333
Evaluation of Ecological Effects of the North Sea
interviewees indicated that excessive regulations meant that most fishermen considered
themselves to be operating outside the legal framework for much of the time that they
were at sea. Overall, there was little appreciation of the potential effects of the
industrial fisheries other than it was a Danish issue. Rather the main perception was
that quality was now of paramount importance, and that crews and POs (Producer
Organisations) alike were having to improve fishing and handling practices to
maintain fish quality throughout the market chain.
The Biological Effect of the North Sea Fisheries
MODELLING THE EFFECTS OF CHANGES IN THE ECOSYSTEM AND
FISHERIES:
As a result of using the 1981 stomach data for the earlier period (1977-86) and the
revised 1991 stomach data for the period 1987-1994, the biomass consumed by the
individual predators from this analysis (see Table 4) are larger by as much as 30% in
comparison with the published results from the ICES MSA Working Group. However,
these differences are small in comparison to the potential losses through illegal
landings and discards to the overall tonnage extracted from the North Sea.
Using the estimates of bycatch plus illegal landings of human consumption
species derived from the interviews above, a new MSVPA was run for the period 19871994 with a 30% increase in the catches of cod, haddock, whiting and saithe. The data
were then used to run an ECOPATH model to examine the transfer efficiencies and the
trophic impacts. A second MSVPA run was then undertaken using this revised set of
population figures and with the industrial fishery on Norway pout, herring and sandeel
reduced nominally by 50%. A third run was also undertaken to examine the effects of
using the earlier period as a starting condition for reduction of the industrial fishery.
The results were averaged over a five year projection and put into an ECOPATH
model. The transfer efficiencies and impacts of these 3 models are given in Table 7 and
Figs. 15, 16 and 17.
As can be seen in Table 7, the inclusion of 50% more in the landings of
human consumption species in the MSVPA generates a noticeable increase of 2 - 4%
in the trophic transfer efficiencies from levels IV - VIII. This shows that the roundfish
fishery, operating as it does on older age classes, can have a profound effect on the
actual efficiency of the whole system. What is more, the trophic transfer efficiencies lie
between the results of the two decadel averages, suggesting that biomass landed either
illegally or lost through discards is higher than 30%.
Looking at the effects of a reduction in the industrial fishery, only the level III
transfer efficiencies change: the 1.8% reduction is probably indicative of the fact that
any benefits coming from an increase in biomass of industrial species are dissipated
within the trophic level itself. However, it is the comparison of the baseline runs that
gives some indication of the problem. It would appear from the transfer efficiencies
that under the current ecological regime there is a strong possibility that gains in the
lower trophic levels will not lead to changes in the transfer efficiencies in the upper
Evaluation of Ecological Effects of the North Sea
interviewees indicated that excessive regulations meant that most fishermen considered
themselves to be operating outside the legal framework for much of the time that they
were at sea. Overall, there was little appreciation of the potential effects of the
industrial fisheries other than it was a Danish issue. Rather the main perception was
that quality was now of paramount importance, and that crews and POs (Producer
Organisations) alike were having to improve fishing and handling practices to
maintain fish quality throughout the market chain.
The Biological Effect of the North Sea Fisheries
MODELLING THE EFFECTS OF CHANGES IN THE ECOSYSTEM AND
FISHERIES:
As a result of using the 1981 stomach data for the earlier period (1977-86) and the
revised 1991 stomach data for the period 1987-1994, the biomass consumed by the
individual predators from this analysis (see Table 4) are larger by as much as 30% in
comparison with the published results from the ICES MSA Working Group. However,
these differences are small in comparison to the potential losses through illegal
landings and discards to the overall tonnage extracted from the North Sea.
Using the estimates of bycatch plus illegal landings of human consumption
species derived from the interviews above, a new MSVPA was run for the period 19871994 with a 30% increase in the catches of cod, haddock, whiting and saithe. The data
were then used to run an ECOPATH model to examine the transfer efficiencies and the
trophic impacts. A second MSVPA run was then undertaken using this revised set of
population figures and with the industrial fishery on Norway pout, herring and sandeel
reduced nominally by 50%. A third run was also undertaken to examine the effects of
using the earlier period as a starting condition for reduction of the industrial fishery.
The results were averaged over a five year projection and put into an ECOPATH
model. The transfer efficiencies and impacts of these 3 models are given in Table 7 and
Figs. 15, 16 and 17.
As can be seen in Table 7, the inclusion of 50% more in the landings of
human consumption species in the MSVPA generates a noticeable increase of 2 - 4%
in the trophic transfer efficiencies from levels IV - VIII. This shows that the roundfish
fishery, operating as it does on older age classes, can have a profound effect on the
actual efficiency of the whole system. What is more, the trophic transfer efficiencies lie
between the results of the two decadel averages, suggesting that biomass landed either
illegally or lost through discards is higher than 30%.
Looking at the effects of a reduction in the industrial fishery, only the level III
transfer efficiencies change: the 1.8% reduction is probably indicative of the fact that
any benefits coming from an increase in biomass of industrial species are dissipated
within the trophic level itself. However, it is the comparison of the baseline runs that
gives some indication of the problem. It would appear from the transfer efficiencies
that under the current ecological regime there is a strong possibility that gains in the
lower trophic levels will not lead to changes in the transfer efficiencies in the upper