Irish Sea
Brown crab catch © David
Donnan/SNH
The Irish Sea lies between Britain and Ireland and surrounds
the Isle of Man. It covers just over 100,000 km2. The North Channel
and St. George's Channel connect it with the Atlantic Ocean. A
relatively shallow sea, it is less than 90m deep in most places
with shallow sandbanks off the Irish and north-west English coasts.
The sea floor is mostly of mixed sediments, with rocky areas off
Anglesey and muddy areas to the west of the Isle of Man.
There are a few oil and gas fields in the south-eastern Irish
Sea and major shipping lanes running into Liverpool off the coast
of north Wales.
Fisheries
Herring © Chris Martin/SNH
The major fisheries are for demersal species, caught using a
variety of gears. These are mixed fisheries with many stocks
exploited together in different combinations in different
fisheries. The majority of vessels target Nephrops with
otter trawls, either a single or twin rig. This fishery occurs
predominantly in the muddy area west of the Isle of Man - one of
the common names for Nephrops is Dublin Bay prawn. Bycatch
from the Nephrops fishery includes haddock, cod and plaice
which is also landed. In addition, whiting is caught, but usually
discarded. Cod, haddock, whiting, and plaice are also targeted
directly. These trawl fisheries also have a commercially important
bycatch, consisting of anglerfish, hake and sole. In the southern
Irish Sea there is a small fishery for rays. In the eastern Irish
Sea, beam trawlers target sole, with a bycatch of plaice, rays,
brill, turbot, anglerfish and cod. Inshore, gillnets and tangle
nets are used to catch cod, bass, grey mullet, sole and plaice. The
large estuaries bounding the eastern Irish Sea support pot
fisheries for crab, lobster and whelk. There are also hydraulic
dredge fisheries for razor fish and dredge fisheries for scallops.
The main pelagic fishery in the Irish Sea is for herring, however,
the number of vessels has declined to very low levels in recent
years.
Status of 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 Irish Sea cod stock is in such a poor state, and is
outside safe biological limits. The high rate of fishing mortality
has caused a long-term decline in the spawning stock biomass. In
2000, an emergency spawning closure was introduced to maximize egg
production. The closure has been continued in recent years,
although restricted to the western Irish Sea. A recovery plan has
been proposed that should include zero catch rates. In February
2004, the European Union introduced regulatory measures for the
recovery of cod stocks in the Irish Sea. The aim is to increase the
quantity of mature fish to more than 10,000t over the next five to
ten years. These measures included controls for the setting of
total allowable catch (TAC), fishing effort limitation (number of
days at sea and gear restrictions) and restrictions on landing
ports, stowage and transport of cod.
The whiting stock is also outside safe biological limits and a
recovery plan with zero catch rate proposed. Haddock had very
strong 1994 and 1996 year classes, consequently there was a
substantial increase in stock size. This stock is concentrated in
the western Irish Sea and suffered very high rates of fishing
mortality. The stock is currently harvested outside safe biological
limits. The plaice stocks are considered to be within safe
biological limits, with an increasing stock size and reduced
fishing mortality. In contrast, sole are considered to be outside
safe biological limits, with a need to cut fishing mortality by
10%. The Nephrops stock of the Irish Sea is considered to
be fully exploited. Concern, however, has been raised over the
increasing use of twin rigs which are known to have a greater
impact on roundfish stocks (e.g. cod, haddock and whiting). The
status of the herring stock is uncertain, although it appears to
have recovered from the collapse in the 1970s.
Environmental problems
Particular environmental problems in the Irish Sea caused by
fisheries include:
- Effective extinction of common skate, long-nosed skate and
angel shark. These large long-lived species of elasmobranch
with a low reproductive rate have all but disappeared from the
Irish Sea.
- Scallop dredgers have been demonstrated to have serious
detrimental impacts resulting in long term changes in the benthic
community and a loss of benthic biodiversity. Mobile, robust and
scavenging taxa are more abundant while slow-moving or sessile,
fragile taxa are less abundant. In addition, as the seabed is
ploughed to a single homogeneous environment, there is a loss of
habitat variability and complexity which leads to a loss of
biodiversity.
- Nephrops trawls have also been shown to have a
negative impact on the benthic community, although probably over a
shorter time frame. The number of species and the abundance of
individual species were found to decrease as a response to nephrops
trawling. Of particular concern was the loss of the burrowing
urchin Brissopsis lyrifera at some sites and impacts on
deep burrowers such as the mudshrimp Jaxea nocturna and
Callianassa subterranea. These burrowing megafaunal
species have an important role in maintaining the structure and
oxygenation of muddy sediments.
- Discarding of small, juvenile fish such as cod
and haddock in the Nephrops, roundfish and flatfish
fisheries are very high. The proportion of the total catch
discarded has been gradually increasing. For example in the
Nephrops fishery, over 60% of the whiting bycatch is
discarded. Recent EU legislation to increase mesh sizes in the
roundfish fishery to 100mm, should help alleviate this problem.
However, the Nephrops fishery still uses 70 and 80mm
meshes. Although obligatory square mesh panels were introduced in
1994, the proportion of small whiting caught and discarded has
continued to increase. Additional measures are needed which could
include increases the mesh size of the cod end and square mesh
panels, and the introduction of separator grids or fixed grids in
the trawl to enable undersized fish to escape.
The recently completed the Irish Sea Pilot was set up in 2002
to examine the potential for an ecosystem-based approach to
managing the marine environment at the regional sea level.
Specifically, the pilot looked at the integration of nature
conservation into key sectors, including fisheries, in relation to
sustainable development. Further information and the final report
are available>>>