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Consultation Workbook on the addition of the Atlantic salmon (Lake Ontario population), Rainbow mussel, Mapleleaf mussel (Saskatchewan-Nelson population) and Mapleleaf mussel (Great Lakes-Western St. Lawrence population) to the SARA List

Atlantic salmon (LakeOntariopopulation)

Status: Extirpated

Last examined by COSEWIC: April 2006


The Atlantic salmon has a “trout-like” body with an average length of about 457 mm.

The Atlantic salmon in Lake Ontario completes its life cycle within the Lake Ontario watershed. Adult salmon migrate to spawning streams as early as March and April. The female selects a nesting site in a gravel-bottom riffle area and then uses her caudal fin to dig a nesting depression. Eggs and sperm are deposited in the depression and then are covered with gravel by the female. The average female deposits approximately 1540 eggs/kg of body weight. Following spawning, any surviving adult fish return downstream and begin feeding. They may return the following or subsequent years to spawn again.

Young salmon remain in the streams where they hatch, for two to three years before they migrate to Lake Ontario where they remain for up to two years.  Once mature, they migrate back to the stream where they hatched, to spawn. The Lake Ontario population was thought to ascend the streams in preparation for spawning in two separate runs, one in early spring (almost immediately following ice out) and another in September and October. East of Toronto, salmon entered streams in the fall during the spawning season in October and November with exceptionally few entering in late September while both the Humber and the Credit rivers are stated to have had both spring and fall runs.

Juvenile Atlantic salmon living in streams feed mainly on aquatic insect larvae. Upon entry to Lake Ontario, the fish feed opportunistically on aquatic insects and fish that are near the water surface. As they grow to adulthood, fish becomes an increasingly dominant component of their diet. In Lake Ontario, the primary forage fish available are two non-native species namely alewife and rainbow smelt. Adults cease feeding when they begin their migration to the spawning grounds.

Where is this fish found?

Atlantic salmon juveniles and spawning adults prefer streams with clean water and temperature that seldom rises above 25°C and naturally graded and stable beds with stony bottoms that range from coarse sand and gravel to large boulders. Little is known about the specific stream or lake habitat required by the Lake Ontario population of Atlantic salmon.

This population is restricted to Lake Ontario.

How many fish are there?

There are no remaining Atlantic salmon that are native to Lake Ontario.

Reports of the historical population levels of Atlantic salmon in Lake Ontario have been largely based on casual observations or indications rather than rigorous population studies. Marked decline in large numbers of salmon began in mid-1800s and salmon were no longer present before 1900. Today, the Lake Ontario ecosystem contains apparently suitable habitat for Atlantic salmon; however, attempts at stocking with non-native Atlantic salmon have failed to establish reproducing populations.

Threats to the population

The disappearance of Lake Ontario salmon is mostly attributable to degradation of its habitat caused by the removal of native forests for timber, clearing the land for agriculture, construction of dams for mills across rivers that prevented access to spawning grounds and commercial fishing industry that harvested large quantities of salmon.

COSEWIC Reason for Designation:

Once a prolific species throughout the Lake Ontario watershed, there has been no record of a wild Atlantic salmon since 1898. The Lake Ontario Atlantic salmon was extinguished through habitat destruction and through overexploitation by a food and commercial fishery. Attempts to re-establish Atlantic salmon through stocking have failed, and the original strain is no longer available.

What will happen if this fish is added to the SARA List?

A recovery strategy will have to be developed within two years of it being added to the SARA List.

Rainbow mussel

Status: Endangered

Last Examination by COSEWIC:  April 2006


The Rainbow mussel is a small freshwater mussel with an average length of about 55 mm. The shell is yellowish, yellowish-green, or brown (in old specimens) with numerous narrow and/or wide broken dark green rays that cover the whole surface of the shell.

The Rainbow mussel is a long-term brooder. Adults spawn in late summer and females brood the young from egg to larval stage in their gills over the winter months. In the spring, when the larvae are mature, they are released into the water and when they encounter a suitable fish host, will attach themselves onto the gills of the fish. Eventually the larvae are encased onto the gills and proceed to undergo a period of development into juveniles. Juveniles eventually drop off the fish host and grow to adulthood. In Canada, suspected fish hosts include striped shiner, smallmouth bass and largemouth bass, green sunfish, greenside darter, rainbow darter and yellow perch but no testing has been done to confirm these host(s) with certainty.

Rainbow mussels feed on algae, bacteria and other organic material filtered from the water column and sediment. Juveniles live completely buried in the sediment where they feed on similar food items obtained directly from the sediment or water column.

Where is this mussel found?

The Rainbow mussel is most abundant in small to medium-sized rivers, in or near riffles and along the edges of emergent vegetation in moderate to strong current. It occupies sediment mixtures of cobble, gravel, sand and occasionally mud or boulder and is most numerous in clean, well-oxygenated water of less than 1 metre. It can also be found in inland lakes in shallow nearshore areas of firm sand or gravel.

The Rainbow mussel is found only in southern Ontario in the Grand, Maitland, Moira, Saugeen, Sydenham, Thames and Trent Rivers and Lake St. Clair delta. The species appears to have been lost from the lower Great Lakes and connecting channels.

How many mussels are there?

A very small population, estimated at 7,200 individuals, occupies the Canadian waters of the Lake St. Clair delta, but it is declining at an estimated rate of 7% per year based on data collected from 9 sites in 2001 and 2003. Populations in the Ausable, Grand, Saugeen and Sydenham Rivers are small. The population in the East Sydenham River consists of an estimated 18,900 individuals, but appears to be declining. The upper Thames River population is estimated at 40,000 mussels, but may also be declining. The Maitland River supports the largest and healthiest population.

Threats to the population

The Rainbow mussel has been lost from the lower Great Lakes and connecting channels due in large part to impacts of the zebra mussel. If zebra mussels become established in the reservoirs of impounded rivers, they could pose a threat to riverine populations of this and other native mussels. Zebra mussels have already been found in 2 reservoirs in the Thames River. Heavy loadings of sediment, nutrients and toxic substances from urban and agricultural sources have degraded mussel habitat throughout southern Ontario. Studies have shown that the Rainbow mussel is particularly sensitive to copper and ammonia.

COSEWIC Reason for Designation:

This attractive yellowish green to brown mussel with green rays is widely distributed in southern Ontario but has been lost from Lake Erie and the Detroit and Niagara rivers and much of Lake St. Clair due to Zebra mussel infestations. It still occurs in small numbers in several watersheds but the area of occupancy and the quality and extent of habitat are declining, with concern that increasing industrial agricultural and intensive livestock activities will impact the largest population in the Maitland River.

What will happen if this mussel is added to the SARA List?

A recovery strategy must be prepared within one year of it being added to the List.