Mussel farm at Loch Torridon ©
David Donnan/SNH
The seas north and west of Scotland are considerably more diverse
than others around the UK. There are complex nearshore waters,
ranging from the very sheltered in the sealochs of western Scotland
to the highly exposed of the Atlantic sides of the Western and
Northern Isles. Further offshore there is a relatively wide shelf
area west of Orkney, but much narrower to the west of the Hebrides.
In this latter area, the shelf edge bounds the eastern side of the
Rockall Tough; to the west of the Rockall plateau is a detached
piece of shelf, that gives way to progressively deeper areas
westwards. North of the Hebrides, the Wyville Thomson Ridge
separates the Rockall Trough from the narrower Shetland-Faroes
channel.
Salmon farm at Lock Tilort ©
David Donnan/SNH
Hydrographically, the surface waters of these sea s are dominated
by the North Atlantic drift, that washes the warm waters derived
from the Gulf Stream north-eastwards into northern latitudes. The
relative warmth of Shetland compared with southern Greenland (at
the same latitude in the western Atlantic) is attributable to this
warmer current. However, waters at depths greater than about 500m
to north of the Wyville Thomson Ridge are very different from those
at the surface. Temperatures at these depths are below
0°
C as this channel comprises the main outflow of cold
Arctic Ocean waters into the wider Atlantic. Tides and a northwards
flowing coastal current dominate in nearshore waters in this area.
Fisheries
Fisheries in this area are as varied as the oceanography.
Nearshore waters of the region support the bulk of UK's aquaculture
industry, consisting predominantly of salmon and shellfish (mainly
mussels) farms. Nearshore rocky areas support a widespread
crustacean (lobster and crab) potting fishery.
The majority of vessels in the demersal fishery are locally
based Scottish
trawlers, but Ireland, Northern Ireland,
England, France, Spain and Germany also participate in these
fisheries. The main trawl fisheries target roundfish (e.g. cod,
haddock and whiting), anglerfish and the Norwegian prawn
Nephrops norvegicus (also known as scampi or the Dublin
Bay prawn). The roundfish fisheries produces a bycatch of saithe,
megrim and lemon sole. There is also a small group of Scottish
seiners targeting haddock. However many of these vessels are now
converting to light trawlers, moving to deeper waters and targeting
anglerfish with a bycatch of megrim, ling and tusk (
Brosme
brosme). Further offshore, anglerfish, megrim and hake are
also the subject of targeted fisheries.
Orange roughy (Hoplostethus
atlanticus)
At Rockall, there is a targeted fishery for haddock by Scottish and
Irish trawlers. More recently, vessels from the Russian Federation
have also fished for haddock, grey gurnards and other demersal
species since part of the bank was designated as international
waters. Along the shelf edge there is a fishery for saithe
conducted by French trawlers. In recent years, however, some of
these vessels have diverted their activity towards deep-water
fisheries including species such as orange roughy (
Hoplostethus
atlanticus), tusk (
Brosme brosme), roundnose grenider
(
Coryphaenoides rupestris) and black scabbardfish
(
Aphanopus carbo).
Other
deep water fisheries occur in the Faroe-Shetland
channel. These tend to target Greenland Halibut (
Reinhardtius
hippoglossoides), taking a bycatch of blue ling (
Molva
dipterygia), roughhead grenadier (
Macrourus berglax),
tusk (
Brosme brosme), deepwater redfish (
Sebastes
mentella) goldern redfish (
S.marinus) and Arctic
skate (
Raja hyperborea).
Spanish
gill-netters and
longliners,
many of them operating under the UK flag, work along the shelf edge
targeting anglerfish, hake and ling but occasionally moving into
deeper water to fish or deep water sharks.
There is a pelagic fishery for herring undertaken by UK,
Dutch, German and Irish vessels and a trawl fishery for mackerel,
horse mackerel and blue whiting. The industrial fishery for
sandeels is considerably smaller than that of the North Sea and
depends on availability of the resources and processing facilities
in Shetland, Denmark and the Faroes. Danish vessels also target
Norway pout.
Status of the stocks
Information on the status of the stocks has been derived from
the International Council for the Exploration of the Seas (ICES)
who have a commitment to undertake annual stock assessments in
European waters.
The cod, hake and whiting stocks to the west of Scotland are
outside safe biological limits. Recovery plans have been put in
place for cod and northern hake to ensure rapid rebuilding of the
stock spawning biomass. The spawning stock sizes of cod in 2001 and
2002 were the lowest ever recorded. Current exploitation rates will
not allow an increase in the spawning stock and a zero catch rate
been called for in the cod recovery plan. In February 2004, the
European Union introduced new regulations aimed at increasing the
quantity of mature cod to 22,000t in the sea to the west of
Scotland over the next five to ten years. Haddock stocks to the
west of Scotland are considered to be within safe biological limits
despite poor recruitment in recent years.
Anglerfish (also known as monkfish Lophius
piscatorius and L.budegassa) are currently harvested
outside safe biological limits. The fish are exploited at an early
age, prior to first maturity, due to their size and shape. Fishing
effort on anglerfish has increased rapidly in recent years as more
restrictive quotas are introduced for other species. Fishing
mortality for megrim is poorly defined, although considerable
discarding is thought to occur in some fisheries. The male megrim
attains a much smaller size than females.
Consequently the landed catch is comprised predominantly of
females. The mackerel stock is currently harvested outside safe
biological limits. For more than a decade, the horse mackerel
fishery has relied on the 1982 year class. Recruitment to this
stock has been very weak ever since and, as this year class is
fished out of the spawning stock biomass, it is unlikely that the
species will be able to sustain current levels of fishing
mortality. Current exploitation levels of Nephrops are
considered to be sustainable.
Changes in the legal status of waters to the west of Rockall,
especially over the Hatton Bank, have meant that fisheries,
particularly for haddock, in this area have become much less
closely regulated than in former years. The haddock stock has
consequently fallen dramatically and there are calls for catches to
be reduced to the lowest possible levels. There are also concerns
for the megrim and whiting stocks. All exploited deep-water stocks
are in poor shape due to lack of effective fisheries management.
Newly discovered stocks of orange roughy were overexploited before
advice on management could be given. As a consequence,
recommendations have been made for no directed fisheries on this
species. A ban on a directed fishery for blue ling has also been
suggested.
The fishing mortality of herring is thought to be relatively
low. However the state of the stock is uncertain and the fishery
appears to be dependant on occasional strong year classes. There
are indications that this stock may have declined considerably in
recent years and as a consequence, fishing mortality may actually
be comparatively high. There is no data regarding the Norway pout
and sandeel populations. For sandeels, however, precautionary
management includes closure of the fishery from August each year to
avoid interaction with breeding seabirds.
Environmental problems
As well as the current poor state of many north and western
fish stocks, particular environmental problems caused by fisheries
in this are include:
- By-catch of fulmars on long-lines. There have
been only a few studies in this area, and no definitive catch rate
is known, however an annual catch of 10,000+ has been
estimated.
- Bycatch and discards in demersal fisheries are
high. For example, the Nephrops fishery discards large
amounts of juvenile haddock and whiting. Juvenile cod are also
discarded from other demersal fisheries. The loss of these juvenile
fish will be a serious impediment to future stock rebuilding.
- Damage to the Darwin Mounds, a globally unique site holding the
cold-water coral Lophelia pertusa. Although located at
1000m depth some 150km NW of the Outer Hebrides, trawl nets have
been towed through the site destroying these cold water coral
mounds. In 2003, the Darwin Mounds were given emergency protection
through the CFP which banned demersal fishing. This protection was
made permanent in August 2004.
- Seamount habitats and deep sea fisheries. Seamounts are
underwater mountains rising over 1000m. Due to strong localised
currents and upwellings, they are hotspots of marine biodiversity
often with large numbers sharks, marine mammals and seabirds. They
are also important areas for deep sea fisheries. Concern regarding
overexploitation of long-lived, slow growing, late maturing species
such as the orange roughy is increasing. The Hebridean Terrace
Seamount is thought to be inhabited by the main component of the
spawning stock for orange roughy. In addition, trawling impacts on
the benthic communities which includes deep water coral species.
OSPAR have placed seamounts on their list of threatened habitats
that require conservation. No moves, however, are currently being
made by the European Union to protect seamounts.