Site selection and carrying capacity in Mediterranean ... - FAO Sipam

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countries have used fish sticks originating from the Western Mediterranean. Studies of cultured sea
bass have shown adequate levels of genetic variation within cultivated stocks (Youngson et al. 2001),
However, there is increasing interest in the development of selective breeding programmes for sea
bream and sea bass in order to improve the production of these cultivated species, which makes
necessary further research and the adoption of precautionary measures to better protect wild fish
stocks.
5.2.5 Marine birds and mammals
Wherever fish farms are present in the natural environment, an interaction between aquaculture and
wild life is expected to occur. Selection of appropriate sites can avoid conflicts with wild life, which
in places may include protected species. For example, if the fish farms are located near natural
habitats of marine birds (e.g. coastal wetlands), the negative interaction between bids and aquaculture
can be elevated, as is happening with the cormorant (Phalacrocorax carbo) in south-eastern Spain
(Alamo, 2009). Marine birds use aquaculture facilities as resting areas and feeding grounds, very
often attacking the cultivated species on which they attempt to feed. Farmers use much time and
resources to try to avoid fish mortality due to bird predation; in doing so they use a variety of devices
to protect their produce. The devices used may provoke mortalities in the bird populations due to
accidental entrapment. Presently, mortality levels due to direct killing by farmers or by entrapment
seem to be very low in the Mediterranean but they still remain undocumented. On the other hand, the
birds can affect the farm negatively It is documented that the birds can transmit diseases to farmed
fish. In Europe, birds were responsible for transmission of a number of viruses such as SVC, VHS and
IPN (Price and Nickum, 1995).
Disturbance by aquaculture activities has been proposed as another source of impact on birds. This
does not appear to have been substantiated, even though some species may be initially scared away by
farm activities (Pillay, 2004); it has been noted that marine birds eventually become accustomed to
the activities and continue feeding on the cultivated species. However, a source of impact may be a
diet change of birds. For example, sea gulls learn to directly feed on the food pellets before they reach
the water surface after being launched into the cage by the farmer (pers. obs.) or by feeding on
cultivated species, which have a physiological composition that differs from that of non-cultivated
fish; for example, their fatty acid composition (Saglik et al. 2003).
Effects of aquaculture on marine mammals seem to be quite similar to those fro marine birds;
however, the available data is even scarcer. Otters (Lutra lutra) seem to be the most harmful
mammals at salmon and trout farms. Rueggeberg and Booth (1989) reported that seals (Phoca
vitulina, Halichoerus grypus) and mink (Mustela vison) were the principal causes of predation
damage in Canada. In the Mediterranean, between 1992 and 2000, there were 40 attacks of monk
seals (Monachus monachus) on sea-bass and sea-bream farms in Turkey (Güçlüsoy and Savas 2003).
As a consequence, these mammals are killed by fish farmers; this seems to be the most severe impact
on marine mammals in the Mediterranean. In Scotland, it is possible to get a licence to shot seals to
conserve fish stocks. Additionally, deployment of fish farms provokes an increment of boat traffic
which may cause disruption to marine mammals.
In the Mediterranean, dolphins seem to be affected by sea cage aquaculture. It is known that dolphins
make excursions to fish farm facilities to feed on the associated wild fish; Díaz-López et al. (2005)
reported a change in movements of bottlenose dolphins (Tursiops truncatus) as a result of the
presence of high fish densities around floating farm cages. Furthermore, death of one dolphin per
month due to accidental entrapping in nets at the fish farms during the 15 month study was recorded
(Díaz-López, 2007). Dolphins are at the top of the food chain; therefore, they are also susceptible to
accumulation of any pollutant that is present in the food items they consume. One source of impact
may be the chemicals, such as antibiotics or antioxidants, that may be present in the food pellets, and
which may have accumulative properties (DeBryun et al. 2006). If dolphins feed on farm-aggregated
fish, such pollutants may accumulate in their body with, as yet, unknown consequences.
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