J. Robertson et al.
298
Clearly, we do not enjoy prolific fish stocks in European waters, yet fishing effort is not
significantly decreasing. As a result the stability of fish stocks in the North Sea for
human consumption is now a matter of concern both within the fishing sector itself as
well as amongst European Union (EU) member states.
A number of factors have influenced the changes in observed fishing patterns
in the North Sea, not least of which have been the Common Fisheries Policy (CFP)
with its associated technical instruments, the continued extraction of fish resources for
oil and meal and the increased globilisation of fish products and processing (see Fig. 1
for North Sea industrial, demersal and pelagic landings from 1970 to 1994). What has
become more apparent, however, is that the integrity of the ecosystem itself may also
be at risk not only because of overfishing but also through pollution, environmental
changes and ecological forcing via the effects of a) the industrial fisheries b) current
fishing practises in the North Sea and c) other extractive processes. For example, cod,
haddock, whiting, saithe, mackerel, herring, and flatfish are generally caught for
human consumption using large mesh trawls. A large mesh ostensibly allows juveniles
to escape, but recent studies have indicated that there is a significant amount of
discarding of juveniles at sea.
In 1994, total landings from the North Sea industrial fishery in ICES Area IV
were 1307k mt, slightly below the 1974-93 mean of 1439k mt; the targeted by-catch of
human consumption species i.e., haddock, whiting, cod and saithe, was 24k mt. This is
now known to be an underestimate for the Norway pout fishery. Given that much of
this by-catch (principally and particularly from the pout fishery) comes from recruiting
age classes, any ecological overlap between the industrial and human consumption
fisheries will be likely to have an effect on the productivity of human consumption
species. However, a recent European Union study (Commission of the European
Communities, 1992) concluded that whilst a 40% reduction in the industrial fisheries
gave modest increases in whiting and haddock, there was only a minimal change to the
catches of cod, Norway pout, sandeel, saithe, herring and sprat because of increased
discarding.
Much work has been undertaken by ICES member countries on the dynamics
of all the key commercial species. Annual assessments provide managers with an
analysis of the level of exploitation with respect to two key biological stock reference
points i.e., growth and reproductive potential. Where there are sufficient data, the
Advisory Committee on Fisheries Management (ACFM) has defined a minimum
biologically acceptable spawning stock level (MBAL). Generally this equates to the
level of stock below which there is evidence of recruitment failure, or the lowest level
of spawning recorded. ACFM has identified three categories of stocks; those below
MBAL or expected to become so (i.e. outside safe biological limits), those above
MBAL and those whose state is indeterminate.
Environmental and ecosystem effects as well as fishing can distort the value of
MBAL. The ICES Multispecies Assessment Working Group has responded to this by
developing a multispecies virtual population analysis (MSVPA), involving predatorprey interactions and preferences. To add information and validate the model, a
number of stomach content surveys and feeding studies have been undertaken. But the
298
Clearly, we do not enjoy prolific fish stocks in European waters, yet fishing effort is not
significantly decreasing. As a result the stability of fish stocks in the North Sea for
human consumption is now a matter of concern both within the fishing sector itself as
well as amongst European Union (EU) member states.
A number of factors have influenced the changes in observed fishing patterns
in the North Sea, not least of which have been the Common Fisheries Policy (CFP)
with its associated technical instruments, the continued extraction of fish resources for
oil and meal and the increased globilisation of fish products and processing (see Fig. 1
for North Sea industrial, demersal and pelagic landings from 1970 to 1994). What has
become more apparent, however, is that the integrity of the ecosystem itself may also
be at risk not only because of overfishing but also through pollution, environmental
changes and ecological forcing via the effects of a) the industrial fisheries b) current
fishing practises in the North Sea and c) other extractive processes. For example, cod,
haddock, whiting, saithe, mackerel, herring, and flatfish are generally caught for
human consumption using large mesh trawls. A large mesh ostensibly allows juveniles
to escape, but recent studies have indicated that there is a significant amount of
discarding of juveniles at sea.
In 1994, total landings from the North Sea industrial fishery in ICES Area IV
were 1307k mt, slightly below the 1974-93 mean of 1439k mt; the targeted by-catch of
human consumption species i.e., haddock, whiting, cod and saithe, was 24k mt. This is
now known to be an underestimate for the Norway pout fishery. Given that much of
this by-catch (principally and particularly from the pout fishery) comes from recruiting
age classes, any ecological overlap between the industrial and human consumption
fisheries will be likely to have an effect on the productivity of human consumption
species. However, a recent European Union study (Commission of the European
Communities, 1992) concluded that whilst a 40% reduction in the industrial fisheries
gave modest increases in whiting and haddock, there was only a minimal change to the
catches of cod, Norway pout, sandeel, saithe, herring and sprat because of increased
discarding.
Much work has been undertaken by ICES member countries on the dynamics
of all the key commercial species. Annual assessments provide managers with an
analysis of the level of exploitation with respect to two key biological stock reference
points i.e., growth and reproductive potential. Where there are sufficient data, the
Advisory Committee on Fisheries Management (ACFM) has defined a minimum
biologically acceptable spawning stock level (MBAL). Generally this equates to the
level of stock below which there is evidence of recruitment failure, or the lowest level
of spawning recorded. ACFM has identified three categories of stocks; those below
MBAL or expected to become so (i.e. outside safe biological limits), those above
MBAL and those whose state is indeterminate.
Environmental and ecosystem effects as well as fishing can distort the value of
MBAL. The ICES Multispecies Assessment Working Group has responded to this by
developing a multispecies virtual population analysis (MSVPA), involving predatorprey interactions and preferences. To add information and validate the model, a
number of stomach content surveys and feeding studies have been undertaken. But the