Science Advisory Report 2013/046
Recovery potential assessment of Rocky Mountain Sculpin (Cottus sp.), Eastslope populations, in Alberta
Summary
- In Alberta, Rocky Mountain Sculpin is known to occur in the St. Mary River system above the St. Mary Reservoir and in lower portions of Aetna and Lee creeks; in the North Milk River; and in the Milk River upstream of its confluence with the North Milk River and downstream of the confluence to within 85 km of the Montana border.
- There is insufficient information to identify Rocky Mountain Sculpin in the six waterbodies as genetically-discrete populations. Currently there are no barriers to movement within the St. Mary River system or within the Milk River system; only downstream movement is possible from the St. Mary River system to the Milk River system, by means of the St. Mary Canal. In this assessment each waterbody is referred to as a stock rather than a population.
- This species occupies cool, clear headwater rivers and tends to be more common in silt-free rocky substrates near stream margins with low to moderate water velocities.
- During spawning, nests are constructed under rocks or sometimes on aquatic vegetation or instream debris; the male remains near the nest for several weeks keeping it clean of silt and other debris until the eggs hatch. The nest meets the SARA definition of residence.
- No estimates of abundance have been obtained to date but repetitive sampling at some sites allows comparisons between stocks. The status of Rocky Mountain Sculpin is Good for the St. Mary and North Milk rivers, Fair for the Milk River below the confluence, Poor for the Milk River above the confluence and Unknown for Lee and Aetna creeks.
- A Minimum Viable Population (MVP) of at least 1,480 adults was estimated when the probability of extinction was 0.01 over 100 years, the probability of catastrophic (50%) decline was 0.15, and the extinction threshold was two adults (one female and one male). A population of this size was predicted to require 0.12 ha of suitable habitat.
- A MVP of 1,480 adults was predicted to go extinct in 42 years (range: 25-68). When survival of all ages was improved by 20%, the population began to grow, and the risk of imminent extinction was eliminated.
- The dynamics of Rocky Mountain Sculpin populations are particularly sensitive to perturbations that affect the survival of immature individuals (from hatch to age-2) and the collective survival of adults (ages 2-8).
- The greatest threat to the survival and persistence of Rocky Mountain Sculpin in Alberta is habitat degradation and loss, especially as a result of flow alteration. Drought conditions in combination with water regulation and extraction have the potential to significantly reduce the quantity and quality of sculpin habitat.
- There remain numerous sources of uncertainty related to Rocky Mountain Sculpin: life history and biological characteristics including young-of-the-year and juvenile survival rates, population growth rates and seasonal movements; habitat requirements particularly for eggs and fry and for overwintering; 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 22-23, 2011, Regional Recovery Potential Assessment of Rocky Mountain Sculpin. Additional publications from this process will be posted as they become available on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule.
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