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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

Mapleleaf mussel (Great Lakes-Western St. Lawrence population)

Status: Endangered

Last examined by COSEWIC: April 2006

Biology

The Mapleleaf mussel is a medium to large freshwater mussel that can be recognized by two bands of nodules extending in a V-shape from the beak to the edge of the shell (see cover page). The shell is thick and ranges in colour from yellowish green through light brown to dark brown. Canadian specimens reach 125 mm in length, 100 mm in height and 50 mm in width.

Females brood the young from egg to larval stage in their gills. Mature larvae 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 development into juveniles.  After a period of about 50-60 days. the juveniles drop off the fish host and grow to adulthood. In Canada, the only known fish host is the channel catfish.

The Mapleleaf mussel feeds on algae and bacteria filtered from the water column and sediment. It is a long-lived species with individuals from Manitoba living up to 64 years of age. The average life span is 22 years.

Where is this mussel found?

It is most typically found in medium to large rivers in firmly packed coarse gravel and sand to firmly packed clay/mud sediment.

This population of Mapleleaf mussel is found only in Ontario and restricted to a few rivers draining into Lake Erie and Lake St. Clair. The rivers include Ausable, North Sydenham, East Sydenham, Thames and Grand.

How many mussels are there?

The population size in East Sydenham is estimated to be 261,600 animals and for the North Sydenham it is estimated to be 25,600 animals. It is likely that the Grand and Thames River populations are an order of magnitude larger and the Ausable River population an order of magnitude smaller than the population in the Sydenham River. This would result in an overall estimate of approximately 5.5 million individuals.

Threats to the population

This population is threatened by habitat loss, degradation and effects of exotic species, particularly the zebra and quagga mussels. It occurs in areas of high human population that are affected by industrial and municipal pollution and agricultural runoff.

COSEWIC Reason for Designation:

This heavy shelled mussel that is shaped like a maple leaf, has a very small area of occupancy in watersheds dominated by agriculture with past and continuing declines due to habitat loss and degradation. Although the mussel has been lost from the Great Lakes and connecting channels due to zebra mussels, the numbers of mature individuals appear to be very large in two of the watersheds and three of five watersheds have recovery teams in place for aquatic species at risk. Zebra mussels continue to be a potential threat in watersheds that have numerous impoundments.

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

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

Mapleleaf mussel(Saskatchewan-Nelson population)

Status: Threatened

Last examined by COSEWIC: April 2006

Biology

The Mapleleaf mussel is a medium to large freshwater mussel that can be recognized by two bands of nodules extending in a V-shape from the beak to the edge of the shell (see cover page). The shell is thick and ranges in colour from yellowish green through light brown to dark brown. Canadian specimens reach 125 mm in length, 100 mm in height and 50 mm in width.

Females brood the young from egg to larval stage in their gills. Mature larvae 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 development into juveniles.  After 50-60 days, the juveniles drop off the fish host and grow to adulthood. In Canada, the only known fish host is the channel catfish.

The Mapleleaf mussel feeds on algae and bacteria filtered from the water column and sediment. It is a long-lived species with individuals from Manitoba living up to 64 years of age. The average life span is 22 years.

Where is this mussel found?

It is most typically found in medium to large rivers in firmly packed coarse gravel and sand to firmly packed clay/mud sediment.

This population is found only in Manitoba in the Roseau, Red, Bloodvein and the lower reaches of Assiniboine rivers.

How many mussels are there?

The population in the Assiniboine River is estimated to be between one and four million animals. It is not known if there are viable populations in the Red and Roseau rivers due to the current lack of extensive search effort. Only one specimen has been collected from the Bloodvein River.

Threats to the population

This population is threatened by habitat loss and degradation. It occurs in areas of high human population that are affected by industrial and municipal pollution and agricultural runoff.

COSEWIC Reason for Designation:

Small area of occupancy; all localities but one are in one system, the Red Assiniboine drainage, and a major event could extirpate the population; no evidence for recruitment (few small individuals); numerous threats including degrading water quality from agriculture, domestic waste, commercial and industrial activities.

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

A recovery strategy must be developed within one year of it being added to the SARA List