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Recovery Strategy for the Salish Sucker (Catostomus sp.) in Canada (proposed)

1. Background

1.1 Species information

The status report and assessment summary for Salish Sucker is available from the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) Secretariat.

Common name: Salish Sucker

Scientific name: Catostomus sp.

Assessment Summary: November 2002

COSEWIC Status: Endangered, April 1987 and May 2000

Species at Risk Act (SARA) Status: Endangered, June 2005

Reason for Designation: This species has a restricted range in Canada, and is in significant decline due to habitat loss and degradation.

Range in Canada: British Columbia

Status History: Designated Endangered in April 1996. Status re-examined and confirmed in May 2000. Last assessment based on an existing status report

1.2 Species description

The Salish Sucker (Catostomus sp.) is closely related to the Longnose sucker (C. catostomus), a widespread species in North America. The two taxa diverged when a population became geographically isolated in the Chehalis River valley (present-day Washington State) sometime during the Pleistocene glaciations (McPhail 1987). The Salish Sucker is considered an evolutionarily significant unit (McPhail & Taylor 1999) and can be considered a “species in the making” (McPhail 1987), although its precise taxonomic status is currently being investigated.

The Salish Sucker is dark-green, mottled with black dorsally, dirty-white ventrally and develops a broad red lateral stripe during the spawning season. This stripe is especially vivid in males. Scales are fine, the snout is short and blunt, and the small mouth is located on the lower surface of the head (McPhail & Carveth 1994). Few males exceed 200 mm (fork length) and they can reach sexual maturity at less than 100 mm; females seldom exceed 250 mm (Pearson & Healey 2003).

1.3 Populations and distribution

Populations of Salish Suckers have been documented in 11 British Columbia watersheds, all in the Fraser Valley. At least four others occur in northwestern Washington State (Figure 1). The population in Little Campbell River, BC is believed to have been extirpated, although there is an unconfirmed report of Salish Suckers in a pond within the floodplain of the Little Campbell (Pearson pers. comm. 2011). Current information suggests that approximately 25% of the global range and 70% of all populations are in Canada (Figure 1). The species has been in decline since at least the 1960s (McPhail 1987), and probably for much longer (Pearson 2004a).

Figure 1. Distribution of the Salish Sucker

Maps showing the distribution of Salish Sucker in Canada (see long description below).

In Canada (left panel), the Salish Sucker has been observed in eleven watersheds: (1) Little Campbell River, (2) Salmon River, (3) Bertrand Creek, (4) Pepin Brook, (5) Fishtrap Creek, (6) Salwein Creek/Hopedale Slough, (7) Chilliwack Delta (Atchelitz/Chilliwack/ Semmihault Creeks), (8) Elk Creek/Hope Slough, (9) Mountain Slough, (10) Agassiz Slough, (11) Miami Creek. Globally, it is also found in four other watersheds in northwestern Washington (right panel).

Description of Figure 1

Figure 1 is a map showing the distribution of Salish Sucker in Canada. The map depicts the Fraser Valley and Lower Mainland area of British Columbia, stretching from Vancouver on the west side of the map to Harrison Lake in the northeast corner of the map to the United States border along the southern border of the map. The following watersheds where Salish Sucker have been observed are identified on the map: Salmon River, Bertrand Creek, Pepin Brook, Fishtrap Creek, (Salwein Creek/Hopedale Slough, Chilliwack Delta (Atchelitz/Chilliwack/ Semmihault Creeks), Elk Creek/Hope Slough, Mountain Slough, Agassiz Slough, and Miami Creek. The Little Campbell River watershed is depicted as a watershed where the Salish Sucker is believed to be extirpated. A second map shows the global distribution of Salish Sucker in southwestern British Columbia and western Washington State. In addition to the watersheds listed above, four watersheds in Washington State where Salish Sucker is known are identified (adapted from Pearson 2004a and McPhail 1997).

In the current landscape, there are virtually no aquatic connections between adjacent populations. Exceptions include a small headwater pond that feeds both Mountain Slough and Miami Creek and an occasional high water connection between Bertrand Creek and the Salmon River via a headwater wetland (Pearson pers. comm. 2010). The only other route between watersheds is via the mainstem Fraser River or Nooksack River, although no Salish Suckers have ever been reported from either and captures in larger sloughs are extremely rare (Pearson pers. comm. 2010). Prior to the drainage of Sumas Lake (1920s) and the construction of the dyke system following the 1948 flood, permanent and high water connections among populations would have been more common. This raises the possibility that the populations were historically linked in a meta-population structure.

1.4 Description of the species' needs

1.4.1 Biological needs, ecological role, and limiting factors

Salish Suckers are well-equipped to inhabit headwater streams, where habitat conditions may vary widely on daily, seasonal, and longer time scales. They tolerate higher temperatures and lower dissolved oxygen levels than most other native fish that occur in this region of British Columbia. The major natural limiting factor for populations is the availability of high quality habitat. Salish Suckers have life history characteristics that promote rapid population growth, given adequate habitat. Compared to Longnose sucker, the Salish Sucker is small, short-lived, and early-maturing. Most spawn for the first time in their second year, and they rarely live beyond 5 years (McPhail 1987). Salish Suckers begin spawning in April, but the period is protracted (6 to 8 weeks, Pearson 2004a), relative to the Longnose sucker (2 to 3 weeks, Barton 1980; Schlosser 1990; Scott & Crossman 1973), a trait that increases fecundity in species otherwise limited by small female body size (Blueweiss et al. 1978; Burt et al. 1988). Spawning occurs between early April and mid July (McPhail 1987; Pearson & Healey 2003) and egg incubation is likely complete by mid-August.

1.4.2 Habitat needs

Physical habitat

Adults are most abundant in marshes and American beaver (Castor canadensis) ponds with mud or silt substrates. The proportion of channel deeper than 70 cm is the strongest predictor of adult presence in a reach. Occupied reaches also have significantly less riffle and more in-stream vegetation than reaches in which Salish Suckers are absent. Although fewer data exist for young-of-the-year, they appear to be associated with shallow pool and glide habitats containing abundant vegetation (Pearson 2004a). Spawning typically occurs in gravel riffles (McPhail 1987), but groundwater upwellings are likely used in systems lacking riffle habitats (Pearson unpublished data). Most individuals appear to have small home ranges (mean of 170 m of channel) although some individuals are known to venture thousands of metres during the spawning period (Pearson & Healey 2003).

Water quality

Water must have oxygen, pH, temperature, and toxin levels that are not harmful to the species. Salish Suckers appear well-adapted to low oxygen environments and have been captured in areas with concentrations below 2 mg/L (Pearson unpublished data). Sublethal effects (e.g., reduced growth and fecundity) likely occur at these concentrations. Based on observation and experience, an appropriate target for dissolved oxygen in Salish Sucker habitat is ≥ 4 mg/L. This is lower than the federal water quality guideline for aquatic life (5 mg/L, CCREM 1987), but these are intended to protect species like salmonids, which are very intolerant of hypoxia. Thermal tolerances of the Salish Sucker are unknown, but activity is minimal at temperatures below 6°C (Pearson & Healey 2003) and apparently healthy fish have been caught in temperatures of up to 23°C (Pearson unpublished data). The sensitivity of Salish Suckers to toxic contamination is unknown. Salish Suckers are generally absent from reaches where the landscape within a 200 m radius of the channel is more than 50% urban by area (Pearson 2004a). These reaches invariably receive urban stormwater containing contaminated sediments from road runoff (Hall et al. 1991). As bottom-dwelling fish, Salish Suckers in these habitats are likely to be chronically exposed to toxins in sediments.

Spatial distribution and temporal stability of habitats

Distribution of the Salish Sucker is clumped, with a few sites harbouring most individuals (Pearson 2004a). These ‘hotspots’ likely result from rare convergences of optimal levels in a few key environmental variables (Brown et al. 1995). For Salish Suckers these variables likely include extensive areas of deep water (100s of metres of channel) close to spawning riffles and shallow nursery habitat, adequate water quality, and low predation pressure (Pearson 2004a). Most individuals appear to confine their movements to a single reach but some individuals travel more widely (Pearson & Healey 2003). Clumped distribution and bimodal movement patterns suggest that metapopulation and/or source-sink population dynamics characterize the species. If so, factors affecting migration between sub-populations (the proximity of ‘hotspots’ to one another and the occurrence of movement barriers between them) are likely important to long-term population viability. Natural disturbance and succession may produce a pattern in which the location of hotspots moves throughout the landscape over time, but are occasionally eliminated by catastrophic events (Ives & Klopper 1997). Such catastrophic declines at the reach scale have been documented for the Salish Sucker (Pearson 2004a), but the effect on extinction risk for Salish Sucker populations is unknown.