Science Advisory Report 2013/063

Recovery potential assessment of Western Silvery Minnow (Hybognathus argyritis) in Canada

Summary

• Western Silvery Minnow is known to occur in the Milk River system, in Alberta, a tributary of the Missouri River in Montana.
• In the Milk River system, adult Western Silvery Minnow inhabit small to large low-gradient rivers, with backwater areas, and shallow flat and run habitats. Little is known about overwintering habitat requirements. Spawning occurs in turbid, sediment-laden water of moderate flow.
• The abundance of this species in the Canadian portion of the Milk River generally increases (from Low to High) with distance downstream but population trend is Unknown, thus overall population status is currently Unknown.
• A Western Silvery Minnow population with persistence probability of about 0.01 over 100 years and extinction threshold of two adults, experiencing a 0.15 probability of catastrophic (≥ 50%) decline per generation, would require a Minimum Viable Population (MVP) of 12,000 adults and 25 ha of suitable habitat. Using an extinction threshold of 50 adults, would require a MVP of 236,000 adults and 497 ha of suitable habitat.
• In the absence of additional harm, recovery efforts or habitat limitations, it would take a growing Western Silvery Minnow population approximately nine years to reach the MVP of 12,000 adults if starting from a population of 1,200 adults.
• Western Silvery Minnow is particularly sensitive to perturbations to early life survival, and to fecundity of first time spawners, thus the best strategy for recovery is to improve survival of immature individuals.
• The greatest threats to the survival and persistence of Western Silvery Minnow in Alberta are those that alter the natural flow regime of the river causing habitat loss or impairment. Drought and anoxic conditions in combination with water regulation and extraction have the potential to significantly reduce the quantity and quality of minnow habitat.
• There remain numerous sources of uncertainty related to Western Silvery Minnow: life history and biological characteristics including population growth rate and abundance; habitat requirements, including the distribution and extent of suitable habitat, overwintering requirements, and spawning requirements; the frequency and magnitude of catastrophic events and true extinction thresholds; and an understanding of the environmental factors that limit their existence.

This Science Advisory Report is from the March 25-26, 2011, Recovery Potential Assessment of Western Silvery Minnow. 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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