Image of deep sea redfish © SNHDeep-water fisheries can be defined as those which take place
at depths greater than 400m and, in waters to the west of the UK,
are a relatively recent phenomenon. Although it is known that
vessels from the former USSR fished for roundnose grenadier in this
area as far back as the 1960s and that the Germans targeted
aggregations of blue ling in the 1970s, the main development of the
fisheries did not take place until the late 1980s when French
vessels fishing to the west of Scotland began to move into deeper
water and to develop markets for the new species they found there.
Today, they have been joined by Scottish and Irish vessels which
exploit the same species and sell much of their catch into the
French market. A number of Spanish longliners and gill-netters,
some of them registered under the UK flag, also target deep living
species such as hake, ling and deep-water sharks.
The waters to the west of the UK are divided by a massive
underwater feature, the Wyville-Thomson Ridge, which runs between
Shetland and the Faroes dividing the cold Arctic waters to the
north from the relatively warm Atlantic waters to the south. North
of this ridge, water temperatures at 600m can be below 0°C and
relatively few species are able to survive. Some Scottish vessels
work here fishing for Greenland halibut at the boundary between the
cold Arctic water and the relatively warm water which overlies it.
South of the ridge, in the area known as the Rockall Trough, water
temperatures are considerably higher and consequently there is a
much greater diversity of life and it is here that the major
fisheries take place. Species caught on the Rockall Trough include
roundnose grenadier, blue ling, black scabbardfish, orange roughy,
greater forkbeard, Portuguese dogfish and leafscale gulper
shark.
Orange roughy (Hoplostethus
atlanticus)Since the early days of deep-water fisheries, scientists have
warned that they are likely to be extremely vulnerable to
over-fishing; this is because of a number of unusual features of
the deep-water environment and the biology of the fish that live
there. The deep sea is a cold, dark place. No plants can grow there
and everything that lives there depends for its food source on
small particles of dead plants and animals which rain down from the
surface many metres above. As a consequence, there is little food
available and so the fish that live there have adapted by growing
very slowly, living for a very long time and producing only
relatively small numbers of offspring. This means that any fish
removed by fisheries may take years or decades to be replaced by
the natural growth of the population.
In 1989 French vessels fishing west of the UK discovered a
major aggregation of orange roughy on the Hebrides Terrace
Seamount. The fishery developed rapidly and catches peaked at 3600
tonnes in 1991. By 1994 the annual catch had fallen to less than
180 tonnes and it is now believed that in the short time this
fishery operated, the stock was effectively fished out. It is now
known from fisheries elsewhere in the world that this species is
capable of sustaining only extremely low rates of exploitation and
that recovery from severe depletion is likely to take decades or
longer.
Until recently there was no management of these fisheries.
However in 2002, the EU imposed a management system based on total
allowable catch (TACs) and quotas. Because quota allocation was
based on a long term history of catches, the UK and Ireland
received only very small quotas. The majority of the quota went to
the French, however even they have had to reduce their catches
considerably. Current scientific advice from ICES is that fishing
mortality is still higher than the stocks can sustain and further
reductions will be necessary if we are to manage the stocks for the
long term.