Assessed June 2010 by COSSARO as Endangered

Part 1: COSSARO Candidate Species at Risk evaluation form – June 2010

Northern Riffleshell (Epioblasma Torulosa)

Current designations:

GRANKG2; last reviewed 18 Mar 2009
NRANK Canada – N1; last reviewed 12 Jun 2000
COSEWIC ― Endangered; 1999; Reassessed as Endangered in April 2010.
SARA – Schedule 1, 2005
General Status Canada – At Risk
ESA 2007 – Endangered 2008
SRANKS1
General Status Ontario – Endangered

Distribution and status outside Ontario:

Apparently the only populations in the US showing good evidence of recruitment occur in the Allegheny and Ohio River systems of Pennsylvania (COSEWIC 2010). The species also occurs in a few scattered watersheds in Michigan, West Virginia, Ohio and Kentucky. It is extirpated in Illinois and Indiana.

Eligibility criteria

Native status

Yes. The species occurs in the Midwestern United States and southwestern Ontario.

Taxonomic distinctness

Yes. Three subspecies have been recognized for the Northern Riffleshell but two are already extinct (Williams et al. 2008).

Designatable units

E.t. rangiana is the only extant subspecies and there is no evidence to suggest that individuals in Ontario belong to more than one designatable unit.

Priority-setting criteria

Recent arrival

No

Non-resident

No

Primary criteria (rarity and declines)

  1. Global rank

    Endangered – G2 Global Rank.

  2. Global decline

    Endangered – Historically, this mussel was found in Illinois, Indiana, Kentucky, Michigan, Ohio, Pennsylvania, West Virginia and Ontario, and possibly New York. Over the past century there has been a long-term range reduction of more than 95% with only four known populations remaining today]. The species has been extirpated from Illinois and Indiana (COSEWIC 2010; NatureServe 2010). Severe short-term declines of more than 70% have been occurring to populations in the United States (Nature Serve 2010).

  3. Northeastern North America ranks

    Endangered – Identified as S1, S2, SH or SX in 8 of 8 jurisdictions (100%).

  4. Northeastern North America decline

    Endangered – Similar to above, populations in northeastern North America have either been extirpated or are undergoing relative steep declines (95% long-term and >70% short-term), with only four reproducing populations remaining (COSEWIC 2010).

  5. Ontario occurrences

    Threatened – There are 9 extant element occurrences of northern Riffleshell in Ontario, and four historical EOs, qualifying this species for threatened status under this criterion. However, this species currently only occurs in two rivers in southwestern Ontario: Sydenham and Ausable (COSEWIC 2010). This species was thought to be extirpated from Canada, but populations in Sydenham and Ausable Rivers were re- discovered in 1997 and 1998, respectively. Their densities are estimated to be considerably lower than extant populations in Pennsylvania; only two of the sites in the Sydenham River surpassed threshold of 0.13 m2 required for successful recruitment (Crabtree and Smith 2009). Only the Sydenham population is demonstrating any evidence of recruitment (COSEWIC 2010).

  6. Ontario decline

    Endangered – Decline of > 75% of its former range in Ontario, much of this decline has occurred in the last 20 years as it no longer occurs in Lake Erie, Lake St. Clair and Detroit River, and possibly the Thames River. While the re-discovery of populations in Ontario indicates some recovery, the populations are still very low (COSEWIC 2010).

  7. Ontario’s conservation responsibility

    Endangered – Believed that this species has relatively healthy reproducing populations at only three locations: one in Ontario and the other two in Pennsylvania (COSEWIC 2010). The Ausable River population also shows some evidence of recruitment while many of the other US populations do not (COSEWIC 2010). Historically Ontario contained less than 10% of the species range but now provincial populations may comprise a much higher proportion of the global population and be critical to survival of the species.

Secondary criteria (threats and vulnerability)

  1. Population sustainability

    Not sufficient information- Of the remaining two Ontario populations, Sydenham River is showing no signs of decline while empty shells along Ausable River and small number of live individuals indicate that significant population declines have occurred recently. Because there is little idea of population size and trends, no quantitative analyses re population sustainability have been undertaken.

  2. Lack of regulatory protection for exploited wild populations

    Not in any category. The Northern Riffleshell is protected under the Endangered Species Act, 2007 and the federal Species at Risk Act. The Fish and Wildlife Conservation Act regulates harvests of molluscs.

  3. Direct threats

    Endangered – The primary cause of the disappearance of Northern Riffleshell populations on Lake Erie, Lake St. Clair and Detroit River is thought to be the spread of exotic mussels. Northern Riffleshell was abundant in Detroit River but declined rapidly from 1992 to 1994 as a result of invasion by Zebra and Quagga Mussels (Schloesser et al. 1998). It is also sensitive to sedimentation caused by heavily deforested and cultivated watersheds. Sedimentation and degraded water quality are the main concerns in the two watersheds where the species still occurs.

  4. Specialized life history or habitat-use characteristics

    Endangered – The Northern Riffleshell primarily occurs at clear, well oxygenated riffles on small rivers and therefore is highly specialized. The larval stage is dependent on the presence of host fish species sculpins and darters.

Cossaro Criteria Met (Primary/Secondary)

  • Endangered – [6/2]
  • Threatened – [1/0]
  • Special concern – [0/0]

Recommended Status: Endangered

Summary

This species is currently confined to well-oxygenated riffle runs on two rivers in 3 southwestern Ontario. These are two of four extant populations in North America. The population is currently stable on one river, but there is evidence of recent declines on the other. Sedimentation, declining water quality, and the rapid spread of invasive mussels are the main threats in the intensively cultivated watersheds. The species has already disappeared from several areas in its former range, largely because of the spread of invasive Zebra Mussel (Dreissena polymorpha) and Quagga Mussel (Dreissena rostriformis bugensis). Because of the small area of occupancy and continuing declines in population and quality of habitat, this species is Endangered in Ontario.

Information sources

Canadian Endangered Species Conservation Council (CESCC). 2006. Wild Species 2005: The General Status of Species in Canada. http://www.wildspecies.ca/wildspecies2005/index.cfm?lang=e. (Accessed: May 18, 2010) [link inactive]

COSEWIC. 2010. COSEWIC 2-month interim status report on the Northern Riffleshell (Epioblasma torulosa rangiana) in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa, Ontario. vi + 35 p. Crabtree, D.L. and T.A. Smith. 2009. Population attributes of an endangered mussel, Epioblasma torulosa rangiana in French Creek and implications for its recovery. Northeastern Naturalist 16:339-354.

NatureServe. 2010. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia. Available. (Accessed: May 18, 2010).

Schloesser, D.W., W.P. Kovalak, G.D. Longton, K.L. Ohnesorg, and R.D. Smithee. 1998. Impact of Zebra and Quagga Mussels (Dreissena spp.) on Freshwater Unionids (Bivalvia: Unionidae) in the Detroit River of the Great Lakes. American Midland Naturalist 140:299-313.

Williams, J.D., A.E. Bogan, and J.T. Garner. 2008. Freshwater mussels of Alabama and the Mobile Basin in Georgia, Mississippi, and Tennessee. University of Alabama Press, Tuscaloosa, Alabama.

Appendix 1

Northeastern North America rank, status and decline

RegionRank
CTNot present
DENot present
ILSX
INSX
IANot present
KYS1
LBNot present
MANot present
MBNot present
MDNot present
MENot present
MIS1
MNNot present
NBNot present
NFNot present
NHNot present
NJNot present
NSNot present
NYNot present
OHS1
ONS1
PAS2
PENot present
QCNot present
RINot present
VANot present
VTNot present
WINot present
WVS1

Occurs as a native species in 8 of 29 northeastern jurisdictions SRANK or equivalent information available for 8 of 8 jurisdictions = (100%) S1, S2, SH, or SX in 8 of 8 = (100%)

Part 2: Ontario evaluation using COSEWIC criteria

Regional (Ontario) COSEWIC criteria assessment

Criterion A – declining population

No The number of mature individuals appears to be stable at present in Sydenham River. However, presence of empty shells indicates that Ausable River population was considerably larger formerly.

Criterion B – small distribution and decline or fluctuation

Yes. Both the EO (983 km2) and IAO (296 km2) are within the thresholds for Endangered (< 5,000 km2 and < 500 km2, respectively). As the species is found at only 2 locations, sub-criterion "a" (no. of locations ≤ 5) is applicable. There is a continuing decline inferred in the quality of habitat so sub-criterion "b(iii)" also is applicable.

Criterion C – small population size and decline

No. Does not meet criterion. The total number of mature individuals is estimated to be 146,400, above the thresholds for this criterion (< 10,000 for threatened), although one of the two populations contains 89% of the total estimated population.

Criterion D – very small or restricted

Yes. Meets the criteria for Threatened as the species is found at fewer than 5 locations and while it is prone to the effects of human activities (e.g., degraded water quality from agriculture, industrial, and urban activities), these activities are not occurring over a very short time frame in an uncertain future.

Criterion E – quantitative analysis

No. None conducted.

Rescue effect

No. Immigrants would be adapted to survive in Ontario. Species has limited dispersal ability and no longer occurs in immediately adjacent waters in US. Rescue is unlikely.