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

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others (mainly benthic and high value slow growing) have decreased as a result of overfishing
(Goni et al. 2000). Species like lobster (Palinurus elephas) and red coral (Corallium rubrum)
have been identified to be under pressure more than a decade ago (FAO 1997). Yet,
professional fishing is not the sole agent of overexploitation of Mediterranean species; sport
fishing, mainly with harpoons, spears and rods, has a substantial impact, especially on the
largest and less abundant species such as groupers and croakers (Goni et al. 2000). A series of
measures have been adopted by various countries to reduce the effects of these threats,
including a ban on some fishing gears, exclusion of some types of fishing from sensitive areas
(such as trawling at depths shallower than 50 m) and the creation of MPAs. However,
conserving or replenishing exploited species is not the only or main objective of all MPAs. A
number of other objectives exist, ranging from the protection of sensitive habitats of
endangered species (e.g. the Sporades National Park of the eastern Mediterranean for the
monk seal (Monachus monachus), to the protection of singular assemblages (e.g. the
coralligenous community of the Columbretes Islands Marine Reserve, western
Mediterranean), and to conserve or restore relatively pristine habitats (Goni et al. 2000).
Compatibility of mariculture with MPAs is not straightforward. The size of the farms, the
characteristics of the receiving environment, and the specific objectives of the MPAs are
critical issues. However, it is reasonable to assume that impacts from aquaculture must be
minimized to prevent any deterioration to such sites. The management of aquaculture
activities falls under a number of high level objectives defined under the Convention for the
Protection of the Mediterranean Sea against Pollution (the Barcelona Convention 1976).
As noted by Huntington et al (2006), as well as national or international legislation applicable
to SPAMI management plans, the Barcelona Convention also requires a number of specific
provisions which would be directly applicable to management of aquaculture activities:
• the strengthening of the regulation of the release or dumping of wastes and other substances
directly or indirectly to impair the integrity of the area;
• the strengthening of the regulation of the introduction or reintroduction of any species into
the area;
Where such legislation does not exist, however, the requirements of the Barcelona
Convention should ensure that management plans are suitably robust to afford a high level of
environmental protection.
Effects on biodiversity in general, including species diversity
Although some species are directly affected by aquaculture and there is a general tendency for
species diversity beneath cages to decrease, it has not yet been established with certainty that
fish farming is a threat to biodiversity. According to Margalef (1997), there is a clear
distinction between biodiversity (i.e. the total number of available species or genotypes in an
area) and ecological diversity or eco-diversity, which can be inferred by sampling local biotic
communities. In this context, local changes in community structure that affect a small patch
of the seabed or a few cubic meters of seawater, cannot be considered as a decline in
biodiversity. By contrast, threats to biodiversity arise when a specific type of habitat (usually
rare or supporting an endangered species or a key-habitat supporting life over a very large
area) are severely degraded over large spatial scales or when populations of K-selected
species (i.e. those having a large size and low reproduction rate) are reduced to unsustainable
sizes. At present, most of the scientifically documented effects of fish farming are those on
macrofaunal invertebrates (see section on organic enrichment below) within a zone beneath
and close to the farm cages. These organisms are ecologically important but it is very unlikely
that they will become extinct or that their population at the larger spatial scale will be
significantly affected. The potential problems affecting biodiversity in relation to aquaculture