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

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COSEWIC
Executive Summary

Lake Sturgeon
Acipenser Fulvescens

Species Information


Description

The sturgeon family (Acipenseridae) contains 24 species, five of which are found in Canadian waters. Four of these are anadromous (spending part of the life cycle in freshwater and part in marine environments) and one, the lake sturgeon, is found only in fresh water. This species is one of Canada’s largest freshwater fishes with an extended snout, ventral mouth with four pendulous barbels, and a body covering of hard scutes and smaller denticles, rather than scales. This species reaches an age in excess of 100 years, lengths of up to 3 m and weights up to 180 kg.

 

Designatable Units

Based on the freshwater ecological areas used by COSEWIC and published genetic studies, eight designatable units were identified:
Western Hudson Bay (DU1);
Saskatchewan River (DU2);
Nelson River (DU3);
Red–Assiniboine Rivers – Lake Winnipeg (DU4);
Winnipeg River – English River (DU5);
Lake of the Woods – Rainy River (DU6);
Southern Hudson Bay – James Bay (DU7); and
Great Lakes – Upper St. Lawrence (DU8).

 

Habitat


Habitat Requirements

The lake sturgeon exists, for the most part, as a freshwater species, being found rarely in brackish water in larger rivers with access to the sea. Lake sturgeon are generally found in the shallow areas of lakes or larger rivers, moving into smaller rivers to spawn. They are a benthic (bottom dwelling) species that feeds over substrates of mud, sand or gravel. Lake sturgeon usually are found at depths of 5-10 m, but are found consistently in water deeper than 10 m in the Winnipeg River. Lake sturgeon are found in areas where water velocity does not exceed 70 cm/sec. Spawning sites usually are fast-flowing waters of 0.6-5 m in depth over hardpan clay, sand, gravel, rubble, cobble or boulders. Young-of-the-year have been observed resting on sand bars.


Habitat Trends

Habitat degradation and fragmentation from dam construction, including impoundments, have led to the loss of spawning sites and suitable rearing habitat throughout many parts of its range. Industrial pollution, agricultural runoff and siltation also have degraded and eliminated lake sturgeon spawning sites throughout its Canadian range.

 

Biology


General

The lake sturgeon is a large, long-lived, late-maturing species. Females generally are larger than males; however, there is a downward trend in size and age of both sexes wherever lake sturgeon are harvested.


Reproduction

Age at sexual maturity varies, but generally ranges from 18-20 years for males and 20-28 years for females. On average, males spawn every second year, and females every fourth to sixth year, in the spring when water temperatures reach 10-18˚C. Fecundity depends on size of the female; the number of eggs laid ranging from 50,000 to in excess of 1,000,000. The eggs hatch in 7-10 days and the larvae are negatively buoyant until formation of the swim bladder, about 60 days post-hatch. Larval drift occurs at night and begins about 2 weeks after the first spawning activities.


Survival

Larval and juvenile mortalities are high and few survive to adulthood. Adult mortality is low in areas not impacted by anthropogenic influences. Laboratory studies suggest that environmental modifications, through changes in habitat, could alter the type and quantity of food available and, consequently, have a detrimental effect on lake sturgeon survival.


Physiology

Lake sturgeon are adapted to water temperatures ranging from 3-24°C and can utilize, at least temporarily, habitats with suboptimal levels of oxygen. Lake sturgeon have been reported from Canadian estuaries and occasionally enter the brackish waters of Hudson Bay and Gulf of St. Lawrence.


Movements/Dispersal

Seasonal movements are not well known, but lake sturgeon probably move from shallower to deeper waters to avoid warmer temperatures in summer, returning to the shallows when temperatures decline in winter. Movements seem limited except for spawning migrations that can exceed distances of over 100 km; however, strong site fidelity is thought to occur with many spawning fish returning to the same sites year after year, although the occasional fish may wander from lake to lake to spawn.


Nutrition and Interspecific Interactions

Lake sturgeon feed on a wide variety of benthic fauna depending on seasonal and spatial availability as well as the nature of the benthos over which lake sturgeon feed. Adult lake sturgeon have few natural predators, for example, the incidence of lamprey scarring is rare in the Great Lakes and St. Lawrence River. Larval and juvenile lake sturgeon are preyed upon by other fish species. A number of parasites have been reported; however, none seem to be limiting lake sturgeon populations.


Behaviour/Adaptability

Lake sturgeon do not adapt readily to change, whether from exploitation or from habitat alterations.

 

Population Sizes and Trends

Within the last 3 generations (generation time for sturgeon is in the order of 35 to 54 years), lake sturgeon populations were severely reduced and in some cases extirpated in the southern part of the range primarily as a result of commercial overexploitation. More recently, some southern populations have shown some signs of recovery, but with the possible exception of Lake of the Woods and the St. Lawrence River, to nowhere near their historic level of abundance. Other southern populations remain at remnant levels, or are extirpated. Little historic and recent data on population sizes are available for northern populations around Hudson and James bays. The data available do suggest that unexploited northern populations may be relatively stable, but that exploited populations show the same pattern of decline as evidenced elsewhere throughout the range.

 

Limiting Factors and Threats

Limiting factors for lake sturgeon probably are related to climate, hydrology, and water temperature and chemistry. Threats include overexploitation (including poaching), dams, contaminants, habitat degradation and introduced species.

 

Special Significance of the Species

The lake sturgeon is one of the largest freshwater fish species in Canada. It, like all sturgeons, is a living fossil, and retains the cartilaginous skeleton and shark-like caudal fin of its ancestors of the Devonian period. In North America, lake sturgeon were scorned by the early settlers as a nuisance species, but commercial markets for smoked, dried, and fresh fish quickly developed after 1860 and peaked by 1900. In addition to its value as food, including caviar, the sturgeon was a source of oil, leather and isinglass (Harkness and Dymond 1961). The lake sturgeon always has been of special significance to Native peoples. Elders report that the sturgeon was a primary food source and was used in its entirety: five kinds of meat were obtained and other important products produced included containers made from skins, glue from swim bladders, paint binding agents, scrapers from scutes, and arrowheads from tail bones. To the Aboriginal groups of the eastern forests, the nutritional, material and spiritual significance of the sturgeon was analogous to the relationship between bison and tribes of the western plains. Lake sturgeon are long-lived and are thought to have a strong site fidelity for spawning and other habitat requirements making them sensitive indicators of the health of aquatic environments.

 

Existing Protection or Other Status Designations

The management of lake sturgeon and its habitat in Canada is through regulations pursuant to the Fisheries Act. Throughout its range in Canada, the lake sturgeon commercial, recreational and Aboriginal fisheries have been subject to special regulation. Currently, all 24 species of sturgeon in the world, including lake sturgeon, are considered to be at risk, and are listed on Appendix II of the Convention for International Trade in Endangered Species of Wild Fauna and Flora (CITES).