334
J. Robertson et al.
levels in line with those observed in the 1977-86 period, but that inclusion of illegal
landings etc., brings the estimates together.
The impact diagrams (Figs, 15, 16 and 17) show that the effects of those
changes on pairwise interactions are small but that cumulatively the negative impacts
of fisheries in the earlier decade were spread across all the trophic levels and have now
become more concentrated.
Discussion with Conclusions and Recommendations
(a) Fisheries are experiencing reduced levels of cod, haddock, whiting, mackerel
and herring. This means that fish imports are required for human consumption
within the European Community to offset the shortfall of fishery products from
our own seas.
(b) The food preferences and requirements of the fish within the North Sea have
noticeably altered during the period 1987 to 1994.
(c) Human consumption species eat mostly sandeel and Norway pout in the fish
component of their diet.
(d) Breeding failures in bird colonies are evident as a consequence of reduced
quantities of fish high in lipids to feed the young (see for example Anon, 1994).
Probabilities of mammals encountering suitable prey food are diminishing.
As expected, the introduction of the illegal landings and discards into the biomass
models has a significant effect on the upper trophic levels in terms of their transfer
efficiencies; the reduction of the industrial fishery only effects level III. The impact
diagrams show only small changes in the interactions and impacts between the
predator and prey species given the 1994 situation, compared to the effects that
removal of the industrial fishery would have had in the earlier period.
It would appear that the high levels of illegal landings and discards from the
human consumption fishery mitigate against the full effect of a reduction in the
J. Robertson et al.
levels in line with those observed in the 1977-86 period, but that inclusion of illegal
landings etc., brings the estimates together.
The impact diagrams (Figs, 15, 16 and 17) show that the effects of those
changes on pairwise interactions are small but that cumulatively the negative impacts
of fisheries in the earlier decade were spread across all the trophic levels and have now
become more concentrated.
Discussion with Conclusions and Recommendations
(a) Fisheries are experiencing reduced levels of cod, haddock, whiting, mackerel
and herring. This means that fish imports are required for human consumption
within the European Community to offset the shortfall of fishery products from
our own seas.
(b) The food preferences and requirements of the fish within the North Sea have
noticeably altered during the period 1987 to 1994.
(c) Human consumption species eat mostly sandeel and Norway pout in the fish
component of their diet.
(d) Breeding failures in bird colonies are evident as a consequence of reduced
quantities of fish high in lipids to feed the young (see for example Anon, 1994).
Probabilities of mammals encountering suitable prey food are diminishing.
As expected, the introduction of the illegal landings and discards into the biomass
models has a significant effect on the upper trophic levels in terms of their transfer
efficiencies; the reduction of the industrial fishery only effects level III. The impact
diagrams show only small changes in the interactions and impacts between the
predator and prey species given the 1994 situation, compared to the effects that
removal of the industrial fishery would have had in the earlier period.
It would appear that the high levels of illegal landings and discards from the
human consumption fishery mitigate against the full effect of a reduction in the