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COSEWIC Assessment and Update Status Report on the Lake Sturgeon in Canada

Limiting Factors and Threats

Limiting factors for lake sturgeon are related to climate, hydrology, and water temperature and chemistry. Climate, and resulting hydrological conditions, may be determinants of year-class strength. Low flows and low water temperatures during spawning have been shown to have a negative influence on fecundity of Russian sturgeon(Acipenser gueldenstaedtii) in the Volga River (Khoroshko 1972), and on white sturgeon in the Sacramento, San Joaquin and Columbia rivers (Kolhorst et al. 1991). In the St. Lawrence River, year-class strength appears to be determined in the first few months of life. Climatic and hydrological conditions in June, during which larvae drift from spawning grounds and exogenous feeding begins, were identified as critical determinants of year-class strength in this river (Nilo et al. 1997). Conversely, high water temperatures may be lethal in the early embryonic development of lake sturgeon. Successful incubation seems to be possible within a temperature range of 10-18°C, but highest survival and uniform hatching appear within a narrower range of 14-16°C in white sturgeon and lake sturgeon. Temperatures of 18-20°C lead to substantial deformities and mortality and temperatures above 20°C are lethal (Wang et al. 1985).

Threats to the lake sturgeon include overexploitation, dams, habitat degradation, contaminants, and introduced species. Undoubtedly, commercial fishing was the most significant factor that caused the historical decline of lake sturgeon populations. All lake sturgeon populations that have been impacted by exploitation have declined, many to very low levels (Brousseau 1987; Houston 1987; NatureServe 2004). As this is a slow growing, late maturing, intermittently spawning species, depleted populations, even when protected, may take many years to recover, if at all. As local commercial fishing operations have ceased across the range of the species, the decline has slowed or stopped in many populations, but none have recovered to historic abundance, and some have become extirpated (NatureServe 2004). Where commercial fishing still exists, it typically is based on small quotas. For example, acommercial fishery currently exists in the Canadian waters of Lake St. Clair. Fish are caught using baited set-lines, and the annual commercial harvest ranges from 500 to 800 kg (Locke pers. comm.).

The high value of sturgeon roe and smoked meat encourages poaching, even from depleted stocks. While the impact of poaching is difficult to determine, it is estimated that several thousand lake sturgeon are illegally sold each year. It has been reported thatblack market prices for white sturgeon steaks are as high as $15-25/kg (Ptolemy and Vennesland 2003). An organized poaching ring, operating in the Pacific Northwest, provided large quantities of white sturgeon caviar to retailers, much of it marketed to the public as beluga (Huso huso) caviar (Waldman 1995). There are reported to be black markets in Alberta where lake sturgeon flesh brings similar prices and processed roe may fetch in excess of $100/kg (J. Stock, Saskatchewan Parks and Renewable Resources, Maple Creek, SK; personal communication). Dumont et al. (1987) indicated that in the 1980s illegal fisheries in the St. Lawrence River system were extensive and well organized, targeting large spawning fish.

Dams have direct and indirect effects on lake sturgeon. Dams may directly impact lake sturgeon by acting as barriers to movement at certain times of the year, especially during spawning. Unless these dams are redesigned to allow fishes to move freely, impacts on migrations will continue to be substantial (Thuemler 1985; Ferguson and Duckworth 1997). In Lac Saint François, the combined effects of the gradual construction of dams at both extremities of the lake between 1912 and 1958 and of the overfishing of the residual stock likely caused the collapse of lake sturgeon there. Since the beginning of the 1960s, sturgeon movement between the St. Lawrence River and the Ottawa River has been almost completely blocked by the Carillon hydroelectric dam at the head of Lac des Deux Montagnes, contributing to the collapse of lake sturgeon in the Ottawa River reach between Carillon and Gatineau (Dumont et al. 1987). Many other historic spawning tributaries in the St. Lawrence River may also be inaccessible due to the construction of dams and barriers.

Dams may directly impact lake sturgeon by entrainment, seasonal disruptions in habitat, and disrupting spawning triggers and timing. McKinley et al. (1998) showed that loss due to entrainment at the Little Long Generating Station in the Mattagami River system of northern Ontario is highest during the spring freshet when the plant is under continuous operation. During the operation of hydroelectric dams, flow rates change based on demand and these changes may be unpredictable. Such fluctuating flow rates are detrimental to sturgeon movements. Findlay et al. (1997) concluded that lake sturgeon populations in the South Saskatchewan and Saskatchewan rivers had experienced significant declines and stress associated with overexploitation prior to the construction of any dams. They further concluded that modification of the hydrological regime following the construction of three major dams (E.B. Campbell, Gardiner and Grand Rapids), in concert with increased water consumption for residential and agricultural purposes, resulted in major loss and degradation of sturgeon habitat, resulting in reduced recruitment in already stressed populations. The physical barriers also further fragmented the populations and reduced any chance of recruitment by immigration, as well as increasing mortality rates from wounding and death caused by entrainment in the turbines. The Moose River basin is one of the most fragmented river systems in Canada, but the impact of dams on lake sturgeon is largely unknown (Seyler 1997a).

Dams undoubtedly cause habitat fragmentation resulting in the separation/exclusion of particular life stages (adults upstream and yearling/juvenile downstream), as well as stranding downstream after peaking plant flows (McGovern, pers. comm.). Auer (1996b) found that 74% more lake sturgeon of greater weight and increased reproductive readiness spawned below the Pickett hydroelectric facility on the Sturgeon River, Michigan when flows were returned to near natural levels. Sixty-eight percent more females were found in these years and spawning sturgeon of both sexes spent less time on the spawning grounds (Auer 1996b).

Natural flow, in combination with temperature, may represent an important CPUE that stimulates spawning in lake sturgeon. While waiting for these CPUEs in areas of perturbed flow, spawning may be delayed and the energy needed for reproduction may be diverted to other body functions (Khoroshko 1972; Auer 1996b). Auer (1996b) reported that in years of unnatural, dramatically fluctuating and interrupted water flow, lake sturgeon remained in the spawning area below Pickett Dam for 4 to 6 weeks longer than during years of natural flow. In these years, little evidence of spawning was recorded and few fish were in reproductive condition although water temperatures were within the normal range for spawning (Auer 1996b). Khoroshko (1972) reported that the condition of female Russian sturgeon was negatively affected when fish were forced to expend energy during their pre-spawn period in areas of unnaturally high flow associated with hydroelectric dams. A reduction in the quality and quantity of eggs resulted (Khoroshko 1972). Lake sturgeon may be affected in a similar manner (Auer 1996b). For example, increased flows at critical spawning times could carry eggs to suboptimal habitat for food and protection from predators, and lowered water levels could expose eggs to dessication as the sticky egg surface ensures they can attach to rocky substrates immediately after fertilization. McKinley et al. (1993) reported that lower concentrations of plasma nonesterified fatty acids may be attributed to altered nutritional status due to varying flow regime located downstream of hydroelectric stations.

The construction of fishways might help alleviate the problem of habitat fragmentation, but would not remedy the loss and degradation of habitat resulting from the modification of flow regimes. However, the swimming ability of sturgeon is different than that of species for current fishway designs, and their large size further complicates design of adequate safe passages (Peake et al. 1997). Each year since 2001, only a few large lake sturgeon are among the thousands of fish, belonging to more than 35 species, which use the Vianney-Legendre fishway on the Richelieu River (Fleury and Desrochers 2004).

Habitat degradation associated with other human activities also has been identified as a threat. For example, in the past, the lower reaches of the Assiniboine River were an important area for lake sturgeon because of a rich macroinvertebrate food source [i.e. mayfly larvae (Choudhury and Dick 1993)]. Today this reach of the river suffers from deterioration in overall water quality due to erosion, suspended sediments and the addition of sewage effluents.

Contaminants often have been suggested as a cause for decline in lake sturgeon (Harkness and Dymond 1961; Mongeau et al. 1982; Rousseaux et al. 1995). In an attempt to evaluate the effects of contaminants on lake sturgeon, bioindicators were measured in a sample of lake sturgeon from two sites: Des Prairies River, confluent with the St. Lawrence River (Montréal), and a reference site in the upper reach of the Ottawa River in the La Verendrye Park. Negative effects of organics contaminants were suspected, fish taken from the Des Prairies River having moderate to severe hepatic pathology (Rousseaux et al. 1995). Among larvae raised in an artificial stream, prevalence of fin deformities was highly significantly greater in the progeny of lake sturgeon sampled in Des Prairies River (6.3%) compared with the progeny of lake sturgeon from the reference site (1.7%) [Doyon et al. 1999]. Concentrations of liver and intestine retinoids were also found to be significantly lower (as much as 40 times lower) in the Des Prairies River sample (Doyon et al. 1998, 1999; Ndayibagira et al. 1995).

Wood fibre and chemical effluent from pulp and paper mills, along with agricultural runoff and siltation, have been found to degrade known lake sturgeon spawning areas (Mosindy 1987). An accidental discharge of toxic effluent caused a large die-off of lake sturgeon along the St. Lawrence River in 1984 (Dumont et al. 1987). Levels of mercury and polychlorinated biphenyls (PCBs) in lake sturgeon have been much higher than acceptable (Hart 1987) and the Lake St. Clair lake sturgeon fishery was closed in 1970 due to mercury contamination (Baldwin et al. 1978), but re-opened in 1991. As the lake sturgeon is a benthic species, fish often are exposed to high contaminant loads. Individuals exposed to systems with high contaminant loads compared to non-contaminated systems had lower retinoids than fish in non-contaminated systems (Ndayibagira et al. 1995).

Contamination of habitat resulting from agricultural practices has had an adverse impact on many populations, especially in the Prairies (Graham 1981; Pflieger 1975; Mosindy 1987; NatureServe 2004). Farmers use 35 times as much fertilizer as they did a half-century ago with phosphorus and nitrogen, in particular, significantly adding to the nutrient loading of many lakes and streams. Domestic livestock production also poses problems where manure and waste products can enter the water from feedlots located near streams, manure spread on fields or over ice in winter (DFO 1992). Channelization, ditching, tilling and land clearing also have led to increased sedimentation and loss of cover; thereby leading to habitat loss and degradation in the tributaries to Lake Erie and throughout much of the mid-west in the United States (NatureServe 2004), the Prairies (DFO 1992) and the Rainy River in northern Ontario (Mosindy 1987).

Sediment disposal operations can affect sturgeon directly by causing direct mortality of different life history stages by burial and gill clogging, or indirectly by habitat degradation (Hatin et al. in press). Dredging and dumping operations conducted for the construction of the navigation channel and the St. Lawrence Seaway in the 1950s and 1960s caused major manmade habitat changes. Channel and harbour maintenance is now an annual occurrence (Dumont et al. 1987, Robitaille et al. 1988) and there is a need to learn more about the relationship between habitat characteristics, feeding and distribution of lake sturgeon in the river (Nilo et al. 2006). In a large-scale study on sediment disposal in the Upper Estuary, Hatin et al. (in press) observed site avoidance and a negative impact of sediment disposal operations for Atlantic sturgeon but not for lake sturgeon, likely because the lake sturgeon diet is more diversified.

Lake sturgeon from swim-up size to about 120 mm have been shown to be very sensitive to the lampricide TFM used to control sea lamprey (Petromyzon marinus) in the Great Lakes basin (Johnson et al. 1999, Boogaard et al. 2003). As a result of the high degree of overlap between the historic distribution of lake sturgeon and sea lamprey distribution in the Great Lakes basin, TFM may pose a significant threat to lake sturgeon (Auer 1999). Sea lamprey control programs in the Great Lakes basin have developed treatment protocols to minimize impacts on lake sturgeon (Holey et al. 2000); however, these protocols are now being relaxed as sea lamprey numbers are increasing.

Other threats may include the introduction of non-native species such as zebra mussel (Dreissena polymorpha), rainbow smelt (Osmerus mordax), and round goby (Neogobius melanostomus), that may compete for food and habitat, prey on eggs and fish, and cause habitat disturbances (DFO 1992, Scott and Crossman 1998). The introduction of non-native plants, such as Eurasian water milfoil (Myriophyllum spicatum) and purple loosestrife (Lithrum salicaria), also could lead to habitat disruption and reduction in diversity (DFO 1992).