FISHING AND THE ENVIRONMENT
The effects of Fishing Methods on the Seabed
Modern fishing methods can have a severe impact on benthic communities, particularly the epifauna (animals living on the seabed) and long-lived infaunal species (animals living in the mud/sand of the sea bed), maerl and seagrasses. However, no research on the impact of fishing methods within the Moray Firth has been carried out except incidental work by the SERAD Marine Laboratory studying the effectiveness of particular trawling techniques.
Incidental capture of non-target species - Birds
The impact of mortality on Moray Firth seabird populations from accidental capture by inshore and offshore nets has not been assessed. Species at greatest risk are predators which (a) pursue their prey underwater, and (b) aggregate in dense foraging groups. These include the Red-throated Diver, Gannet, Razorbill, Shag, Great Northern Diver, Slavonian Grebe, Scaup, Common Scoter, Long Tailed Duck and Guillemot.
Incidental capture of marine mammals
Incidental capture of marine mammals in fishing gear may have contributed to the decline in numbers of some species in the North Sea. In this context, monofilament gill nets are of particular concern but these are banned in Scotland. Static gill nets are thought to present a greater hazard than demersal trawls and purse seines. The extent of incidental capture of sea mammals in fishing nets within the Moray Firth is unknown although anecdotal evidence suggests that the harbour porpoise is the most vulnerable species.
Competition between top predators and commercial fisheries
Most of the exploited fish stocks in the Moray Firth are also used as a food supply by marine mammals and birds. The extent of this interaction between man and piscivorous animals over fish stocks is notoriously difficult to study, requiring information such as the distribution and movements of fish, feeding effort, fishing effort in time and space and responses of the fishery and predators to changes in fish abundance. Work has been commissioned by SERAD within the Moray Firth to investigate the competition between seals and the salmon fishery.
Developing technology, larger boats and more efficient methods of fishing have substantially increased the fishing pressure on the stocks of many species within the North Sea and the Moray Firth. Stocks of commercially important species have been over exploited leading, at least in the case of the herring fishery to a total, if temporary collapse in the early seventies. The exploitation of new fish species in response to dwindling fish stocks may simply transfer the problem elsewhere.
There is poor understanding of the population and community dynamics of the range of fish species in the Moray Firth, their predators and the effects of environmental fluctuations upon them. Although occurring for many decades, it is difficult to see how harvesting certain species selectively will maintain the stability and integrity of the marine ecosystem. There is a need to investigate a multi-species approach to those fisheries within and related to the Moray Firth based on the ecosystem and species interaction.
Pollution is expected to have little effect upon open sea fisheries in general and there is little evidence of contamination of food fish. However, piscivorous birds and marine mammals may accumulate high concentrations of contaminants such as PCB's which raises concern for animals' reproductive abilities.
There does not appear to be any information on the effects of industrial wastes and oil spills on the fish stocks of the Moray Firth.
The effect of sewage in the Beauly and Inverness Firths was found to be small with respect of fish stocks in that area. However transfer of contaminants from fish to predators feeding on a small section of a fish stock is possible. The precise prediction of impacts is difficult because of an ignorance of the effects on fish biology of sewage effluent and the composition and long-term toxicity of future effluent.
Natural Fish Stock Changes
Changes in fish stocks may not always be induced by the fishing industry but may also be a result of environmental change. For example, pelagic fish stocks in the North Sea and adjacent waters have shown significant re-distributions which are difficult to explain just by the effect of fishing pressure. Changes may occur over long periods and over large areas. Changes in the Gulf Stream/North Atlantic Drift system and subsequent effects on more peripheral systems may be important.