because cages were generally small (5 m2)
and ofwood construction; and proximity to
supporting infrastructure such as roads
and distribution networks. In many cases
therefore, farms were located in sheltered
emba~ments, often at the head of fiords
and sea-lochs.
Improvements in technology,
especially cage design and construction,
for example robust 15 m2 aluminium cages
with 8 m deep nets allowed expansion into
more open sites. The early success of the
industry was built upon by developing
new sites although as the availability of
new sites declined existing sites were
expanded. Thus, inmany cases the original
production of 50 to 100 tonnes per year
was increased four or five fold with some
sites producing three to four hundred
tonnes per year.
The development of farming in coastal
waters of southern Europe and North
America has generally followed
development in northern Europe. Rather
than an initial start-up period with small
production units, the tendency has been
for the establishment 3f large production
units, but following the European example
of often being located in sheltered coastal
waters. This has created environmental
issues similar to those experienced by the
cage farmingindustry in northern Europe.
The Physical Environment of
Embayments Used for Cage CultureIn a number of European countries
the initial development of fish farming
took place in coastal embayments. While
these embayments provide suitable
locations for cage farming in terms of the
proximity of deep water to the shore and
shelter, they have a number of distinct
physical features which can compound the
ecological effects of the waste released
from cdge farms.
A common feature of many of the
embayments used for cage farming is a
restricted entrance. Such restrictions,
which are narrow or shallow or both,
restrict the exchange of water between the
embayment andmore open coastal waters.
In addition, shallow entrance sills prevent
the penetration of seawater at depth; thus,
deep water within the embayment may
become isolated for a period of time which
in some fjords can be in the order of years
(Lazier 1963; Gade and Edwards 1980).
In general, water currents are weaker
inshore and since currents are due in part
to wind, may be considerably reduced in
sheltered inshore locations. For example,
Gowen et al. (1 988) found that at a number
of fish farm sites in Scottish sea-lochs
there was little evidence of a tidal
component to water movement and that at
such sites the maximum current speed
was in the order of 0.16 mas1. Further
offshore and outside these embayments,
tidal currents might be expected to be
higher, and for the Scottish west coast, are
in the order of 1 md. In addition, it has
been shown that for some coastal regions
there is often a residual flow of water. On
the west coast of Scotland and Norway for
example, there is a northerlyflow of coastal
water. Suchflow ofwater might be expected
to aid the transport and dilution of fish
farm waste.
Many coastal embayments have rivers
which discharge into them. Within such
embayments there is generally an
estuarine circulation with a net seaward
flow of surface brackishwater and a
compensati.ng landward flow at depth.
Estuarine circulation may aid dispersal of
waste from the immediate vicinity of the
farm, but there is also the potential for
recirculati.on of ernbayment water. This is
particularly the case when tidal energy
causes mixing at entrance shallows or at
narrows. Gowen et al. (1983) estimated
that approximately 50% of the water
1eavingLochArdbhair (a small sea-loch on
the west coast of Scotland) during the ebb