Science Advisory Report 2010/073

Recovery Potential Assessment of Eastern Pondmussel (Ligumia nasuta), Fawnsfoot (Truncilla donaciformis), Mapleleaf (Quadrula quadrula), and Rainbow (Villosa iris) in Canada

Summary

• Eastern Pondmussel is known to be currently distributed in Long Point Bay, Lyn Creek and the St. Clair River delta. It is currently unknown whether reproducing populations are present at Beaver Lake or in the Grand River. It is believed that Eastern Pondmussel has been extirpated from the Great Lakes and their large connecting channels.
• Fawnsfoot currently occupies the Grand, Sydenham and Thames rivers. A single individual has been discovered at both the Saugeen River and the St. Clair River delta. Fawnsfoot is thought to be extirpated from the Great Lakes and their large connecting channels.
• The Canadian distribution of Mapleleaf is divided into two designatable units (DUs): Great Lakes - Western St. Lawrence population (Ontario DU) and the Saskatchewan - Nelson population (Manitoba DU). In Ontario, Mapleleaf are present in the Ausable, Grand, Ruscom, Sydenham, Thames and Welland rivers, as well as Jordan Harbour. A single individual has been recorded from both the Bayfield River and the St. Clair River delta. In Manitoba, Mapleleaf is known to currently occupy the Assiniboine River but the presence of a reproducing population is unknown from all other rivers.
• It is known that Rainbow occupies the Ausable, Bayfield, Grand, Maitland, Moira, Saugeen, Sydenham, Thames and Trent rivers, as well as the St. Clair River delta. It is currently unknown if a Rainbow population is present in the Salmon River.
• Gills of the appropriate host fish are the required habitat for the glochidial life stage of all species.
• Adult Eastern Pondmussel preferred habitat includes both nearshore, sheltered areas of the Great Lakes as well as the slack water of slow-moving rivers.
• Adult Fawnsfoot are generally found in medium- to large-sized rivers at depths ranging from less than 1 m to greater than 5 m.
• The current distribution of adult Mapleleaf in Canada indicates that this species tends to occur in the lower reaches of medium to large rivers. Water flow does not appear to be limiting factor for Mapleleaf as it has been found in both slow- and fast-flowing rivers.
• Although historically Rainbow were present in the nearshore area of the Great Lakes and its connecting channels, Zebra Mussel introduction has restricted this species to small creeks and rivers, and the St. Clair River delta. In river systems it can be found in the middle to upper reaches in or near riffles, and is generally found in areas with moderate to strong current.
• The sensitivity of population growth of freshwater mussels to perturbation can be predicted using life history characteristics.
• Population growth of freshwater mussels is particularly sensitive to the survival of adult and settled juvenile mussels.
• Fawnsfoot population growth is more susceptible to changes in reproductive traits (age at maturity, fecundity and glochidial survival) than are Mapleleaf, Eastern Pondmussel, or Rainbow.
• Uncertainty surrounding life-history estimates is highest for survival of glochidia and early juveniles. Rates of host infestation, and the influence of host density on these rates, are particularly understudied.
• The greatest threat to the survival and persistence of freshwater mussels is attributed to the introduction and establishment of dreissenid mussels and decreases in the quality of available freshwater mussel habitat. In addition, there is evidence that decreases in water quality, specifically increased turbidity and suspended solids, increased nutrient loading, and increased levels of contaminants and toxic substance are also limiting the distribution of freshwater mussels. Additional threats include altered flow regimes and the removal and alteration of habitat. Due to the obligate nature of the mussel reproductive cycle, any threat leading to the separation of mussel and host fish during reproduction can be detrimental to the mussel population. Secondary threats include predation and harvesting, and recreational activities.
• There remain numerous sources of uncertainty related to life history, juvenile habitat requirements, host distribution and abundance, and host-mussel distribution overlap for these freshwater mussels. A thorough understanding of the threats affecting the decline of freshwater mussel populations is also lacking. Numerous modeling parameters specific to these freshwater mussels are currently unknown, such as glochidial survival, juvenile survival, and population growth rates. Little is known of the relationship between the host population density and the frequency of host-mussel encounters.

Complete document (PDF, 650 KB)

Accessibility Notice

This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.