Science Advisory Report  2014/014

Recovery Potential Assessment of Threehorn Wartyback (Obliquaria reflexa) in Canada

Summary

• In Canada, the current and historic known distribution of Threehorn Wartyback (Obliquaria reflexa)is limited to five confirmed populations, one of which is currently considered to be extirpated. Extant populations include two tributaries of Lake St. Clair (Sydenham, and Thames rivers), and the Grand River (Lake Erie drainage; Figure 2).
• Threehorn Wartyback glochidia must encyst on the gills of an appropriate host fish to survive and metamorphose. The putative host fishes for Threehorn Wartyback in Canada include Common Shiner (Luxilus cornutus) and Longnose Dace (Rhinichthys cataractae). This is supported by laboratory infestations in the United States (as infestation experiments have not occurred with Canadian Threehorn Wartyback), and distributional overlap of known ranges in Canadian waters.
• Threehorn Wartyback is most commonly found in large rivers with stable gravel, sand and mud substrates with moderate current; however, it may also be found in shallow embayments and reservoirs with almost no current.
• Based on what is known of Threehorn Wartyback life history (low fecundity, short lifespan, relatively early maturity) previous modeling of Unionid mussels suggests that, compared to other Unionid species, Threehorn Wartyback is expected to be most sensitive to perturbation or uncertainty in juvenile survival, adult survival, and lifespan, and relatively insensitive to changes in glochidial survival, fecundity, or age at maturity.
• It appears that the greatest limiting factors to the stabilization and growth of Threehorn Wartyback populations in Canada are largely attributed to the presence of contaminants and toxic substances in their environment, habitat removal and alteration, and the introduction and establishment of various invasive species.
• A number of key sources of uncertainty exist for this species related to population distribution, population structure, habitat preferences and to the factors limiting their existence.
• Specifically, there is a need for a continuation of quantitative sampling to inform the population status assessment. There is a need for exploratory sampling in systems with habitat characteristics similar to those areas where Threehorn Wartyback is known to occur. To confirm host fishes in Canada, there is a need to complete laboratory, and if feasible field experiments. Many life history characteristics required to inform population modelling efforts are currently unknown for this species and should be investigated to inform modelling efforts.

This Science Advisory Report is from the December 10, 2013 Recovery Potential Assessment of Threehorn Wartyback (Obliquaria reflexa). Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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