Defining selected community structure
indices was also important because no reference points are actually
available for the pelagic environment in the Mediterranean Sea.