The effects of trawling, dredging and ocean dumping on the eastern Canadian continental shelf seabed

Abstract

This paper presents an overview of current knowledge on the effects of trawling, dredging and ocean dumping on the eastern Canadian continental shelf seabed. The impact of trawling and dredging for fish and shellfish on marine habitats has recently attracted international attention among fisheries and environmental scientists. In Atlantic Canada, trawling and dredging are the principal methods of harvesting groundfish and scallops and ocean clams, respectively. It is estimated that fish trawlers and scallop dredges have swept tracks, cris-crossing the Canadian continental shelf, approximately 4.3 million km in length in 1985. In the past few years several studies were carried out by scientists from Canada, the United States and Europe to assess the impacts of trawling and dredging but results were inconclusive. Some studies showed physical damage as well as biological effects, whereas others indicated that the adverse effects were not considered to be serious. Fishermen are not the only potential users of the resources of the continental shelf. There is an increasing demand for good-quality sand and gravel aggregate and the ocean seabed is being seen as a possible source. The eastern Canadian continental shelf also exhibits hydrocarbon potential and operational and accidental discharges are an environmental concern. Increased marine transportation and expansion of the fishing fleet have resulted in a greater need for harbour dredging. Dredging and dredge spoil disposal were controlled by the Ocean Dumping Control Act and now the Canadian Environmental Protection Act which places restrictions on the composition of material that can be disposed of in the sea. Nevertheless some harbours contain contaminant concentrations exceeding the maximum allowable limits. It is concluded that the impacts of human activities on the continental shelf seabed environment are inevitable and the long-term effects, while difficult to determine, must be assessed. The sub-lethal effects of increased suspended sediment loads on benthic organisms and potential changes to benthic community structure are major concerns and should be the focus of further research.