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

2. Threats


2.1 Identification of threats to the survival of the species

The potential for recovery of a species at risk depends on the magnitude, timing, frequency, duration and extent of threats it faces. The following sections summarize detailed analyses published elsewhere (Pearson 2004a, b).

Eight factors (Table 1) were considered threats based on knowledge of species biology and habitat conditions across the Canadian range. All are proximate, in that they act directly on Salish Suckers or their habitats. Factors known to drive or trigger threats are described in Figure 2. The vulnerability of the Salish Sucker to each threat and the severity of each threat in each watershed are rated and summarized in Table 2. The ratings are based on analyses of a suite of indicators that cause, exacerbate or mitigate threats. A summary by watershed is presented in Table 3. For details of assessment methods and rationale for ratings see Pearson (2004a; 2004b).

Table 1. Potential threats to the Salish Sucker in Canada.
ThreatManagement Concern
1) HypoxiaEpisodes of extreme hypoxia cause acute mortality or reduced fitness.
2) Physical Destruction of HabitatDrainage, dyking, channelization and infilling of waterbodies destroys habitat.
3) Habitat FragmentationPermanent or temporary barriers such as perched culverts, beaver dams, and agricultural weirs prevent or inhibit fish from traversing some stream reaches. This restricts access to usable habitats and/or alters metapopulation dynamics, and increases extinction risk.
4) ToxicityToxic discharges from point and non-point sources reduce survival or fitness.
5) Sediment DepositionDeposited sediment degrades habitat by reducing invertebrate (food) density, reducing the flow of oxygenated water to eggs in riffles and, in severe cases, by infilling pools.
6) Seasonal Lack of WaterLow flows in late summer eliminate habitat, reducing fitness or survival.
7) Increased PredationIntroduced predators consume individuals or reduce their fitness by inducing behavioural changes (e.g. increased energy expenditure and reduced energy intake)
8) Riffle Loss to Beaver PondsBeaver ponds flood riffle habitat.

 

Table 2. A threats assessment summary for the Salish Sucker. See text for more details.
ThreatVulnerabilitySeverity Across Range
Hypoxiamajor concernmajor concern
Physical Destruction of Habitatmajor concernmajor concern
Habitat Fragmentationmoderate concernmajor concern
Toxicitymoderate concernmoderate concern
Sediment Depositionmoderate concernmoderate concern
Seasonal Lack of Waterminor concernmoderate concern
Increased Predationminor concernmoderate concern
Riffle Loss to Beaver Pondsminor concernminor concern


Figure 2. Factors known or suspected to drive or trigger threats to the Salish Sucker

Flow chart (see long description below).

Description of Figure 2

Figure 2 describes the interaction of factors known or suspected to drive or trigger threats to the Salish Sucker (from Pearson 2004a). Contributing factors including nutrient loading, dredging, dyking, channelization, draining, infilling, water withdrawal, impermeable soils, impermeable surfaces, lack of riparian vegetation, poor erosion control, beaver ponding, pesticide / herbicide use, toxic spills and introduced species are shown as contributing to threats to the species which then affect the abundance and distribution of Salish Sucker and Nooksack Dace.

 

Table 3. Assessment of threat severity in each of the watersheds in Canada where Salish Suckers have been observed. Background data and details of assessment methods are provided by Pearson (2004a). The assessment of Elk/Hope Slough is based on data collected very recently (Pearson unpublished data).
ThreatBertrand CreekPepin BrookFishtrap CreekUpper Salmon RiverSalwein/ Hopedale SloughAtchelitz/
Chilliwack/
Semmihault
Miami CreekMountain SloughAgassiz SloughElk / Hope SloughLittle Campbell River
Hypoxiamoderate concernmajor concernmoderate concernmajor concernmajor concernmoderate concernmajor concernmajor concernmajor concernmoderate concernmajor concern
Physical Destruction of Habitatmoderate concernmajor concernmajor concernmoderate concernmajor concernmajor concernmoderate concernmajor concernmajor concernmajor concernmoderate concern
Habitat Fragmentationmajor concernmoderate concernmoderate concernmoderate concernmajor concernmajor concernmoderate concernmoderate concernmajor concernmoderate concernmoderate concern
Toxicitymoderate concernminor concernmajor concernminor concernmoderate concernmoderate concernmoderate concernmoderate concernmajor concernmoderate concernmoderate concern
Sediment Depositionmoderate concernmajor concernmoderate concernmoderate concernminor concernmoderate concernmoderate concernmajor concernmoderate concernmajor concernmoderate concern
Seasonal Lack of watermajor concernminor concernmoderate concernmajor concernminor concernminor concernmoderate concernmoderate concernmajor concernminor concernmoderate concern
Increased Predationmoderate concernmoderate concernmoderate concernminor concernmoderate concernmoderate concernminor concernminor concernminor concernmoderate concernmajor concern
Riffle Loss to Beaver Pondsminor concernmajor concernminor concernminor concernminor concernminor concernminor concernminor concernminor concernminor concernmoderate concern

 

2.1.1 Threat 1: Hypoxia

Description

There are several interacting causes of hypoxia, but it is ultimately caused by the cumulative effects of local and watershed-scale impacts. Nutrients in Fraser Valley groundwater and streams are elevated, primarily as a consequence of over-application of manure and fertilizers to agriculture lands (Lavkulich et al. 1999; Schreier et al. 2003), but also from urban stormwater runoff and septic systems (Lavkulich et al. 1999). Increased nutrients result in algal blooms and high densities of macrophytes that strip the water of oxygen at night. Decomposition of dead algae and vegetation exacerbates the problem and may severely depress daytime oxygen levels as well. Lack of shade from riparian vegetation promotes increased water temperatures. Warmer water has less capacity for dissolved oxygen (DO) and increases the metabolic demands of fish and other organisms. Reduced water movement impairs reoxygenation of water and may be caused by channelization, (Schreier et al. 2003), beaver ponds (Fox & Keast 1990; Schlosser & Kallemyn 2000), or low flows.

Vulnerability (major concern)

Salish Suckers are able to tolerate moderate hypoxia and have been captured in areas with concentrations below 2 mg/L (Pearson, unpublished data), yet occasional reach-scale kills of Salish Suckers due to severe hypoxia likely occur. A marsh in Pepin Brook that contained a very high density of Salish Suckers between 1999 and 2002 (over 1000 fish in 1420 m2 of habitat) was near anoxic (DO <1.5 mg/L) and apparently devoid of fish in 2003 (Pearson 2004a). Levels at which sub-lethal effects (e.g., reduced growth, fecundity) occur are unknown. Eggs, larvae, and over-wintering fish are unlikely to be affected by severe hypoxia as it usually occurs in mid to late summer when flows are low and temperatures are high. A DO concentration of ≥ 4 mg/L is likely adequate for the Salish Sucker (see 1.4 Description of the Species’ Needs).

Severity (major concern)

Along with direct habitat destruction, hypoxia appears to be the most serious threat to Salish Sucker populations range-wide. It is a major concern in seven of the 11 watersheds (Table 3). When 58 km of stream areas identified as critical habitat in this recovery strategy were surveyed during late summer 2004, the DO concentration was less than 4 mg/L in 40% of the habitat and less than 2 mg/L in 21% of the habitat (Pearson unpublished data). DO measurements were made during the day, but since the lowest dissolved oxygen levels occur at dawn these are conservative numbers. One of the main factors contributing to hypoxia, nutrient loading, has increased greatly with agricultural intensification in the Fraser Valley (Hall & Schreier 1996). Manure application on agricultural lands in Abbotsford is currently adding approximately three times the amount of nitrate that crops can take up, and the ratio is increasing (Schreier pers. comm. 2005); the excess enters groundwater and surface waters.


2.1.2 Threat 2: Physical destruction of habitat

Description

Channelization, dredging and infilling directly destroy or degrade stream habitats. Channelization reduces channel length (and habitat area), and exacerbates hypoxia by reducing mixing. Dredging removes spawning riffles and other habitat features, and infilling destroys all affected habitats.

Vulnerability (major concern)

Like all species, Salish Suckers are highly vulnerable to large-scale destruction of their habitat. The highest densities of Salish Suckers are found in marshes and beaver ponds (Pearson 2004a), habitats that have often been drained and turned into agricultural lands.

Severity (major concern)

Approximately 77% of pre-settlement wetland areas in the Fraser Valley have been drained or infilled (Boyle et al. 1997). Fifteen percent of the area’s streams no longer exist, having been paved over or piped (Fisheries and Oceans Canada 1998). A large, but unknown, proportion of those that remain have been channelized and/or repeatedly dredged for agricultural or urban development. It is difficult to overstate the historical extent of fish habitat loss from these activities. Both permitted and illegal dredging of ditches and stream channels for flood control and agricultural drainage still occur annually in all watersheds known to have Salish Suckers. Along with hypoxia, physical habitat destruction ranks as the most severe threat facing the species. It is considered a major concern in seven of the 11 watersheds and a moderate concern in the remaining four (Table 3). The loss of historic habitats means Salish Suckers are now more dependent on those habitats remaining.


2.1.3 Threat 3: Habitat fragmentation

Description

Physical barriers such as perched culverts, beaver dams, and agricultural weirs commonly prevent fish movement between habitats for all or part of the year in Fraser Valley streams. In addition, any of the other threats discussed may fragment habitat by preventing or curtailing movement of fish within and among affected reaches. On a larger scale, connections between watersheds during floods were undoubtedly more common prior to the extensive dyking and drainage works of the past century.

Vulnerability (moderate concern)

Distribution of the Salish Sucker is clumped, and a small proportion of habitat contains the majority of individuals (Pearson 2004a). Individuals usually stay within a small home range (less than 200m of channel), but occasionally travel longer distances, especially during the spawning period (Pearson & Healey 2003). This suggests that each watershed is inhabited by core subpopulations connected by occasional migration. Movement between these subpopulations typically requires traversing several kilometres of stream, or crossing watershed boundaries during occasional high-water connections. Most barriers and habitat fragmentation in Salish Sucker watersheds date from the past 50 to 130 years, and surviving populations have shown some resilience (Pearson 2004a). The effects, however, may occur over longer time frames. The effect of fragmentation on the long-term persistence of the Salish Sucker is unclear, though where access is available, Salish Sucker populations have demonstrated an ability to colonize new habitat quickly (Patton 2003).

Severity (major concern)

The destruction of aquatic habitat that has occurred within the Fraser Valley over the past 150 years has fragmented available habitat. At the regional scale, high-water connections between watersheds still occur annually in some systems (Miami Creek with Mountain Slough) and at least every few years in others (Bertrand Creek with the Salmon and Little Campbell Rivers, Pearson 2004a), but many former connections have been lost or weakened. The drainage of Sumas Lake, the diversion of the Chilliwack River away from its delta, and the isolation of Agassiz Slough by a dyke and highway overpass are the starkest examples (Pearson 2004a). Within watersheds, physical barriers such as perched culverts, beaver dams, and agricultural weirs commonly prevent movement between some habitats for all or part of the year in virtually all Fraser Valley streams. Historic habitat losses mean greater dependence of the Salish Sucker on those habitats that remain.


2.1.4 Threat 4: Toxicity

Description

Toxic compounds enter Fraser Valley streams through urban storm runoff, contaminated groundwater (e.g., agricultural pesticides and herbicides), direct industrial discharges, sewage treatment plant effluents, aerial deposition, and accidental spills (Hall et al. 1991). Concentrations in the water column are variable over time because dilution varies with stream discharge and inputs are often pulsed (e.g., first flush of stormwater following a long dry spell, Hall et al. 1991). Some contaminants, particularly heavy metals, bind to sediments where they may be taken up and bioaccumulated by aquatic invertebrates and subsequently fish.

Vulnerability (moderate concern)

Data on threshold concentrations for acute and sublethal effects to the Salish Sucker are lacking. The Salish Sucker may be sensitive to contaminants in food items and the water column, and as a bottom-dwelling species that feeds primarily on benthos it may be sensitive to contaminants bound to sediment. Salish Suckers are less likely to be found in reaches where land use within 200 m of the channel is predominantly urban (Pearson 2004a). This may be partly due to toxic materials originating from storm sewer outfalls.

Severity (moderate concern)

Toxicity is considered a moderate threat range-wide. It is poorly documented in most Salish Sucker streams, but is likely present to some degree in all. It is a major concern in localized areas. Agassiz Slough sediments, for example, are contaminated by urban storm runoff and contain copper and zinc levels in excess of recommendations for protection of aquatic life (Schreier et al. 2003). Portions of three other streams (Bertrand Creek, Fishtrap Creek, and Atchelitz/Chilliwack/Semmihault) also receive stormwater from adjacent urban areas and are likely also contaminated. Pesticides and herbicides have been detected in both surface water and groundwater in Salish Sucker watersheds (Hall et al. 1991; Schreier et al. 2003). The list of compounds that could enter creeks from spraying, poor waste management, and accidental spills is enormous.


2.1.5 Threat 5: Sediment deposition

Description

Sediment deposition is controlled by the balance between the rate of sediment delivery to the channel and capacity of the stream to mobilize and carry it downstream. Sediment delivery may be increased by direct discharges, storm drain runoff, or bank erosion accelerated by lack of riparian vegetation and/or increased peak flows (Waters 1995). All of these sources are likely to increase with urban, agriculture and mining development in a watershed.

Vulnerability (moderate concern)

Salish Suckers spawn in riffles between April and early July (Pearson & Healey, 2003) and are probably most susceptible to sedimentation in these habitats during this period. Salish Suckers are less likely to be found in reaches where land use within 200 m of the channel is predominantly urban (Pearson, 2004a); sediment inputs from storm sewer outfalls and its deposition on riffles may partially explain this.

Severity (moderate concern)

Sediment deposition and its negative effects on reproduction are moderate concerns in almost all Salish Sucker watersheds (Table 3). Chronic, large-scale releases from gravel pits have filled in pools and largely eliminated instream cover and food sources from a critical habitat reach in Pepin Brook.


2.1.6 Threat 6: Seasonal lack of water

Description

During late summer, when rainfall is sparse, Fraser Valley stream flows are maintained almost solely by groundwater. Stream hydrographs vary widely depending on surface soil permeability and water use. Watersheds with large unconfined aquifers or mountain tributaries fed by snow melt (e.g., Elk Creek) maintain steady flows of cold water throughout this critical period, while surface flows may cease completely in watersheds with impermeable surface soils (e.g., Bertrand Creek and tributaries). Unfortunately, the late summer low-flow period coincides with peak demand for water from wells and streams for irrigation and domestic use, which can lower water levels further. Common land use changes in the Fraser Valley also tend to exacerbate problems with lack of water. Gravel mining reduces the size of the aquifer contributing to base flow, urban development increases the area of impermeable surfaces, reducing infiltration to the aquifer, and drainage for agriculture lowers water tables, further reducing low flows. Beaver ponds are a stabilizing force, maintaining water levels in reaches that may otherwise dry out. Beaver dams can improve low flows by augmenting groundwater levels and via seepage through the dams (Stabler 1985, Gurnell 1998).

Vulnerability (minor concern)

The deep pool habitats preferred by Salish Suckers rarely dry out completely. Spawning and egg incubation occur in spring and early summer, when water is generally plentiful. Lack of water is a potentially exacerbating factor for several other threats including hypoxia, toxicity, habitat fragmentation and introduced predators.

Severity (moderate concern)

Lack of water is a moderate concern range-wide. It is a major concern in three of the eleven watersheds, a minor concern in three and a moderate concern in the remaining five (Table 3).


2.1.7 Threat 7: Increased predation

Description

Increased predation is most likely to arise from the introduction of new predators to Salish Sucker habitats. Such introductions are implicated in the extinction of numerous native fishes across North America (Miller et al. 1989; Richter 1997; Gido & Brown 1999).

Vulnerability (minor concern)

The impacts of introduced predators on Salish Sucker populations are unknown, but do not appear to be severe. Salish Suckers have coexisted with Brown bullheads, Ameiurus nebulosis, bullfrogs, Rana catesbeiana, and/or Largemouth bass, Micropterus salmoides, for at least ten years in various parts of the range (Pearson, unpublished data). All three likely prey on juvenile Salish Suckers, and Largemouth bass become large enough to consume adults. Their impacts probably vary with habitat attributes. All three of these predators thrive in warm water littoral zones. The Brown bullhead is also extremely tolerant of hypoxia (Scott & Crossman 1973). Other introduced fish species, such as Smallmouth bass Micropterus dolomieu, Black crappie Pomoxis nigromaculatus and Pumpkinseed sunfish Lepomis gibbosus are spreading in the region, through unauthorized introductions and subsequent range expansions (Hatfield & Pollard 2006). Introduced Smallmouth bass are implicated in the extirpation of small-bodied fish species from lakes in eastern Canada (Chapleau et al. 1997; Whittier et al. 1997; Vander Zanden et al. 1999; Whittier and Kincaid 1999; Findlay et al. 2000; MacRae and Jackson 2001). Introduced species may alter habitat use by Salish Suckers and exacerbate other habitat effects such as increased water temperatures or the frequency and severity of hypoxia. Alternatively, recovery efforts to increase habitat complexity may reduce impacts from introduced species by providing areas of refuge (Jackson et al. 2001).

Severity (moderate concern)

Introduced predators inhabit every stream known to contain Salish Suckers. The threat of effective, new predators being introduced is also ever present.


2.1.8 Threat 8: Riffle loss to beaver ponds

Description

Beaver ponds have been shown to influence fish populations both positively and negatively (Hanson & Campbell 1963; Keast & Fox 1990; Lavkulich et al. 1999; Schlosser 1995), but the impacts of riffle loss through ponding has received scant attention.

Vulnerability (minor concern)

As long as the relatively small amount of riffle habitat necessary for spawning remains intact, riffle loss to beaver ponds is unlikely to impact Salish Sucker populations, although other aspects of ponding are (Pearson 2004a). By stabilizing the otherwise highly variable environments of headwater streams (Hanson & Campbell 1963; Naiman et al. 1986), beaver pond creation is likely to benefit Salish Suckers. Indeed, during late summer low-flow periods, beaver ponds provide the only wetted habitat in a number of reaches (Pearson 2004a). Dams, however, also reduce water movement, increase hypoxia and act as barriers to escape from poor conditions.

Severity (minor concern)

Riffle loss to beaver ponds is a major concern in one watershed, a moderate concern in one other, and a minor concern in the rest (Table 3).

2.2 Summary of threats analysis

Salish Sucker populations appear to be most vulnerable to severe hypoxia and habitat loss. Hypoxia is widespread, degrades areas of otherwise suitable habitat, can kill large numbers of fish quickly, has numerous contributing factors, can easily go undetected, and is likely occurring with increasing frequency. Direct habitat destruction is likely the primary cause of historical decline in Salish Sucker populations. Large portions of all creeks surveyed have been channelized, in-filled, or repeatedly dredged. Damage continues to occur through municipal ditch-cleaning activities and unauthorized works on private land.

Habitat fragmentation is considered a moderate threat to the Salish Sucker, but is also poorly understood. Toxicity, sediment deposition and seasonal lack of water appear to be major threats in particular watersheds, but do not threaten the species across the range.

Introduced predators are considered a moderate threat. Although they are numerous, occur across the Canadian range, and are commonly implicated in decline and extinction of other native species, there are several documented instances of co-existence with the Salish Sucker for more than two generations. The threat of introduction of more effective, novel predators is, however, a concern. Riffle loss to beavers may limit spawning when riffles are rare but is considered a minor concern range-wide, although the potential role of recruitment limitation in limiting Salish Sucker populations remains unknown. Beaver ponding may have opposing influences on the Salish Sucker and another Species at Risk Act (SARA)-listed fish, the Nooksack Dace, in Pepin Brook. Riffle habitats critical to Nooksack Dace are destroyed by beaver dams, but the deep, marshy habitats favoured by adult Salish Suckers are created.