Kerr, S. J., M. J. Davison and E. Funnell. 2010. A review of lake sturgeon habitat requirements and strategies to protect and enhance sturgeon habitat. Fisheries Policy Section, Biodiversity Branch. Ontario Ministry of Natural Resources. Peterborough, Ontario. 58 p. + appendices.
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The decline in lake sturgeon across much of North America has been attributed initially to unregulated fisheries and, more recently, to habitat alteration and destruction notably by pollution, dredging and channelization, and the construction of dams and hydroelectric facilities. Dredging and channelization can alter lake sturgeon spawning grounds. Sturgeon have been impacted by many forms of pollution which can disrupt olfactory feeding behaviour. Dams and hydroelectric stations can have a negative impact on lake sturgeon by fragmenting their habitat, impeding migrations to spawning grounds and, depending on the type of operation, having a negative impact on egg survival and recruitment. Downstream migrants may also be impinged or entrained at hydroelectric plants.
Attempts to resolve some of these habitat impacts have included construction of fish passes at dams, establishing base flows or “run-or-river” regimes at hydroelectric facilities, creation or enhancement of spawning areas, use of downstream guidance and diversion structures, and improvements to water quality. There has been some success with constructing artificial spawning grounds for lake sturgeon. Sturgeon have also been shown to display a positive response to improvements in water quality and “run-of-river” hydrologic regimes at dams and power stations. The ability to design a fish pass suitable for fish with the body size/shape and swimming capabilities of lake sturgeon has proven difficult, however, and further research is required in this area. Many sturgeon populations are also impacted by “peaking” operations at hydroelectric facilities and the issue of facilitating downstream passage over artificial barriers also needs to be resolved.
1. Dams and Hydro-electric Facilities
The impacts of dams, hydroelectric facilities, and other anthropogenic activities pose significant threats to lake sturgeon in Ontario. A recovery strategy for lake sturgeon in Ontario is currently being developed to provide science-based recommendations on the protection and recovery of this species. Following completion of the recovery strategy under the Endangered Species Act (2007), a government response statement will be developed summarizing the Government of Ontario’s intended actions and priorities in response to the recovery strategy.
Dams alter the normal pattern of water temperature, flow regime, water chemistry, nutrient transport, fish movement, and community structure in a river system which can affect spawning and recruitment of sturgeon (MacDonell 1995, Bednarek 2001, Threader et al. 2005, Haxton and Findlay 2009, Mora et al. 2009). It has been estimated that 77% of the northern hemisphere’s largest rivers are regulated by dams and hydroelectric facilities (Dynesius and Nilsson 1994). Altered hydrologic regimes associated with impoundment operations has been identified as a leading threat to imperilled fish fauna (Richter et al. 1996, World Wildlife Fund 2009). The construction of dams has often preceeded the decline in local sturgeon populations (Granado-Lorencia 1991, Jager 2006a). Dam construction at both extremeties of Lake St. Francis between 1912 and 1958 was attributed as one of the major causes for the collapse of local lake sturgeon stocks (Dick et al. 2006). Similarly, the construction of the Carillon hydroelectric dam on the Ottawa River has contributed to the decline in lake sturgeon in the lower portion of the Ottawa River (Dick et al. 2006). Jager et al. (2001) believed that the amount of free-flowing unobstructed river available often determined its ability to support sturgeon. Haxton and Findlay (2008) concluded that water power management was the primary factor preventing recovery of lake sturgeon in the Ottawa River.
Obstructions, such as dams, which prevent access to spawning grounds are known to have severe impacts on several sturgeon species (Ferguson and Duckworth 1997, Cooke et al. 2004, Dadswell 2006) (Appendix 2). The construction of hydroelectric dams in the Saskatchewan River watershed fragmented one single population into several subpopulations (McLeod et al. 1999). Similary, the lake sturgeon population in the Menominee River, Wisconsin, has been fragmented by hydroelectric dams (Thuemeler 1997). In the Moose River basin, Ontario, it has been estimated that the natural range of lake sturgeon has been reduced by at least 30% as a result of dam construction (MNR 2008).
In addition to blocking upstream access, dams can have other impacts on sturgeon. When blocked by the Pinopolis Dam on the Cooper River, South Carolina, shortnose sturgeon (Acipenser brevirostrum) remained below the dam for up to 89 days and eventually spawned under poor conditions. As a result, larval survival rates were extremely low (Cooke et al. 2004). Water level manipulation and pollution have also contributed to lake sturgeon declines in Alberta (Earle 2002).
Hydroelectric facilities can have serious impacts on resident fish populations (Cada and Sale 1993, Stokes et al. 1999, Steele and Smokorowski 2000, AECOM Canada Ltd. 2009). Regulated flows can disrupt normal movements and spawning patterns (Veshchev and Novikova 1984, Raspopov et al. 1994). The effects of regulated flow alters the abundance, composition, and diversity of benthic macroinvertebrates which may ultimately affect the diet and nutritional status of lake sturgeon (Fisher and LaVoy 1972, Troelstrup and Hergenrader 1990, Weisberg and Burton 1993, McKinley et al. 1993, Snyder and Minshall 2005). Aquatic habitat upstream of a dam or hydroelectric facility may be degraded or lost. For example, historic lake sturgeon spawning sites were inundated or altered with the construction of the Moses-Saunders dam on the St. Lawrence River (Edwards et al. 1989). Similarly, the construction of the Carillon dam on the lower Ottawa River flooded a historic lake sturgeon spawning site further upstream near Hawkesbury (Haxton and Findley 2008).
Shifts in the timing of naturally occurring peak flows and reductions in these flows below hydroelectric facilities are directly related to sturgeon spawning success and year class strength (Koroshko 1972, Zakharyan 1972, Votinov and Kasyanov 1979, Veshchev 1991). A dewatering event below the Peshtigo River dam, Wisconsin, after sturgeon spawning reduced the size of the 2006 year class of lake sturgeon (Caroffino et al. 2009). Haxton (2007) reported that lake sturgeon abundance was significantly greater in unimpounded reaches of the Ottawa River. A similar observation was made for white sturgeon (A. transmontanus) in the Columbia River, Oregon and Washington (Beamesderfer et al. 1995). Population declines of several sturgeon species have coincided with flow regulation associated with hydroelectric development (Khoroshka 1967, Granado-Lorencia 1991, Zhong and Power 1996).
Generally, there are two basic operating regimes at hydroelectric facilities: “peaking” and “run-of-river”. A “peaking” operation is one in which water is stored in the reservoir for a period of time and then spilled through the turbines to produce electricity. Typically, water is stored in the reservoir and released through turbines to generate electricity during the day or season when demand for electricity is highest. This results in a dramatic reduction in downstream flows for a period of many hours which has often been attributed to lowered biological diversity downstream of these sites (Cushman 1985, Appendix 2). The reduction or elimination of flow during the night can also impact the downstream drift of larval lake sturgeon. This type of operation is generally believed to impair recruitment in lake sturgeon (Haxton and Findlay 2009).
A “run-of-the-river” operation is based on constant flows through hydroelectric facilities that are equivalent to natural flows being received from upstream. Little or no storage of water is involved in this type of operation. “Run-of-the-river” operations are generally considered to have less impact on aquatic biota (Prosser 1986). When the Prickett hydroelectric facility was converted from a “peaking” to “run-of-the-river” operation, Auer (1996a) reported an increase in the number of spawning sturgeon (including more larger individuals and more fish in a reproductive ready state), and a reduction of time that sturgeon were located at the spawning site.
The alteration of flows outside of natural variability has a pronounced impact on sturgeon. Constant water flows trigger reproductive cues and allow large fish to migrate upstream (Auer 1994, 1996). Fluctuating water velocities were believed to cause a relocation response by spawning white sturgeon in the Kootenai River (Paragamian et al. 2002). Sudden increases in water discharge (both natural and artificial) during the winter can alter behaviour and maturation of gonads in some sturgeon species (Khoroshko 1967, Yelizarov 1968, Pavlov and Slivka 1972). High flows can also create bottom velocities which can preclude spawning or greatly reduce success (Kynard 1997).
Decreased water levels and flows in the spring can delay the upstream spawning migration of sturgeon (Friday and Chase 2005). Periodic high water flows can attract sturgeon into pools at the base of dams and spillways, thereby trapping them when water levels subside (Young and Love 1971, Brousseau and Goodchild 1989, Friday 2004). The rate at which flows are decreased (i.e., ramping) may not provide sufficient protection from trapping or stranding fish during flow reductions (Higgins and Bradford 1996). Climate and water flows during the spawning and incubation period are widely believed to influence year class strength (Votinov and Kasyanov 1978, Nilo et al. 1997, Jager et al. 2002, Randall and Sulak 2007). Highly variable flows from peaking operations can dislodge sturgeon eggs and larvae from their incubation sites (Swanson et al. 1990). Regulated flows, involving both lowering and raising of water levels, on the Wolf River, Wisconsin, following lake sturgeon spawning resulted in dessication of lake sturgeon embryos after being dislodged from the substrate and subject to air exposure (Kempinger 1988). Nocturnal flows are also required to ensure the downstream drift of sturgeon larvae which occurs predominantly at night. There is the need to develop flow enhancement and/or supplementation strategies below hydroelectric facilities especially during the spawning, incubation, and drifting periods of migratory fishes (Schilt 2007).
In addition to obstructing upstream fish movements, dams and hydroelectric facilities also represent barriers to downstream migration. Downstream migrants basically have three options when arriving at a dam or hydroelectric site: spill over the dam; entrain through the turbine; or utilize a turbine bypass system (when available). Most juvenile fish will pass downstream through spillways if outlet flow is sufficient. At the Dalles Dam on the Columbia River, larger (i.e., ≥95 cm total length) sturgeon have been recorded passing over the spillway with relatively low mortality (Parsley et al. 2007). Fish passing over spillways can be injured by rapid deceleration and pressure changes, abrasion, and impact from hitting the water. Small sturgeon are especially poor swimmers and are often unable to escape from an undertow below a dam. Water below spillways at high relief dams can become supersaturated and fish can sometimes develop gas bubble disease (Ruggles and Murray 1983, Counihan et al. 1998).
Mortality of downstream migrants is usually greatest during years of low flow when most of the river flow is passed through turbines (Prosser 1986). When fish pass through turbines, injuries and mortality result from pressure changes, mechanical contact with a turbine blade, or through shear forces and turbulence (Cada 1990). Small, juvenile fish seem especially prone to entrainment in turbines (Coutant and Whitney 2000). Killgore et al. (2001) reported mortality from shear stress was greater (> 75%) for smaller larvae (lake sturgeon and blue suckers, Cycleptus elongatus) than larger larvae (shovelnose sturgeon (Scaphirhynchus platornchus) and paddlefish (Polyodon spathula).
In some instances, such as the Mattagami River in northeastern Ontario, post-spawn sturgeon are drawn downstream through a spillway where they often become entrained in pools in the dewatered diversion channel below the dam (McCormick et al. 1990, Sheehan 1992, Seyler et al. 1996). Download full Report.