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

Update
COSEWIC Status Report
on the
Lake Sturgeon
Acipenser fulvescens
in Canada
2006

Species Information

Name and Classification

Class:
Actinopterygii
Order:
Acipenseriformes
Family:
Acipenseridae
Genus:
Acipenser
Scientific name:
Acipenser fulvescens Rafinesque 1817 (Nelson et al. 2004)
Common name
 English:
Lake Sturgeon (Nelson et al. 2004)
 French:
Esturgeon jaune (Nelson et al.2004)
Other common names
 English:
Rock, Common, Red, Ruddy, Ohio, Shell-back, Bony, Freshwater, Smooth-back, Rubbernose, Black, Dog Face, Bull-nosed and Great Lakes Sturgeon.
 French:
Camus pour les adultes; escargot, maillé and charbonnier for juveniles.

The phylogeny and biogeography of the sturgeon family (Acipenseridae) have been reviewed by Bemis et al. (1997) and Choudhury and Dick (1998). The family contains 24 species, five of which are found in Canadian waters (Scott and Crossman 1998). Four of these species are anadromous (spending part of the life cycle in freshwater and part in marine environments) and one, the lake sturgeon (Figure 1), lives almost exclusively in freshwater and is one of Canada’s largest freshwater fish (white sturgeon, Acipenser transmontanus, may attain greater size, but some populations may be anadromous). Roussow (1955a) recognized two forms or morphs, brown or lake sturgeon,A. fulvescens acutirostris, and the black or rock sturgeon, A. f. obtusirostris; however, these subspecific names are not valid as they have been used for forms of A. ruthenus Linneaus 1758 and are unavailable as names for all other species (Eschmeyer 2005).


Figure 1: Lake sturgeon, Acipenser fulvescens, 76 cm; St. Lawrence River, Leeds County, Ontario, May 19-20, 1968

Figure 1: Lake sturgeon, Acipenser fulvescens, 76 cm; St. Lawrence River, Leeds County, Ontario, May 19-20, 1968.

ROM 25887. Drawing by Anker Odum, from Scott and Crossman (1973) used with permission.


Description

Sturgeons, as a group, are little altered from their ancestral form. They are cartilaginous, dorso-ventrally flattened bottom-dwelling fishes. Conspicuous external bony scutes are very pronounced on larval and juvenile sturgeon, but are less pronounced in larger fishes, as they become embedded in the body wall. Lake sturgeon have a ventral mouth, a pointed snout and four pendulous barbels that are used to sense the environment and to locate food (Harkness and Dymond 1961). They also are characterized by a heterocercal tail and ganoid scales along the caudal fin (Scott and Crossman 1998). Generally, lake sturgeon are dark to light brown or grey in colour on the back and sides, with a lighter coloured belly, but other names using a colour designation include red, ruddy or black with the black sturgeon often referred to as river sturgeon by Aboriginal Elders. Older lake sturgeon generally are a uniform brown colour, while younger sturgeon may have irregular black patches on a brown background. They have a characteristic large, thick-walled swim bladder that helps maintain buoyancy. However, unlike other fishes where the swim bladder develops within the first few days post-hatch, formation of the lake sturgeon swim bladder occurs up to 60 days post-hatch (T.A. Dick, Department of Zoology, University of Manitoba, Winnipeg, MB; unpublished data). On hatching, lake sturgeon have a rounded head end, lack a snout and mouth parts and are negatively buoyant. As the snout develops, mouthparts and microscopic teeth form (Dick 1995).

The largest lake sturgeon recorded was taken in the Roseau River of Manitoba, weighing 185 kg and was estimated to be 4.6 m in length (Waddel 1970; Stewart and Watkinson 2004). The oldest lake sturgeon recorded, caught in Lake of the Woods, Ontario, was determined to be 154 years old and weighed 94 kg (Mackay 1963). Today, the largest lake sturgeon usually are less than 40 kg (Scott and Crossman 1998).


Designatable Units

The identification of designable units in lake sturgeon was assessed based on the four criteria identified by COSEWIC (2003).


Criterion 1) Named Subspecies or Varieties

Lake sturgeon are morphologically diverse and some colour variants have been formally named to the subspecific level; however, these subspecies are not considered to be valid (Scott and Crossman 1998). Numerous local names imply great phenotypic difference, but no formal studies have been conducted. Observations have confirmed the traditional knowledge of Elders that black sturgeon are more common in rivers, and the off-white phenotype occurs with greater frequency in lakes and river mouths (H. Mackay, Elder, Berens River, MB; personal communication). According to Elders, the off-white phenotypes are rare, and the white phenotype is even rarer occurring at a rate of one fish in 20,000 (R. Bruch, Wisconsin Department of Natural Resources Oshkosh, WI; personal communication). This phenotype now may be absent from many Canadian populations due to population declines, fragmentation and extirpations. To date, these rare white phenotypes have been found only in the Pigeon and Winnipeg rivers (Dick, et al. 2003). Clearly, traditional and local knowledge indicates that phenotypic differences have been observed for a long time between river and large lake populations, but these probably represent differences at the level of life history types rather than formal subspecies. Therefore, no formal basis exists for designatable units at the subspecific level.


Criterion 2) Units Identified as Genetically Distinct

Studies of mitochondrial DNA (mtDNA) variation in lake sturgeon have revealed low haplotype diversity. Guénette et al. (1993) detected three restriction site haplotypes in a study of lake sturgeon from Quebec. Haplotype frequencies did not differ significantly among the sites in the St. Lawrence River drainage (St. Lawrence River, Ottawa River, Lac des Deux Montagnes), or between these sites and the Waswanipi River in the James Bay drainage, possibly because sample sizes were small (8-12 fish per location). Ferguson et al. (1993) also detected two mtDNA haplotypes in the Moose River basin (James Bay drainage) in Ontario. Haplotype frequencies did not vary significantly among several locations in the drainage, including the Mattagami, Groundhog and Abitibi Rivers, but were significantly different in the North French River, suggesting the presence of a distinct population in this tributary. Ferguson and Duckworth (1997) used the same approach to study mtDNA variation across a much broader geographic region, including Moose River basin and Waswanipi River (James Bay drainage), Lower Nelson River and Rainy River (Hudson Bay drainage), and 10 locations in the Great Lakes – St. Lawrence drainage ranging from the Sturgeon River (Lake Superior) to Québec City. Again, two haplotypes accounted for the great majority of samples; southern populations were made up almost exclusively of haplotype 1, whereas the three northern populations (Waswanipi, Moose and Lower Nelson Rivers) exhibited a mix of haplotypes 1 and 2. The authors suggested this distribution of haplotypes reflected differential dispersal of sturgeon from two glacial refugia, Mississippian (haplotype 1) and Missourian (haplotype 2).

Studies of variation at nuclear microsatellite loci have detected much more diversity within and among lake sturgeon populations. For example, a recent study of variation at three microsatellite loci found that populations of lake sturgeon from the Saskatchewan, Nelson, Winnipeg and Rainy rivers represent genetically distinguishable populations (Robinson and Ferguson 2001; M. Robinson, Department of Zoology, University of Guelph, Guelph, ON; personal communication). The three microsatellite loci exhibited moderately high levels of polymorphism, with 7-10 alleles per locus and mean expected heterozygosities within population samples of 0.60-0.74. Pairwise population differentiation tests based on genic and genotype frequencies, and pairwise FST tests detected significant differences (p<0.001) between the river systems tested, but not between samples within river systems (Robinson and Ferguson 2001). Estimates of pairwise FST between river systems ranged from 0.016 between the Nelson and Winnipeg Rivers to 0.110 - 0.178 between Lake of the Woods and locations in the Saskatchewan River (Table 1).

 

Table 1a: Genetic characteristics of microsatellite loci analyzed in adult lake sturgeon from Canadian Rivers
Locus & CharacteristicPopulations SampledTotals
OntarioManitobaSaskatchewan
L. WoodsRainy R.Nelson R.Winnipeg R.Sask. R. PasTorch RiverBigstone Rap.C. AnglingThe Forks
AFU 68 - NFish254050503314244640322
AFU 68 - NAlleles465544655 
AFU 68 - Size Range (bp)115-135115-135115-139111-135115-135115-135111-135111-135111-135111-139
AFU 68 - HObs0.16000.14290.38000.50000.60610.42860.65380.52000.5750 
AFU 68 - HExp0.32240.31760.50120.48000.69790.70640.66770.58000.7423 
AFU 68b - NFish254250503314265040330
AFU 68b - NAlleles677875786 
AFU 68b - Size Range (bp)168-196168-196160-202160-202160-202160-188160-192160-202160-192160-202
AFU 68b - HObs0.76000.66670.80000.80000.60610.50000.57690.66000.5500 
AFU 68b - HExp0.71680.74430.74700.77620.70480.52930.51040.60740.5538 
SPL 120 - NFish254250503314265040330
SPL 120 - NAlleles768655555 
SPL 120 - Size Range (bp)252-288252-284248-288252-284252-284252-284252-284252-284252-284248-288
SPL 120 - HObs0.88000.66670.80000.80000.87880.78570.80770.82000.6250 
SPL 120 - HExp0.78840.72360.79460.74120.78970.70070.77000.79000.7355 
Mean - HObs0.60000.49210.66000.70000.69700.57140.67950.66670.5833 
Mean - HExp0.60920.59520.68090.66580.73080.64550.64940.65910.6787 

Populations are listed by province; all locations for Saskatchewan are in the Saskatchewan River system. NFish refers to the number of fish analyzed per locus per population. HObs and HExp refer to the observed and expected frequencies of heterozygotes [reproduced from Robinson and Ferguson (2001) by permission].

 

Table 1b: Pairwise FST Comparisons Between Sturgeon Population Samples
 WRSCSFSPBRLWRR
NR0.0163*0.0200*0.0572*0.0285*0.0591*0.0423*0.0171*
WR-0.0461*0.0974*0.0499*0.0958*0.0624*0.0397*
SC--0.01460.00300.00810.1096*0.0660*
SF---0.00970.00040.1630*0.1176*
SP----0.00640.1066*0.0821*
BR-----0.1780*0.1353*
LW------0.0062

Population samples are coded as follows: NR = Nelson River, MB, DU3; WR = Winnipeg River, MB, DU5; SC = Saskatchewan River Centre Angling, SK, DU2; SF = Saskatchewan River Forks, SK, DU2; SP = Saskatchewan River Pas, MB, DU2; BR = Saskatchewan River Bigstone Rapids, SK, DU2; LW = Lake of the Woods, ON, DU6; RR = Rainy River, ON, DU6 [reproduced from Robinson and Ferguson (2001) by permission].

* = Significant at Bonferonni (Rice, 1989) adjusted p < 0.001786.

McQuown et al. (2003) examined lake sturgeon from six locations in the St. Lawrence/Great Lakes region and the Mattagami River in the Hudson Bay drainage using seven microsatellite loci. Based on a multivariate factor analysis of Nei’s (1972) genetic distance they identified three distinct groups: (1) Mattagami; (2) Menominee/Wolf (Lake Michigan-Wisconsin); and (3), St. Lawrence/Des Prairies/Niagara/Erie (lower Great Lakes).

Welsh and McClain (2004) expanded on the McQuown et al. (2003) study by analyzing the same samples plus samples from additional locations in Lakes Superior, Huron and Erie with a total of 13 microsatellite markers. This study revealed extensive structuring of sturgeon populations; most locations differed significantly from other spawning locations. Several major groupings were evident, although the group affinities of some populations varied depending on the method of analysis used. The Mattagami River and Rainy River (Hudson Bay drainage) appeared divergent from all St. Lawrence/Great Lakes populations (FST = 0.13 - 0.25). Sturgeon populations within Lake Superior appeared highly diverse and clustered in three groups. One group, the Bad and White Rivers (southern Lake Superior), was relatively divergent from all other Great Lakes populations (FST = 0.09 - 0.17). Three northern Lake Superior tributaries, the Kaministiquia, Black Sturgeon and Pic Rivers formed a distinct cluster in a factorial correspondence analysis, but showed loose affinities with the Mattagami/Rainy and Bad/White clusters in a neighbour-joining analysis of Cavalli-Sforza & Edwards chord distances (see Figures 2 and 3). Two other Lake Superior rivers, the Batchawana and Goulais Rivers, clustered with populations from the other Great Lakes and St. Lawrence River. Within this last group, genetic differentiation was weaker (Fst = 0.01- 0.08) and not significant in all pairwise comparisons, and there was no consistent relationship between genetic distance and geographic distance separating populations; for example, samples from the St. Lawrence River and Rivière Des Prairies (a St. Lawrence tributary) clustered with the Wolf and Menominee Rivers from Lake Michigan (Figures 2, 3).


Figure 2: UPGMA Tree Showing Genetically Similar Groups, Based on Nei’s Unbiased Genetic Distance (1978)

Figure 2: UPGMA tree showing genetically similar groups, based on Nei’s unbiased genetic distance (1978).

The top scale represents genetic distance values. Numbers correspond to bootstrap values, or the percentage of trees (out of 1000) where the corresponding split in the tree is confirmed. Only bootstrap values greater than 50% are displayed.


Figure 3: Neighbour-joining Tree Showing Genetically Similar Groups, Based on Cavalli-Sforza and Edwards (1967) Chord Distance

Figure 3: Neighbour-joining tree showing genetically similar groups, based on Cavalli-Sforza and Edwards (1967) chord distance.

This tree results from an approach similar to the one used to generate Figure 2 above; however, there are differences between the genetic distance measures and the assumptions used in tree configuration. Numbers correspond to bootstrap values, or the percentage of trees (out of 1000) where the corresponding branch on the tree is confirmed. Only bootstrap values greater than 50% are displayed (adapted from Welsh and McLean 2004).

The studies noted above used different suites of genetic markers and surveyed different portions of the geographic range of lake sturgeon. No study has examined lake sturgeon from all river basins or areas within the geographic range of the species with a common set of genetic markers. Inherited traits such as morphology, life history and/or behaviour also can be used to support designatable units under this criterion. Unfortunately, appropriate studies across the geographic range of lake sturgeon are also lacking; however, Fortin et al. (1993) suggested that populations probably differ by watershed and that there also may be differentiation of sympatric populations in larger watersheds, a suggestion consistent with the results of the genetic studies cited above.

Because of their fragmented nature, the genetic studies carried out to date on lake sturgeon provide no specific prescription for designatable units across the range of the species, but they do suggest at least one important generality. Populations occurring in different major drainages appear invariably to be genetically distinct from each other. Within drainages, the situation becomes more complex, with evidence of multiple genetically distinguishable populations within some drainages (e.g. Moose River, Saskatchewan/Nelson/Winnipeg/Rainy River complex, Lake Superior), but weak or no differentiation across regions as broad as the lower Great Lakes-St. Lawrence. Therefore, designatable units could reasonably be defined at the level of major drainages, with the understanding that recognizable sub-units occur within at least some drainages, and that additional genetic information could result in the identification of even more units, or the elevation of particular sub-units to DU status. At the other extreme, arguments could be made for minimal, biologically significant differentiation of units within the species with one or, at best, two groups being recognized [i.e. the species in the first, and the likelihood of two glacial refugial forms in the second instance (see Ferguson and Duckworth 1997)], although definitive studies for the latter option are lacking.


Criterion 3) Units Separated by Major Range Disjunction

Excluding isolation on a local basis as a result of presence in different drainage basins, there are no disjunctions apparent in the geographic range of this species in Canada (Scott and Crossman 1998). Thus, this criterion cannot be used to differentiate designatable units.


Criterion 4) Units Identified as Biogeographically Distinct

Lake sturgeon are found in four of the 14 aquatic ecozones (AE) recognized for Canadian fresh waters (COSEWIC 2003; Figure 4). These are: AE 3 – Southern Hudson Bay-James Bay, AE 4 – Saskatchewan-Nelson, AE 5 – Western Hudson Bay, and AE 10 – Great Lakes-Upper St. Lawrence. Therefore, at least four recognizable designatable units are present within the lake sturgeon range based on this criterion alone.


Figure 4: COSEWIC National Freshwater Ecozones (COSEWIC 2003)

Figure 4: COSEWIC National Freshwater Ecozones (COSEWIC 2003).

Prepared by N.E. Mandrak, 03/06/03.

Available genetic evidence for lake sturgeon supports the primary separation of designatable units based upon ecozones and tends to further differentiate some units within several of the ecozones. Evidence for designating units within the ecozones is limited primarily by the lack of appropriate studies that include samples from distinct sub-basins of the ecozones. In available studies, a hierarchy of differences typically is found with samples from geographically close locations being less distinct than those from more distant locations within the same river basin. This is consistent with the knowledge available for other freshwater fish species for which better data and sampling coverage exists. Probably, despite the likelihood of long-distance migrations in unimpeded river systems, significant sub-structuring of lake sturgeon occurs within each of the major units designated below. Therefore, eight distinct designatable units are identified (Table 2, Figures 5, 6), but many more undoubtedly are present:

  1. Western Hudson Bay;
  2. Saskatchewan River;
  3. Nelson River;
  4. Red-Assiniboine Rivers-Lake Winnipeg;
  5. Winnipeg River-English River;
  6. Lake of the Woods-Rainy River;
  7. Southern Hudson Bay-James Bay; and
  8. Great Lakes-Upper St. Lawrence.

 

Table 2. Structure and composition of designatable units of lake sturgeon.
DU Ecozone CriterionDU (Ecozone + Genetics)
NameCompositionNameCompositionDU Number
A. Western Hudson BayChurchill, and any related rivers in NW/NE ManitobaWestern Hudson BayChurchill River1
B. Saskatchewan/ Nelson/Assinboine/ Red/Churchill Rivers/L. WinnipegSaskatchewan/Nelson/ Assinboine/Red/Churchill Rivers including all drainages to L. Winnipeg, Lake of the Woods and all related southern NW drainages of Ontario (Rainy, Winnipeg, etc.)Saskatchewan RiverSaskatchewan R upstream of L. Winnipeg; all drainages west to east-central Alberta2
B. Saskatchewan/ Nelson/Assinboine/ Red/Churchill Rivers/L. WinnipegSaskatchewan/Nelson/ Assinboine/Red/Churchill Rivers including all drainages to L. Winnipeg, Lake of the Woods and all related southern NW drainages of Ontario (Rainy, Winnipeg, etc.)Nelson River.Nelson R. downstream of L. Winnipeg, and all related drainages to Nelson3
B. Saskatchewan/ Nelson/Assinboine/ Red/Churchill Rivers/L. WinnipegSaskatchewan/Nelson/ Assinboine/Red/Churchill Rivers including all drainages to L. Winnipeg, Lake of the Woods and all related southern NW drainages of Ontario (Rainy, Winnipeg, etc.)Red-Assiniboine Rivers - Lake WinnipegL. Winnipeg, Red, Assiniboine and all eastern tributary rivers to L. Winnipeg (excluding Winnipeg R.)4
B. Saskatchewan/ Nelson/Assinboine/ Red/Churchill Rivers/L. WinnipegSaskatchewan/Nelson/ Assinboine/Red/Churchill Rivers including all drainages to L. Winnipeg, Lake of the Woods and all related southern NW drainages of Ontario (Rainy, Winnipeg, etc.)Winnipeg River-English RiverWinnipeg R. upstream to Kenora, English-Wabigoon river system5
B. Saskatchewan/ Nelson/Assinboine/ Red/Churchill Rivers/L. WinnipegSaskatchewan/Nelson/ Assinboine/Red/Churchill Rivers including all drainages to L. Winnipeg, Lake of the Woods and all related southern NW drainages of Ontario (Rainy, Winnipeg, etc.)Lake of the Woods- Rainy RiverAll Rainy River, Lake of the Woods tributaries upstream of Kenora6
C. Southern Hudson and James BayAll drainages of northwestern Quebec, Ontario and northeastern Manitoba that drain to Hudson/James baysSouthern Hudson Bay-James BayAll drainages of Quebec and northern Ontario to Hudson/James bays; Gods and Hayes rivers of northeastern Manitoba7
D. Great Lakes/Upper St. LawrenceAll drainages to and including the Great Lakes and L. Nipigon then eastwards to include all tributary systems to St. Lawrence RiverGreat Lakes- Upper St. LawrenceAll drainages to and including the Great Lakes and St. Lawrence River8

 


Figure 5: Flow diagram of decisions made in establishing designatable units (DU) in lake sturgeon, Acipenser fulvescens

Figure 5: Flow diagram of decisions made in establishing designatable units (DU) in lake sturgeon, Acipenser fulvescens.

The top box identifies the major criteria (A-C) used to establish DUs using the stepwise procedure in Taylor(2005) and the criteria in the COSEWIC S&P Manual. NA = “not applicable” for decision making (no evidence or data not available). In this chart, DUs were first identified by occupancy in distinctive freshwater ecozones (criterion C) and resulted in DU1, 2-6, 7, and 8. Subsequently, some DUs (e.g., DUs 2, 3, 5, and 6) were established by the presence of significant genetic differentiation within ecozones. DU4 is recognized as distinct from DU5 owing to the presence of dams near the Winnipeg River outlet to Lake Winnipeg that reinforce a probable historical disjunction due to impassable rapids - a hypothesis requiring testing genetically.

Notes: Genetic distinction (criterion D) is based on significant pairwise differences (P < 0.001, 3 loci) in microsatellite DNA allele frequencies between DUs 2, 3, 5, and 6. All sample sizes within DUs at least 50 (Robinson and Ferguson 2001). Further details are provided in the status report.


Figure 6: The Designatable Units Used in this Report

Figure 6: The designatable units used in this report.

Dark lines represent divisions between ecozones used by COSEWIC. Light lines represent subdivision of ecozone into further designatable units based on available genetic information. DU1 - Western Hudson Bay; DU2 Saskatchewan River, DU3 - Nelson River; DU4 - Red-Assiniboine rivers-Lake Winnipeg; DU5 - Winnipeg River-English River; DU6 - Lake of the Woods-Rainy River; DU7 - Southern Hudson Bay-James Bay; DU8 - Great Lakes-Upper St. Lawrence.

The above units are described as follows:


DU1 - Western Hudson Bay

Based upon presence in the Western Hudson Bay ecozone (Criterion 4, COSEWIC Aquatic Ecozone 5), lake sturgeon of the Churchill River system of northern Manitoba and Saskatchewan (Figure 7) are considered a distinct designatable unit (DU1).


DU2 - Saskatchewan River

Fish within the Saskatchewan-Nelson ecozone are distinct at this level (Criterion 4, COSEWIC Aquatic Ecozone 4); however, existing genetic studies (Robinson and Ferguson 2001) indicate that fish from the Saskatchewan River upstream of the Grand Rapids Dam at Lake Winnipeg (Figure 7) comprise a distinct population (Criterion 2) within this ecozone that logically includes all immediate drainages to this system in western Manitoba, central Saskatchewan, and east-central Alberta.


Figure 7: Lake Sturgeon Sites in Alberta, Saskatchewan and Manitoba Referred to in Text

Figure 7: Lake sturgeon sites in Alberta, Saskatchewan and Manitoba referred to in text.

1. South Saskatchewan River; 2. North Saskatchewan River; 3. Forks of the Saskatchewan; 4. Cumberland House, Saskatchewan River; 5. Sandy Bay, Upper Churchill River; 6. Lower Churchill River; 7. Landing River, Nelson River; 8. Sipiwesk Lake, Nelson River; 9. Hayes River; 10. Gods River; 11. The Pas, Saskatchewan River; 12. Lake Winnipeg; 13. Poplar River; 14. Berens River; 15. Pigeon River (Round Lake); 16. Bloodvein River; 17. Brandon, Manitoba; 18. Assiniboine River; 19. Red River; 20. Winnipeg River.


DU3 - Nelson River

Fish from the Nelson River, downstream of Lake Winnipeg to the Hudson Bay coast, comprise a genetically distinct group (Robinson and Ferguson 2001) that includes all immediate drainages to this system (Figure 7) in northeastern Manitoba (Criterion 2). Telemetry studies carried out on the Nelson River by Manitoba Hydro from 1986-1992 suggest that lake sturgeon are fairly sedentary within the river and movements are related to routes between spawning and foraging habitat (MacDonell 1992).


DU4 Red - Assiniboine Rivers-Lake Winnipeg

Although genetic studies conducted to date (Robinson and Ferguson 2001; Robinson pers. comm.) have not included samples from the south-central areas of Manitoba (primarily due to the absence of extant populations), lake sturgeon from Lake Winnipeg, including such tributaries as the Bloodvein, Pigeon, Poplar, and Berens rivers (lake sturgeon were never known from Lake Winnipegosis or Lake Manitoba) as well as the Red-Assiniboine, and Roseau rivers (Figure 7) probably constitute(d) a designatable unit distinct from those indicated above (DU3), although some sub-structuring is likely within this large and diverse area, and also between lacustrine and riverine fish, if such represent distinct life history types. Most of the large spawning populations once associated with distinct regions within this area (e.g. Assiniboine, Red and Roseau rivers) are lost, and recent stocking and recovery efforts may have mixed fish from several sub-basins into different areas. Thus, appropriate testing of population structuring among putative groups within DU4 probably is impossible.


DU5 Winnipeg River-English River

Fish from the Winnipeg River system of southeastern Manitoba are genetically distinct from those of the Saskatchewan and Nelson rivers, and thus constitute a designatable unit (DU5). Other southern and eastern Lake Winnipeg tributaries are included in DU4, but the fish in the Winnipeg River, the largest tributary of Lake Winnipeg, were historically isolated from those in Lake Winnipeg by the Lower Pine Falls and Great Falls (Figures 7, 8). In addition a number of dams (Figure 8) have further segmented the population with little mixing occurring for almost 100 years (W. Lysack, Manitoba Conservation, Winnipeg, MB; personal communication). The English River is likewise segmented by a series of rapids and falls and dams (Figure 8).


Figure 8: Water Control Within the Winnipeg River Watershed (Lower Reaches)

Figure 8: Water control within the Winnipeg River watershed (lower reaches).

Hydro dams:
Pinawa
1906-1951
Pointe du Bois
1911
Great Falls
1923
Seven Sisters & Slave Falls
1931
Pine Falls
1951
McArthur
1954


DU6 Lake of the Woods-Rainy River

Although genetically distinct at one level from fish from the Winnipeg River, the distinction for fish from the Rainy River system of Ontario is also considered to be biologically significant at this time, even though this system ultimately drains into the Winnipeg River. Falls and dams along the Winnipeg River (Figure 7), particularly the Norman Dam located at the mouth of the river, impede passage of sturgeon from Lake of the Woods and prevent upstream movement (Martin Erickson, Fish Habitat Specialist, Manitoba Water Stewardship, Fisheries Branch, Winnipeg, MB, personal communication). According to McAughey (Scott McAughey, Ontario Ministry of Natural Resources, Kenora, Ontario; personal communication) it is unlikely the predam rapids at Norman prevented movement of lake sturgeon. However, falls lower down on the system probably did.

Thus, fish from Rainy River System of northwestern Ontario (Figures 7-9), including those from Lake of the Woods, are provisionally included in DU6. There are no genetic data available for the populations of lake sturgeon upstream of the Rainy River within this designatable unit (Rainy Lake, Seine River, Namakan Reservoir, Namakan River, Little Turtle Lake, Lac La Croix, Loon Lake, SturgeonLake, Russell Lake, Tanner Lake and the Maligne River).


DU7 Southern Hudson Bay-James Bay

Fish within the Southern Hudson Bay and James Bay ecozone are widely distributed among many large river systems of northeastern Manitoba, northern Ontario and northwestern Quebec (Figure 9), and are distinct from those found in the Great Lakes basin. DU7 includes lake sturgeon from the Gods and Hayes rivers of northeastern Manitoba although, based on tagging studies (Barth and MacDonnell 1999), these probably mix with fish in the estuary shared by these rivers and the Nelson River. Populations from all three river systems are not very extensive however (see Population sizes and trends below). In Quebec, the eastern limit of distribution of the lake sturgeon in these drainage basins coincides with the eastern limits of the ancient Tyrell Sea and of the glacial lake Ojibway-Barlow. Natural falls and longitudinal gradient of the rivers probably stopped its progression eastward during the last deglaciation period.

Although many of the populations residing in individual rivers across the ecozone probably are genetically distinct from one other, evidence is limited at best. The genetic work that has been conducted to date has tended to focus upon samples from tributary river systems within a basin and these, statistically, were not significantly different in most cases. Therefore, until more comprehensive evidence is available, all lake sturgeon from this ecozone are included in DU7.


DU8 Great Lakes-Upper St. Lawrence

Fish within the Great Lakes-Upper St. Lawrence ecozone are genetically distinct from those found in southern Hudson Bay drainages (Figure 9), and probably also are distinct from those in western drainages, although specific tests of the latter hypotheses have not been conducted. Available evidence suggests the likelihood of several designatable units within this area. Fish from Lake Superior, including those of Lake Nipigon and all related drainages, are generally distinct from populations in the lower Great Lakes; however, two Lake Superior populations (Batchawana, Goulais) grouped with populations from Lake Huron, and the lower Great Lakes-St. Lawrence. Therefore, the populations in the Great Lakes-Upper St. Lawrence ecozone are considered to be a single designatable unit. More comprehensive genetic studies will be needed to clarify the biologically significant sub-structuring within this ecozone, and probably will lead to the identification of additional designatable units in the ecozone.


Figure 9: Lake Sturgeon Sites in Ontario and Quebec Referred to in Text

Figure 9: Lake sturgeon sites in Ontario and Quebec referred to in text.

1.Lake of the Woods, Rainy River; 2. Kaministiquia River; 3. Nipigon River; 4. Nipigon Bay; 5. BlackSturgeon River; 6. Gravel River; 7. Big Pic River; 8. Michipoten River; 9. Goulais River; 10. Lake St. Clair; 11. Lake Erie; 12. Huron Bay; 13. Lake Simcoe; 14. Trent River; 15. Lake Ontario; 16. Salmon River; 17. St. Lawrence River; 18.Massena, New York; 19. Lac St. François; 20. Lac St. Louis; 21. Lac Des Deux Montagnes; 22. Ottawa River; 23. Madawaska River; 24. Bonnechère River; 25. Lake Nipissing; 26. Timiskiming; 27. Missinaibi River; 28. Groundhog and Matagami rivers; 29. Kenogami River; 30. Cheepash River; 31. Kwatabochegon River; 32. Abitibi River and Otter Falls; 33. North French River; 34. Moose River; 35. Harricana River; 36. Waswanipi River; 37. Nottaway River; 38. Broadback; 39. Rupert River; 40. Eastmain River; 41. La Grande River, 42. Lac St. Pierre.