Environmental Protection Branch, Environment Canada, Pacific and Yukon Region, 1998. The Dungeness crab is a good environmental indicator of toxic contaminants because it bioaccumulates contaminants in its tissue especially from the consumption of food containing the contaminants. The Dungeness crab is also a useful indicator species due to its importance to commercial, recreational and First Nations harvests. There are differences in levels of dioxins and furans for crab and sediment between mill outfall sites.
Outfalls located on the open coast show a less dramatic decrease in contaminants.
In fact, sediments from some of these open coast sites have shown some increases in dioxin and furan levels since 1993. The other mills are located on fjord sites and show a faster contaminant recovery likely due to high clean sediment input from discharging river systems. Other processes such as bioturbation, or the biological mixing of sediments, rate of sediment burial and sediment chemistry can affect this difference in contaminant levels between crab and sediment at each location along the coast. Initial monitoring from 1987 to 1989 documented elevated dioxin and furan levels in edible fish and shellfish collected from sites near nine of these mills. The federal government responded by issuing harvesting restrictions on various crab, clam, prawn, shrimp, and oyster fisheries, requiring mills to conduct annual monitoring and introducing legislation to control dioxin and furan discharges.