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COSEWIC Assessment and Update Status Report on the Nooksack dace in Canada


Habitat Requirements

R. cataractae are widely known as stream riffle specialists (Facey and Grossman, 1992; Gibbons and Gee, 1972; Thompson et al., 2001; McPhail, 1997). Adult densities are highest in depths of 10 to 20 cm, at water velocities greater between 20 and 35 cm/s, over loose gravel, cobble or boulder substrates (Inglis et al., 1994; McPhail, 1997). Overwintering Nooksack adults have been found beneath cobble substrate in fast flowing riffles (Pearson, unpubl. data). Nooksack dace typically spawn at the upstream end of riffles and young-of-the-year occupy shallow (10-20 cm), calm, pools over fine substrates at the downstream end of riffles (McPhail, 1997).

The proportion of riffle habitat in a stream reach is the strongest predictor of Nooksack dace presence. They are rarely found in reaches with less than 10 percent riffle by length, or in reaches where long stretches of deep pool habitat separate riffles (Pearson, 2004). Natural habitat fragmentation occurs where low stream gradient precludes riffle formation and where beaver ponding converts riffles to pools. Anthropogenic fragmentation, caused by channel dredging and seasonal lack of flow due to ground and surface water extraction, is also common in the Canadian range.

In Canada Nooksack dace are associated with small to moderate-sized channels (1-10 m in width), but this probably reflects available habitat in occupied watersheds rather than a preference (McPhail, 1997). On the Olympic Peninsula mean channel width at occupied sites was 45.2 m (range 14.9-76 m, n=12, Mongillo and Hallock 1997).

Habitat Trends

Streams in the Fraser Delta area typically have small watersheds, minimal low flows in July and August, and limited natural or artificial storage; some have significant water demands. Storage development, riparian zone management, and erosion control are all important issues (Rood and Hamilton 1994). 

The Brunette River is considered to have undergone significant alteration to its hydrological regime due to urbanization. In particular, the lower portion of the Brunette River is characterized by channelization and dyking, with no instream cover, high water temperatures and low dissolved oxygen (Rood and Hamiltion 1994).

The current extent of riffle habitats and occupancy in the Nooksack tributaries is well documented (Fig. 4; Pearson 1998a,b; Pearson 2004). The trend in its quantity and quality is clearly one of decline. At least some riffles in all three creeks are compacted by sediment from bank erosion and/or urban storm sewer effluent (Pearson, 2004). The mainstem of Fishtrap Creek was dredged for flood control by the City of Abbotsford in 1990-1991, eliminating most of its previously abundant riffle habitat (J.D. McPhail, pers. comm. 2006). In particularly dry years (e.g. 2002) flow ceases completely in some occupied reaches of Bertrand Creek, eliminating riffle habitat. Reaches with strongest baseflows still lose over 80% of riffle area relative to winter levels (Pearson, unpubl.). Aquifer draw-down by local wells is estimated to have reduced the creek’s baseflow by 24% since 1960 (Golder and Associates, 2004). Surface withdrawals for irrigation are also of water licences held in the Nooksack drainage is significant. These large-scale abstractions or diversions undoubtedly limit availability of nooksack dace habitat (riffles) in the low-flow summer months in some locations as all of these licences are run significant, but have not been quantified.

A number of river withdrawals occur during the dry periods for irrigation purposes. Bertrand, Fishtrap and Pepin creeks are all relatively small streams that begin to lose riffle habitat (width) when flows drop below 10% mean annual discharge (mad) and riffle quality (depth and velocity) when flows drop below 20% mad (mad; Ptolemy and Lewis 2003). In recent years (1984-2005), Betrand Creek in particular has seen 30-day summer flows as low as 1% mad (Ron Ptolemy, Standards and Guidelines Specialist, Ecosystems Branch, BC Ministry of Environment, Victoria, BC; personal communication 2007) Fishtrap Creek baseflows are also a concern with monitored flows averaging 10% mad and dropping to <1% mad in the 2003 drought. Pepin Creek flows in contrast are relatively healthy with baseflows averaging 24% mad and lows as >10% during drought periods (R. Ptolemy, pers. comm.).

Only crude estimates of habitat loss are possible, due to lack of baseline data (Table 3). They suggest that approximately half of the original riffle habitat from the Nooksack tributaries has been lost, most of it prior to 1996. Losses in the past 10 years appear to have been minimal, mostly due to beaver pond inundation of riffles in Pepin Creek (Pearson, 2004).

Table 3: Estimated Losses of Nooksack dace Habitat in Canada
 UnitsPepin CreekFishtrap CreekBertrand CreekBrunette River
Existing Area (from Table 1)(m2)2 0002 3003 00020 155
Losses to 1996(m2)
2 500
2 780
2 530
2 300
2 500
5 000
Losses since 1996(m2)*235000
Total Loss%575246?

Habitat was assumed to have comprised 20% of channel length in reaches known or believed to have lost substantial riffle area prior to 1996.

* measured by Pearson (2004)
** Areas calculated as product of mean wetted widths (from Pearson, 1998a) and 20% of reach length rounded to nearest 100 m2

Habitat Protection/Ownership

There is no known Nooksack dace habitat on federal or provincial lands, but approximately 2 km of occupied habitat in the Nooksack River tributaries (Table 4) and at least 5.2 km of suitable or occupied habitat in the Brunette River (Pearson unpubl. data) occur on regional or municipal parkland. This amounts to somewhat more than 10% of suitable habitat.

Virtually all of the remaining habitat is on private, urban or agricultural lands. There is limited legislative protection at present. The ‘harmful alteration, disruption or destruction’ of fish habitat, including that of Nooksack dace, is partially prohibited by the federal Fisheries Act (R.S.C. 1985, c. F-14, s. 35-36). The Species at Risk Act prohibits the destruction of habitat identified as critical in an approved recovery strategy or action plan (SARA, S.C.2002, c.29, s. 57-58), but the competent minister must make an order before the prohibitions apply.

All occupied or potential habitats in the Nooksack River tributaries (Fig. 4) are proposed by the Recovery Team for designation as critical habitat under SARA.

Table 4: Public Lands Bordering or Upstream of Occupied or Suitable Nooksack Dace Habitat in Canada
WatershedOwnershipDescriptionChannel Length Present/ Suitable/ OccupiedStatus/Comments
Pepin CreekGreater Vancouver Regional DistrictAldergrove Lake Regional Park4825 m Pepin Brook and tributaries; 1660 m occupiedRegional parkland
Bertrand CreekTownship of LangleyOtter Park225 m Bertrand Creek; 225 m occupiedMunicipal parkland; Extremely vulnerable to drying
Federal Government Dept. Nat. DefenceNaval Station Aldergrove2850 m Bertrand Creek; 0 suitableMilitary lands; Extreme headwaters
Township of LangleyVanetti Park175 m Bertrand Creek; 0 suitableMunicipal parkland; Upstream of suitable habitat
Township of LangleyCreekside Park185 m Bertrand Creek; 0 suitableMunicipal parkland
Fishtrap CreekCity of AbbotsfordGardner Park, City of Abbotsford260 m Enn’s Brook; 120 m suitableMunicipal parkland
City of AbbotsfordEast Fishtrap Creek Park1500 m East Fishtrap Creek; 0 suitableMunicipal parkland; Upstream of suitable habitat
Brunette RiverGreater Vancouver Regional DistrictBurnaby Lake Regional Park9000 m of mainstem and tributaries; 2450 msuitableRegional parkland
City of BurnabyDeer Lake Park2400 m of Deer Lake and Creek; 515 m suitableMunicipal parkland
City of BurnabyHume Park415 m Brunette River; 415 m occupiedMunicipal parkland
City of BurnabyEast Lake Park500 m Stoney Creek; 500 m suitableProtected as municipal parkland
City of BurnabyStoney Creek Park, City of Burnaby825 m Stoney Creek; 825 m suitableMunicipal parkland
Greater Vancouver Regional DistrictBurnaby Mountain Conservation Area1565 m Stoney Creek; 500 m suitableRegional park; Extreme headwaters

Figure 4: Occupied Habitat in the Nooksack Tributaries Includes all Reaches in Occupied Watersheds Containing a Minimum of 10 Percent Riffle by Length at Low Flow

Figure 4: Occupied habitat in the Nooksack tributaries includes all reaches in occupied watersheds containing a minimum of 10 percent riffle by length at low flow.

Only 3.27 km of the 21.4 km marked consists of riffle and could actually be occupied (adapted from National Recovery Team for Salish Sucker and Nooksack Dace, 2005). Pepin Brook = Pepin Creek.