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Recovery Strategy for Nooksack Dace
Identification of Critical Habitat
Critical habitat is defined in SARA as “the habitat that is necessary for the survival or recovery of a listed wildlife species and that is identified as the species’ critical habitat in the recovery strategy or in an action plan for the species.” [SARA S. 2(1)]. Critical habitat for Nooksack dace has not been formally described in this recovery strategy, though the Recovery Team has compiled scientific data which will assist in the scientific definition of critical habitat, including a separate assessment of the habitat requirements of the species(National Recovery Team for Salish Sucker and Nooksack Dace 2005). Specific features of critical habitat for Nooksack dace are summarized below. This information should provide the basis for an official designation of critical habitat through the action planning process, which will include socioeconomic analysis and consultation with affected interests. Defining critical habitat will contribute to the refinement of recovery objectives and the management of activities that impact the species.
Critical Habitat Features
Based on available physical and biological data, Nooksack dace critical habitat could include the following key elements:
The Reach Scale
Riffles and shallow pools (see below) are the required habitats of Nooksack dace, but critical habitat should be defined at the reach scale, a larger, natural unit of river morphology that ranges from hundreds to thousands of metres in length (Frissell et al. 1986). There are three reasons for adopting this scale. First, the reach scale corresponds to the distribution of subpopulations within watersheds (Pearson 2004a). Second, the ‘channel units’ of critical habitat (riffles and shallow pools) are dynamic and frequently move during flood events in these streams. In Bertrand Creek, this occurs on an annual basis (Pearson pers. obs.). Effective protection and management of critical habitat in these circumstances must allow for normal channel processes and must, therefore, occur at a spatial scale larger than the channel unit. The reach scale is the next largest in accepted stream habitat classifications (Frissell et al. 1986; Imhof et al. 1996). Third, the reach scale corresponds most closely to that of land ownership in these watersheds and, consequently, to most potential recovery actions.
Available information overwhelmingly suggests that riffles are critical to species persistence. Nooksack dace typically occur in riffles over loose gravel and cobble substrates where water velocity exceeds 0.25 m.s-1. They spawn near the upstream end of riffles (McPhail 1997)between late April and early July (Pearson 2004a)and forage nocturnally for riffle dwelling insects (McPhail 1997). The percent of riffle in a stream reach is a good predictor of dace presence. Riffles that are isolated by long stretches of deep pool, however, are seldom inhabited (Pearson 2004a). A threshold of 10% riffle by length would exclude these small isolated riffles that have little value to Nooksack dace.
Shallow Pool Habitat
Young-of-the-year Nooksack dace inhabit shallow (10-20 cm) pools adjacent to riffles where they swim above sand, mud, or leaf litter substrates and feed upon chironomid pupae and ostracods (McPhail 1997). Loss of these habitats will quickly produce population-level impacts.
Riparian vegetation should be included in critical habitat to the extent it is necessary to protect the integrity of in-stream critical habitat. Required widths would vary among sites and should be defined in reach scale assessments. Reserves must be sufficient to control sediment entry to the stream from overland flow, to prevent excessive bank erosion and to buffer stream temperatures. Reserve areas will also remove significant amounts of nitrate and phosphorous from groundwater, although their efficiency depends strongly on hydrogeologic conditions (Martin et al. 1999; Puckett 2004; Wigington et al. 2003). The effectiveness of a riparian reserve in preventing materials (e.g., sediments, nutrients, toxins) from entering a stream depends strongly on its continuity in addition to its width (Weller et al. 1998). Consequently, riparian reserves in critical habitat reaches should be continuous. In open landscapes, such as agricultural fields, vegetation from reserve areas will collect windblown insects (Whitaker et al. 2000). Such insects, falling from riparian vegetation into the water constitute an important food source in headwater streams (Allan et al. 2003; Schlosser 1991).
It is important to understand that in some circumstances, more than 30 m of riparian vegetation may be required for full mitigation of warming (Brown & Krygier 1970; Castelle et al. 1994; Lynch et al. 1984) and siltation (Davies & Nelson 1994; Kiffney et al. 2003; Moring 1982), and for long-term maintenance of channel morphology (Murphy et al. 1986; Murphy & Koski 1989). At least 10 m are required to maintain levels of terrestrial food inputs similar to those of forested landscapes (Culp & Davies 1983). Reserves as narrow as 5 m provide significant protection from bank erosion and sediment deposition from overland flow (Lee et al. 2003; McKergow et al. 2003).
Failure to maintain an adequate riparian reserve as part of critical habitat would be highly likely to cause population-level impacts. In habitats lacking sufficient flow or groundwater sources, lack of shade may increase water temperatures to harmful levels. Increased erosion due to poorer bank stability will cause sediment deposition in riffles, impairing spawning and incubation, reducing food availability, and eliminating the interstitial spaces in coarse substrate that dace occupy. Nutrient loading will be higher in reaches without adequate riparian vegetation (Dhondt et al. 2002; Lee et al. 2003; Martin et al. 1999) and is likely to contribute to hypoxia through eutrophication. Solar radiation will also be higher in reaches lacking adequate riparian shading (Kiffney et al. 2003)and will contribute to eutrophication. Reserves of 30 m or more should be maintained around Nooksack dace habitat wherever feasible to provide a high level of protection from impacts of adjacent land uses.
Schedule of Studies to Identify Critical Habitat
Information exists to assist in the definition of critical habitat for Nooksack dace throughout its presently known range. Further surveys are required to identify other potential populations and characterize their critical habitats, as summarized below:
|Population Identification||The Coquitlam and Alouette Rivers are suspected of containing Nooksack dace based on a preliminary genetic and morphometric study of their R. cataractae populations (J.D. McPhail, UBC, unpubl. data). Additional samples are required for confirmation.||2005-2006||Underway|
|Critical Habitat Surveys||Habitat in the BrunetteRiverhas not been surveyed as its populations were unknown prior to 2004. Surveys will also be required in the Coquitlam and Alouette Rivers if the presence of Nooksack dace is confirmed there.||2006-2007||Planned|
Knowledge Gaps in Nooksack Dace Biology
Additional studies should be conducted to address the following data needs related to specific threats to Nooksack dace. This information will contribute to the protection of Nooksack dace and their critical habitats.
|Impacts of Riffle Drying||The fate of dace in reaches that dewater during late summer is uncertain. Sampling during this period will resolve whether fish leave the reach, move into pools, burrow into substrate, or die.||2004-2005||Underway|
|Impacts of Sediment Deposition in Riffles||The extent to which sediment deposited in riffles affects their ability to support healthy dace populations is uncertain and needs to be quantified.||2007-2008||Need Identified|
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