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Ausable Bayfield Conservation Authority

Mussel Species at Risk

Introduction

The Ausable River Recovery Team has spent considerable time documenting the species at risk in the Ausable River watershed. This has taken place since the summer of 2002. Extensive mussel surveys have been conducted resulting in the discovery of a live Snuffbox in the Ausable River, a mussel species thought to be lost from the river.

In all, the Ausable River is home to 20 species at risk, including six fishes, six mussels, and eight reptiles.


Mussel Species

The Ausable Bayfield Conservation Authority (ABCA) and its scientifically-significant work surveying populations of species-at-risk mussels in the Ausable River has reached the national stage. Fisheries and Oceans Canada has published a story on the work in this watershed: Watching Recovering Mussels in Ontario’s Ausable River

In a publication on an early 1900s survey of the Ausable River, it was stated that the lower Ausable River used to be covered in mussel shells and that prior to the Canada Company Cut (1875), the river was well suited to support mussel life. Poor water quality, habitat destruction, siltation and invasive species have been identified as reasons for mussel species decline. The following six mussels are listed as species at risk in the Ausable River.

Northern Riffleshell
(Epioblasma torulosa rangiana)
The Northern Riffleshell is a globally endangered freshwater mussel. It is small with a brown-yellow shell covered in green rays and can be found in sand/gravel riffle areas of streams or rivers. The fish host species is most likely a darter. Northern Riffleshells have suffered a dramatic reduction (95%) in their range over the last century. Recent surveys of the Ausable River indicate that the population has been reduced to a few individuals, with no signs of reproduction.
*ENDANGERED* (Last examined by COSEWIC in 2010)

Reason for Designation: This small freshwater mussel is restricted to two rivers in southern Ontario. Since the original COSEWIC assessment (2000), a small, possibly reproducing population was discovered in the Ausable River although only 16 live individuals, including one juvenile, have been found over the last 10 years. Recruitment is occurring at several sites along the Sydenham River and the population appears to be stable, but the perceived recovery could be due to increased sampling effort over the past 12 years. The main limiting factor is the availability of shallow, silt-free riffle habitat. Both riverine populations are in areas of intense agriculture and urban and industrial development, subject to siltation and pollution. Only four populations in the world, including the two in Canada, show signs of recruitment.

Status History: Designated Endangered in April 1999. Status re-examined and confirmed in May 2000 and April 2010

Wavy-Rayed Lampmussel
(Lampsilis fasciola)
The Wavy-Rayed Lampmussel is a medium-sized mussel with a thick, round, yellow-green shell with distinctive green wavy rays. This species prefers riffle areas of medium-sized streams with stable sand/gravel bottoms. Northern populations have declined significantly in recent years. Clear water with a steady flow is essential for the survival of the Wavy-Rayed Lampmussel.
*SPECIAL CONCERN* (Last examined by COSEWIC in 2010)

Reason for Designation: This medium-sized freshwater mussel is confined to four river systems and the Lake St. Clair delta in southern Ontario. Since the original COSEWIC assessment of Endangered in 1999, surveys have identified a large, previously unknown reproducing population in the Maitland River. The mussels in the Thames River are also now reproducing. The largest population is in the Grand River; smaller but apparently reproducing populations are in the Ausable River and Lake St. Clair delta. Although water and habitat quality have declined throughout most of the species' former range in Canada, there are signs of improvement in some populations but habitats in Great Lakes waters are now heavily infested with invasive mussels and are uninhabitable for native mussels. The main limiting factor is the availability of shallow, silt-free riffle/run habitat. All riverine populations are in areas of intense agriculture and urban and industrial development, subject to degradation, siltation, and pollution. Invasive mussels continue to threaten the Lake St. Clair delta population and could be a threat to populations in the Grand and Thames rivers if they invade upstream reservoirs.

Status History: Designated Endangered in April 1999. Status re-examined and confirmed in October 1999. Status re-examined and designated Special Concern in April 2010.

Snuffbox
(Epioblasma triquetra)
The Snuffbox is a small mussel with a smooth, thick, triangular shaped, yellow-green shell with broken dark green rays. This mussel is often found deeply buried in stable sand/gravel substrates in riffle areas of fast-flowing streams. The Snuffbox has suffered a 60% reduction in its former range in North America. Shells found in the Ausable River indicate that the Snuffbox once occupied a long reach of the river; however, recent surveys have turned up only a single live Snuffbox in the lower river.
*ENDANGERED* (Last examined by COSEWIC in 2001)

Reason for Designation: Declines in extent of occurrence, area of occupancy and number of extant locations; total population extremely fragmented, all four extant sites in one river (Sydenham River); entire population could be eliminated by a single upstream catastrophic event. Habitats already exposed to high silt loading from agricultural practices and pollution from point and non-point sources.

Status History: Designated Endangered in May 2001.

Kidneyshell
(Ptychobranchus fasciolaris)
The Kidneyshell is a medium-sized mussel that has a yellow-brown shell with thick, interrupted green rays. This mussel is found in small- to medium-sized rivers with strong flows, where it is often found deeply buried in firmly packed sand/gravel substrates in riffle areas. The Kidneyshell has been lost from over 70% of its historical range in Canada. The population in the Ausable River may be the healthiest remaining population in Canada.
*ENDANGERED* (Last examined by COSEWIC in 2003)

Reason for Designation: This species has been lost from about 70% of its historical range in Canada due to impacts of the Zebra Mussel and land use practices. It is now restricted to the East Sydenham and Ausable rivers. Although both populations appear to be reproducing, there is evidence that abundance has declined in the East Sydenham River. Agricultural impacts, including siltation, have eliminated populations in the Grand and Thames Rivers, and threaten the continued existence of this species in Canada.

Status History: Designated Endangered in May 2003. 

Rainbow - Information to be posted shortly.

*ENDANGERED* (Last examined by COSEWIC in 2006)

 

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.

Status History: Designated Endangered in April 2006.

 

Mapleleaf - Information to be posted shortly.

*THREATENED* (Last examined by COSEWIC in 2006)

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.

Status History: Designated Threatened in April 2006.

Fish Species at Risk in the Ausable River

Reptile Species at Risk in the Ausable River