Despite positive socio-economic effects associated
with the development of aquaculture in Europe, concern
has been expressed about the impact of fish farming on
the marine environment and the prospects for its
sustainability [1–4]. The problem has two dimensions:
the first, relating to environmental damage due to
pollution and habitat degradation; the second, to the
pressure which aquaculture imposes on wild fish stocks
via the demand for processed feed [5]. The present
report is concerned with the first of these issues, and
focusses on net cage mariculture. This has been a
particular source of controversy, amid evidence that the
production methods hitherto practiced by many fish
farmers have led to a number of adverse environmental impacts. These may not only generate problems for fish
farmers themselves, via negative feedback on production
through reduced growth and survival [6], but also costs
for society as a whole. For example, mariculture
pollution may degrade the marine environment in ways
which reduce the flow of benefits to users and non-users
(e.g. lower water quality as a result of greater turbidity
may reduce the recreational or amenity value of a site).
Estimating the magnitude of these externalities, and
suggesting possible ways in which they can be mitigated
or ‘internalised’, poses a challenge for environmental
economists and others concerned with the sustainability
of aquaculture [7–13].
In this context, salmon farming has received considerable
attention, since it is believed by some to be one
of the anthropogenic sources of eutrophication in
enclosed coastal areas as well as being implicated in a
range of ecological problems such harmful algal blooms
(HABs). While the evidence for some of the more
serious environmental impacts is far from proven, it is