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Recovery Strategy for Nooksack Dace
1. Are individuals capable of reproduction currently available to improve the population growth or population abundance?
Yes. Breeding adults have been captured recently from all populations.
2. Is sufficient habitat available to support the species or could it be made available through habitat management or restoration?
Yes. Sufficient physical habitat exists to support the three populations that have been surveyed (Bertrand, Pepin and Fishtrap creeks), although up to 70% of it is seriously degraded by sediment deposits or low water levels in late summer. The severity and extent of these problems could be mitigated by reducing ground and surface water withdrawals during sensitive periods, by reducing sediment entry to streams and by managing beaver activity in sensitive habitats. The quantity and condition of available habitat in the Brunette River population is unknown at present.
3. Can significant threats to the species or its habitats be avoided or mitigated through recovery actions?
Yes. Riffle degradation through seasonal drying can be avoided by reducing water withdrawals or flow supplementation. Sedimentation can be reduced through riparian planting, improved agricultural practices, the installation of sediment traps in storm sewer systems, and proper sediment control at mine and construction sites. Riffle loss can be mitigated through habitat restoration and (when necessary) beaver control.
4. Do the necessary recovery techniques exist and are they demonstrated to be effective?
Yes. Techniques to reduce problems of low base flow, sediment deposition and beaver ponding are well known. Monitoring of created riffle habitat has demonstrated that restored habitats are quickly colonized.
Recovery of Nooksack dace populations to levels ensuring long-term survival is both technically and biologically feasible. However, it is highly likely the species will remain at some risk due to the continued pressure on its habitats from a rapidly growing human population in the Fraser Valley.
Recovery will involve the establishment and/or maintenance of riffle habitat sufficient to maintain a population in each creek. Some management will be required in all three watersheds. It should focus on in-stream flow protection in Bertrand Creek, restriction of beaver impoundment in Pepin Brook, and the restoration of riffle habitat in Fishtrap Creek. Appropriate recovery actions in the Brunette River are unknown pending population and habitat status surveys.
Recovery Goal, Objectives and Corresponding Approaches
To ensure the long-term viability of Nooksack dace populations throughout their natural distribution in Canada.
|Watershed||Habitat with High Potential Productivity Occupied in 2004 (km)||Total Habitat with High Potential Productivity (km)|
A significant portion of habitat with high potential productivity is not currently occupied, primarily due to riffle degradation or loss to drying, sediment deposition and beaver impoundment. Achievement of interim population recovery targets in the three surveyed watersheds will require that all habitat with high potential productivity be occupied (see objective 2 below). In most cases unoccupied areas could be rendered habitable quickly by increasing water flow, controlling beaver, and/or implementing fish-sensitive drainage maintenance practices.
|Watershed||Area of Riffle in Potential Habitat Reaches (m2)||Population Target (excludes young of year)|
|Brunette River||unknown||unknown pending habitat survey|
*Assumes an average density of 1.9 Nooksack dace per m2 riffle in suitable habitat (Inglis et al. 1994). Rounded to nearest hundred.
**Based on 1999 survey. By 2001 approximately 200 m2 of riffle was lost to beaver ponding (Pearson 2004a).
Ideally population targets would be based on robust population viability analyses. Unfortunately the necessary demographic data is lacking for Nooksack dace. An appropriate guideline for minimum viable population (MVP) size in vertebrate species, based on an extensive review of the scientific literature (Reed et al. 2003, Thomas 1990), is 7000 breeding adults (median value; range 2000-10000). This abundance is considered adequate to maintain genetic diversity and to buffer the population from random variations in survival, and thus to maintain long-term viability in the absence of deterministic factors causing the population to decline.
Populations of Nooksack dace in each of the four watersheds are essentially independent of one another, with extremely low probability of natural exchange of individuals between watersheds because of the very large distances of unsuitable habitat that separate populations. Natural recolonization of habitat from which a population has been extirpated (rescue effect) is therefore highly unlikely. Each watershed, consequently, warrants a separate recovery target in the low to mid thousands.
High quality habitat in Bertrand Creek supported an average of 1.9 dace/m-2 (n=20, SE = 0.35) in the single available direct estimate of density (Inglis et al. 1994). If all riffle areas in all reaches with habitat with high potential productivity supported this density, total adult abundance would be in the low thousands for each watershed. This suggests that for Nooksack dace in the three surveyed watersheds, the maximum achievable population size is close to the minimum viable population size and that all suitable habitats should be designated critical.
3. To ensure that at least one reach in each watershed supports a high density of Nooksack dace.
Within each watershed, individual populations may be structured as metapopulations, with different subpopulations separated by poor quality habitat, and some level of exchange of individuals between sub-populations. Population persistence in such systems is dependent upon the existence if one or more source areas where population growth is positive and densities are high.
Draft Policy on the Feasibility of Recovery, Species at Risk Act Policy. January 2005.
- Date Modified: