The Return of Atlantic Salmon Salmo salar to Trout Lake, North Bay, Ontario

Abstract

Abstract In 1935, landlocked Atlantic salmon or ouananiche Salmo salar were introduced into Trout Lake, a 1,674-ha oligotrophic lake. The salmon reproduced in Four Mile Creek and became the only naturally reproducing population in Ontario. Anglers reported good catches of salmon in the 1950s and 60s, with fish up to 6 kg taken. In 1967, a train derailment resulted in the spillage of an unspecified volume of zinc concentrate into the Four Mile Creek watershed. Water quality monitoring completed in 1979 documented zinc levels in Four Mile Creek downstream of the derailment area ranging from 130 to 340 µg/L. In retrospect, it was believed that this elevated level of zinc resulted in adult salmon avoiding Four Mile Creek. Since this was the only stream suitable for spawning, reproduction ceased and salmon disappeared. The last known catch of Atlantic salmon in Trout Lake occurred in the early 1970s. In 1980, approximately 250,000 tonnes of zinc-contaminated soil was excavated from the area. In situ toxicity studies in 1981 produced 20% mortality of rainbow trout Oncorhynchus mykiss yearlings during a 48-hour exposure period downstream of the derailment area. In-stream zinc concentrations ranged from 110 to 160 µg/L during the exposure period. Rainbow trout stocked into Four Mile Creek from 1983-88 survived. Atlantic salmon were first reintroduced in 1989 as fall fingerlings. Adult salmon appeared in the creek in November 1992, and again in 1994 and 1995. Electrofishing studies confirmed the presence of naturally reproduced juvenile salmon in 1994 and 1995. As yet the population of adult salmon in Trout Lake is low but may increase as naturally reproduced salmon smolt and enter the lake. Zinc concentrations in Four Mile Creek have continued to decline as a function of time. In 1994, they ranged from 7 to 48 µg/L.