Impacts of acid mine drainage on juvenile salmonids in an estuary near Britannia Beach in Howe Sound, British Columbia

The abandoned copper mine at Britannia Beach, British Columbia, has been releasing acid mine drainage (AMD) into Howe Sound for many years. To assess the impacts of AMD on juvenile salmonids in the Britannia Creek estuary, we compared fish abundance, distribution, and survival at contaminated sites near the creek with uncontaminated areas in Howe Sound. Water quality near Britannia Creek was poor, particularly in spring when dissolved Cu exceeded 1.0 mg.L-1 and pH was less than 6. Beach seine surveys conducted during April-August 1997 and March-May 1998 showed that chum salmon (Oncorhynchus keta) fry abundance was significantly lower near Britannia Creek mouth (0-1.2.100 m(-2)) than in reference areas (11.5-31.4.100 m(-2)). Laboratory bioassays confirmed that AMD from Britannia Mine was toxic to juvenile chinook (Oncorhynchus tshawytscha) and chum salmon (96-h LC50 = 0.7-29.7% in freshwater and 12.6-62.2% in 10 ppt water). Chinook salmon smolts transplanted to surface cages near Britannia Creek experienced 100% mortality within 2 days. These results demonstrated that juvenile salmonids are vulnerable to AMD from Britannia Creek: their abundance peaks during spring when Cu concentrations are highest and toxicity is greatest in surface freshwater, which matches their preferred vertical distribution.