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

Habitat

Habitat Requirements

Historically, lake sturgeon were reported from large rivers and lakes (e.g. such as the Great Lakes, Lake Winnipeg, Sipiwesk Lake, the large inland delta on the Saskatchewan River at Cumberland House, Saskatchewan) and near the mouths of large rivers (Dick and Macbeth 2003). It is important to note that the concentration of lake sturgeon at the mouths of rivers is a short-term occurrence during spawning, and that for the remainder of their life they typically are dispersed in large lakes or river systems.

Recent detailed information on habitat use by lake sturgeon is limited. Adults are found in large rivers and lakes, generally at depths of 5-10 m over substrates of mud, clay, sand or gravel (Lane et al. 1996b; Page and Burr 1991, Nilo 1996). They consistently are found at depths greater than 10 m in the Winnipeg River (Erickson, pers. comm.). Lane et al. (1996b) indicated that, for Great Lakes populations, lake sturgeon usually were associated with silt substrate, while infrequently associated with gravel or sand substrates. Substrate type is considered to be important, since they feed on benthic (bottom dwelling) invertebrate fauna. However, studies by Choudhury et al . (1995) found sturgeon also fed on pelagic (living in the water column as opposed to on the bottom) Daphnia, and other studies have found that some individual sturgeon spent up to 70% of their time in the water column suggesting that some pelagic feeding occurs (Dick 2004). Seyler (1997a) reported that lake sturgeon habitat utilization was low where velocities exceeded 70 cm/sec.

Spawning habitats are fast-flowing waters, usually below waterfalls, rapids, or dams, over hardpan clay, sand, gravel, rubble, cobble or boulders (Lane et al. 1996c). In the Des Prairies River, these habitats are covered by a mix of fine- to medium-size gravel to boulders (LaHaye et al. 1992). Spawning also may occur on flat shelving sedimentary rock or freshly deposited riprap along river shores (Dick, unpubl. data). Most of the rivers used for spawning have falls that restrict upstream migrations; therefore, spawning sites for lake populations of sturgeon often are limited. LaHaye et al. (1992) found that lake sturgeon in the Montréal area used a wide variety of hard substrates for spawning and, depending on hydrological conditions, may utilize artificial spawning sites. Depth of water at spawning sites is quite variable, but usually is between 1 and 6 m of water (LaHaye et al. 1992; Lane et al. 1996c; Scott and Crossman 1998). Females have been observed spawning in 1 m of water at Landing River, northern Manitoba, and in the Embarass River, Wisconsin (Dick 2004). Manny and Kennedy (2002) described spawning habitats in depths ranging between 9 and 12 m in the connecting channels between lakes Huron and Erie. A large (3.6 ha) site has been recently discovered in the Lachine Rapids (St. Lawrence River) at Montréal. Egg deposition was found to be maximal in deep transparent water (up to 7 m), under average velocity in the water column between 1 and 2 m/s, over fine to average size gravel, with a mix of rocks and big rocks (La Haye et al. 2004). Ripe females have been captured in depths up to 10 m in the Winnipeg and Pigeon rivers below major rapids and falls, but usually in back eddies just off the main current (Dick 2004). Haxton (2006) reported similar findings in the Ottawa River, below the Chats Generating Station where spawning fish were taken on the side of the main channel where flows were not as great. Barth and MacDonnell (1999) observed sturgeon spawning below rapids in the Weir River, a tributary of the Nelson River in northern Manitoba in 1997 and 1998. Spawning location varied between years as a result of flow conditions dictated by a combination of Weir River discharge and Nelson River stage (i.e. volume and rate of flow in terms of what is happening as a result of the annual flood cycle, which varies in time and extent from year to year in relation to several factrs such as rain and snowfall).

The habitat reported for young-of-the-year (YOY) varies. They have been reported as resting on sand bars, fine gravel and cobble (Peake 1999). Seyler (1997a) reported YOY over smooth sand and gravel substrates in less than a metre of water. Lane et al. (1996a) indicated that YOY preferred 2.5 - 5+ m of water, were always associated with sand and silt, frequently associated with rubble and gravel, and infrequently associated with vegetation. In the lower Peshtigo River (a Lake Michigan tributary), YOY lake sturgeon used areas with sand substrates, low current velocities, and macroinvertebrate assemblages dominated by dipterans. Movement patterns indicated that declines in water temperature during fall months prompted fish to move downstream. With the exception of fall migration, home-range was found to be small (less than 500 m of longitudinal river length), with fish remaining in the same locations for several days to weeks. YOY showed greater activity after dark (Benson et al. 2005). In Black Lake (Michigan), two distinct mean depths (nearshore and deep offshore habitats) were used by yearling lake sturgeon, while juveniles utilized deep, flat-bottomed offshore habitat. Yearlings were associated with sand and organic substrate types, and juveniles with organic substrate types (Smith and King 2005).

In the St. Lawrence River, during fall, juvenile catch occurred more frequently at stations over bottoms of clay and gravel, in shallow depths (3-6m), and in areas with moderate water current (0.25-0.5 m/s). During summer, they were found in deeper water (6.1 to 9.0 m) and at higher current speed (0.5 to 0.75 m/s). Higher catch per unit of effort occurred on gravel substrate (Nilo 1996).


Habitat Trends

The importance of habitat loss to lake sturgeon populations is not well documented; the loss of habitat was considered far less important than overfishing in their decline.  In fact, many of the populations were reduced to remnant populations prior to major environmental perturbations affecting lake sturgeon habitat. Since these historic population crashes, prairie river systems have undergone extensive habitat degradation due to decreased flows and water quality as a result of irrigation and the construction of dams. Fluctuating flow in the Cumberland delta, resulting from the construction of a dam on the Saskatchewan River, has negatively impacted lake sturgeon populations downstream of the dam. Construction of the Lockport Dam on the Red River for navigation purposes, and the alteration of the annual flow regime to maximize storage of water in the spring on the Assiniboine River, probably has affected the potential for spawning runs in these rivers. In other rivers, like the Roseau, construction of drainage ditches has increased water flow and suspended sediments in the spring during spawning times, but reduced flows following spring flooding. This has led to reduced juvenile feeding habitat as a result of lower water levels following spawning. Generally, impoundments have altered flows and limited pristine habitat (Figure 13). Studies on the Winnipeg River indicate that lake sturgeon distribution, especially of juveniles, is positively correlated with unaltered river habitat (Dick 2004). The Moose River basin is one of the most fragmented river systems in North America, but the overall impact on the region’s lake sturgeon populations is unknown (Seyler 1997a). The combined impacts of overexploitation, increased industrialization, pollution, species invasions and habitat loss in the Great Lakes region make it difficult to establish current cause and effect relationships in lake sturgeon populations.


Figure 13: Locations of Dams and Barriers within Lake Sturgeon Range in Canada

Figure 13: Locations of dams and barriers within lake sturgeon range in Canada (map courtesy Ron Hempel).

Map courtesy Ron Hempel.

Habitat fragmentation is a major concern for this long-lived migratory fish that utilizes a variety of habitats throughout its life (Robitaille et al. 1988, Auer 1996a). In the St. Lawrence River, recent experimental fishing data confirm that the Lac Saint-François sturgeon group, upstream of Lac Saint-Louis, considered as depleted in the 1940s (Cuerrier and Roussow 1951), the 1960s (Joliff and Eckert 1971) and the 1980s (Dumont et al. 1987), is still at very low abundance. Tagging studies in the 1940s indicate that lake sturgeon was then able to migrate along the St. Lawrence River, from the limits of the brackish waters up to at least Brockville (Ontario) (Roussow 1955b). Depletion of the Lac Saint-François lake sturgeon group can likely be attributed to the combined effects of the gradual construction of dams at both extremities of the lake between 1912 and 1958 (Morin et al. 1998) and to the overfishing of the residual stock.