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Sarà et al: Dispersal of fish farm waste
ferences were not observed in sediments, which in the
absence of anthropogenic inputs were similar in com-
position among sites positioned 500 m apart. Thus, by
only studying variability in the water column, the
extrapolation of information on the effect of fish farm
waste on the marine environment (and perhaps on
other impacted aquatic systems) might be biased; sed-
iments may often provide more reliable interpreta-
tions.
CONCLUSIONS
We detected some effects of organic loading from
fish farm waste on the surrounding environment at dis-
tances up to 1000 m from the cages under variable
environmental conditions. Nevertheless, we did not
detect any ‘impact’ that implied biological conse-
quences and environmental costs. Since we analysed a
chronic impact at each location (off-shore fish farming
is not seasonal), it is likely that organic enrichments
observed at different distances may lead to structural
rearrangements of benthic assemblages. However, we
only detected a deviation from natural organic enrich-
ment. Pitta et al. (1999) stressed the need for reconsid-
eration of the ‘impact’ concept and spatial influence in
future investigations. Vivificated oligotrophic waters
from our study locations seemed to be able to accom-
modate organic waste (more than 40 to 50 tons) origi-
nating from fish farms, converting it into fresh biomass
and still maintaining the system under the impact
threshold.
Therefore, researchers should reconsider the role of
the effects from offshore fish farms according to the
following points: (1) the relative area of influence of
the impacts of fish farms seems to proportionally in-
crease with increasing current velocities; (2) the water
column appears to be an ‘aleatory’ mirror of the trophic
situation, whereas sediments appear to mirror the real
dispersion; and lastly (3) the distribution of waste from
the cages seems to be dependent on movements at
the bottom of the water column, which confirms the
recently identified role played by resuspension move-
ments (Cromey et al. 2002).
Acknowledgements. This work was funded by the Parco
Scientifico e Tecnologico della Sicilia, the Ministero Politiche
Agricole e Forestali (MiPAF, Italy) and the Ministero
dell’Istruzione, dell’Università e della Ricerca (MIUR, Italy).
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