Science Advisory Report 2013/069
Recovery Potential Assessment of Lilliput (Toxolasma parvum) in Canada
Summary
- In Canada, the current and historic known distribution of Lilliput is limited to nine confirmed populations, one of which is currently considered to be extirpated. Extant populations include four tributaries of Lake St. Clair (East Sydenham, Thames, Belle and Ruscom rivers), Grand River (Lake Erie drainage), Welland River (tributary of the Niagara River), Jordan Harbour (a wetland at the mouth of Twenty Mile Creek) and Hamilton Harbour and surroundings (Cootes Paradise, Carroll’s Bay, Grindstone Creek, Sunfish Pond; Figure 1).
- Lilliput glochidia must encyst on the gills of an appropriate host fish to survive and metamorphose. The putative host fishes for Lilliput in Canada are Johnny Darter (Etheostoma nigrum), Green Sunfish (Lepomis cyanellus), White Crappie (Pomoxis annularis) and Bluegill (Lepomis macrochirus). This is supported by laboratory infestation experiments and direct distributional overlap between each of these four fish species and Lilliput known distribution in Canada.
- Although Lilliput is found in a variety of habitats (e.g., small rivers, larger rivers, wetlands, shallow areas of ponds and backwaters), it is mostly commonly found in the lower reaches of large rivers, wetlands, and backwater areas with little current.
- Based on what is known of Lilliput life history (probable low fecundity, short lifespan, early maturity) previous modeling of Unionid mussels suggests that, compared to other Unionid species, Lilliput 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 Lilliput populations in Canada are largely attributed to the presence of contaminants and toxic substances in their environment, 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 Lilliput 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 investigate to inform modelling efforts.
This Science Advisory Report is from the September 24, 2013 Recovery Potential Assessment of Lilliput (Toxolasma parvum). 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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