The following article has just been published in MEPS:
Piroddi, C., Bearzi, G., Christensen, V. 2011. Marine open cage aquaculture in the eastern Mediterranean Sea: a new trophic resource for bottlenose dolphins.
ABSTRACT: Over the last 2 decades marine open cage aquaculture in the Mediterranean Sea has
grown rapidly, leading to increased productivity in the water column near fish farms. Here we
investigated the effect of such increase in productivity on the common bottlenose dolphin Tursiops
truncatus. We developed an ecosystem model for the inner Ionian Sea Archipelago, western
Greece, to: (1) evaluate the trophic interactions between bottlenose dolphins and their surrounding
ecosystem, including
cage-associated organisms; (2) investigate simultaneously 3 hypotheses
that could explain bottlenose dolphin dynamics: (a) increasing fishing effort and changes in ocean
productivity, (b) competition with other species, and (c) increase in number of fish farms; and
(3) explore spatial trends in bottlenose dolphins distribution using the increased number of fish
farms as an explanatory variable. Comparisons of model predictions with historical time-series
data indicate that only the increase in number of cages and thereby in productivity near fish farms
contributed to the trends observed in dolphin numbers. Spatial analysis also confirmed an
increase in occurrence of these dolphins in the proximity of the farms. These outcomes suggest
that high productivity in waters surrounding fish cages—within a coastal area that is markedly
oligotrophic—may attract bottlenose dolphins. The present study shows that open cage
aquaculture
has benefited bottlenose dolphins by easing their way of catching prey. Further studies
should be conducted in other areas of the Mediterranean Sea to investigate whether the higher
occurrence of bottlenose dolphins around fish cages is a common pattern and if it is driven by the
trophic status of the ecosystem or by the type of fishes that surround the cages.
KEY WORDS: Bottlenose dolphin · Fish farms · Ionian Sea · Ecosystem modelling approach