Science Advisory Report  2013/041

Recovery Potential Assessment of Hickorynut (Obovaria olivaria) in Canada

Summary

• In Canada, the current and historic known distribution of Hickorynut is limited to four confirmed populations, one of which is currently considered to be extirpated. Extant populations include the Mississagi River (Lake Huron drainage), the Ottawa River and its tributaries (Coulonge River), and the St. Lawrence River and its tributaries (Assomption River, Saint-Francois River and Batiscan River; Figure 1).
• Hickorynut glochidia must encyst on the gills of an appropriate host fish to survive and metamorphose. The putative host fish for Hickorynut in Canada is Lake Sturgeon (Acipenser fulvescens). This is supported by laboratory infestation experiments and a direct overlap in the distribution of the two species.
• Adult Hickorynut habitat is generally described as sand or mixed sand gravel substrate in relatively deep water with moderate to fast water velocity in large river systems.
• It appears that the greatest limiting factors to the stabilization and growth of Hickorynut populations in Canada are largely attributed to the introduction and establishment of dreissenid mussels and decreases in the quality of available habitat. In addition, due to the obligate glochidial encystement stage, Hickorynut is also directly affected by host fish abundance and indirectly by the threats affecting the host fish.
• If the host species abundance is not limiting, Hickorynut population growth is most sensitive to perturbations that affect adult and juvenile survival, moderately sensitive to the age at maturity, and relatively insensitive to proportional changes in glochidial survival, fecundity, or maximum age. If host abundance is limiting, Hickorynut viability becomes sensitive to the rate of glochidial attachment.
• Given a stable host abundance and a growing mussel population, the expected mussel abundance can be calculated using the mussel life history parameters.
• Mussel population abundance was very sensitive to the availability of juvenile hosts, and much less sensitive to the availability of adult hosts.
• A number of key sources of uncertainty exist for this species related to population distribution, structure, habitat preferences and to the factors limiting their existence. Specifically, there is a need for a continuation of quantitative sampling to confirm the current population status assessment, and to determine population sizes. As Hickorynut is often found in deeper water, additional experimental sampling methods should be investigated to sample these deep-water habitats. Supplementary laboratory experiments, and if feasible, field experiments should be completed to determine if Lake Sturgeon is indeed the host fish for Hickorynut in Canada.

This Science Advisory Report is from the January 29-30, 2013 Recovery Potential Assessment of Hickorynut (Obovaria olivaria). 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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