© 2004 by CRC Press LLC chapter five Impact of new reservoirs Michel Legault Société de la faune et des parcs du Québec Jean Benoît Société de la faune et des parcs du Québec Roger Bérubé Hydraulique et Environnement, Hydro-Québec Contents Introduction Transformations to ecosystems Water quality Plankton Benthos Fish abundance Climatic warming and reservoirs Impacts of reservoirs use on lake trout reproduction Characteristics of reproduction sites Effects of raised water level Effects of water level fluctuations Management recommendations for lake trout in reservoirs Integrated management of water and wildlife Introduction of a strain of deep-spawning lake trout Creating deep-zone spawning areas Supplemental stocking Restricting harvest Conclusions References Introduction Even though there are many reasons for creating reservoirs (such as drinking water supply, irrigation, or stream flow control), production of hydroelectricity (Figure 5.1) is the main reason for the existence of reservoirs on the Precambrian Shield. Exploitation of Canadian © 2004 by CRC Press LLC hydroelectric potential began in the last century and has advanced northward like a wave that is now cresting in the midnorthern latitudes (Rosenberg et al., 1987). Already, the total area of boreal reservoirs in North America is similar to that of Lake Ontario (Rudd et al., 1993). The environmental impacts that result from the creation of reservoirs are numerous and include accumulation of sediments, shore erosion, and accumulation of mercury in fish and other organisms. There are upwards of 100 reservoirs in Québec, 68 of which are known to support lake trout populations. These represent 7.4% of the province's lake trout lakes. In Ontario, the areas with the most concerns about reservoirs and water level variations are the Algonquin and Eastern regions (Lewis et al., 1990). Together they comprise nearly 22% of Ontario’s lake trout lakes. The lake trout Salvelinus namaycush is among the most studied species in North America with regard to reservoir management. Lake trout have great difficulty adapting to lakes with regulated water levels or to reservoirs used for hydroelectric generation purposes (Martin, 1955; Wilton, 1985; Gendron and Bélanger, 1993; Benoît et al., 1997). The change in water level, the resulting surface area and type of substrate of the flooded lands, the seasonal drawdown regime employed, and the lotic or lentic origin of the reservoir are some of the many factors affecting lake trout’s adaptation in reservoirs (Machniak, 1975; Evans et al., 1991). Among the foregoing factors, drawdown is often pinpointed as the cause of the lake trout's adaptation problems, as it has repercussions on two aspects of the species’ vital cycle: reproduction success and larvae survival (Martin, 1955; Wilton, 1985; Gendron and Bélanger, 1993). This chapter reviews major modifications made to lake trout ecosystems by the cre- ation of reservoirs on the Precambrian Shield. It also discusses impacts of drawdown on the reproduction of lake trout and suggests management alternatives. Figure 5.1 Reservoir for production of hydroelectricity. © 2004 by CRC Press LLC Transformations to ecosystems As a result of reservoir creation and management practices, temporary and permanent transformations to ecosystems will occur. These transformations can be of greater or lesser significance depending on the reservoir’s intended use (source of drinking water, electrical energy generation, flow regulation) and its particularities: shape and mean depth, reten- tion time, surface area of flooded lands, density and nature of vegetation flooded, as well as length of impoundment period (Baxter and Glaude, 1980). Without a doubt the most spectacular and complex changes, from both physical and biological standpoints, are brought about by the creation of a reservoir on a river. Such a reservoir entails permanent transformations to ecosystems, as vast tracts of lands are flooded and river stretches are turned into lakes. A lake can also be transformed into a reservoir by regulating its flow. In such cases, the transformations to ecosystems are less extensive and, in some instances, only tempo- rary. The following section examines major modifications to lake trout ecosystems brought about by the creation and management of reservoirs located on the Precambrian Shield. Water quality The first phenomenon to occur as a result of reservoir impoundment is the leaching of flooded soil and vegetation (Baxter and Glaude, 1980). Mineral salts and nutrients present in the soil are released in the water, aided by the wave action of the rising water shredding the forest floor. While decomposition has yet to begin in the first stages of impoundment, these initial phenomena appear responsible for the sharp rise in total phosphorus and drop in pH (Figure 5.2) (Chartrand et al., 1994). The decomposition of flooded organic matter then follows. This phenomenon leads to consumption of dissolved oxygen, mainly in the deeper strata of the reservoir, lower pH, and release of CO 2 , CH 4 , and nutrients such as phosphorus (Figure 5.2). The low oxygen levels and change in the chemical conditions of deep-zone waters are factors likely to limit the habitat of young lake trout, increase the threat of predation by adults, and ultimately reduce recruitment to the population. However, overall water quality within the reservoir is barely influenced by these benthic processes. Because the volume of water rich in decomposition by-products near the bottom is very small relative to the total volume of the reservoir, the concentrations of these products throughout the reservoir remain low following spring overturn. All of these changes are temporary and subside as time passes (Baxter and Glaude, 1980). For example, in the Robert-Bourassa and Opinaca reservoirs (Québec) as a whole (Chartrand et al., 1994), physicochemical variations peaked quickly (1 to 4 years) following impoundment (Figure 5.2). Modifications related to the decomposition of flooded organic matter were nearly over 9 to 10 years after impoundment. With respect to the Caniapiscau reservoir, Québec (Chartrand et al., 1994), the modifications measured were of the same magnitude as those measured in other reservoirs; however, the maxima for total phosphorus and silica were reached later, between the 6th and 10th year of impoundment (Figure 5.2). In this particular instance, the return to values representative of natural environments was completed 14 years later. It appears that because impound- ment occurred more gradually, over a period of 3 years rather than 6 to 12 months as with the others, the period required for the return of initial conditions was extended. The modification period is brief largely because only a small portion of the flooded organic matter composing the forest soil and vegetation decomposes easily and rapidly. Only the leaves of trees and bushes, conifer needles, forest ground cover, and the first few centimeters of humus decompose rapidly. Most of the other flooded material (tree © 2004 by CRC Press LLC branches, trunks and roots, and deep soil humus) proves to be difficult to decompose and remains really intact dozens of years after impoundment. Mercury is a widespread contaminant in freshwater fish. Lake trout frequently have high concentrations of mercury because of their position at the top of the food chain and because the Boreal lakes that they inhabit often have conditions favorable for mercury bioaccumulation (Bodaly and Kidd, Chapter 9, this volume). Several studies have demonstrated that impoundment brings about a rapid increase in fish mercury levels (Schetagne et al., 1997). The extent of the increase in bioavailability of mercury for aquatic wildlife in reservoirs depends on many factors: the land area flooded, filling time, water residence time, volume of water, proportion of flooded land in shallow environment (where biotransfer is at its maximum), water quality, food web of the flooded environment, fish population dynamics, etc. (Jones et al., 1986; Brouard et al., 1990; Doyon et al., 1996). Research conducted at the La Grande complex (Québec) (Schetagne et al., 1997) showed that depending on the fish species and reservoir considered, maximum mercury concentrations were 3 to 7 times higher than those measured in natural environments. In nonpiscivorous species, mercury levels stop increasing significantly 4 to 5 years after impoundment, and the return to concentrations representative of natural environments is well under way 10 to 15 years after flooding. In piscivorous species, maximum values were attained later than for nonpiscivorous species. Maximum concentrations for walleye Figure 5.2 Variation of principal water quality variables before, during, and after impoundment in the major reservoirs of the La Grande complex (⎯ Robert-Bourassa, … Opinaca, Caniapiscau). (From Chartrand et al , 1994, Commission Internationale des Grands Barrages, Dix-huitième Con- grès des Grands Barrages, Durban, Q.69-R-14, pp. 165-190.) Dissolved oxygen (% saturation) 77 80 83 86 89 92 95 98 101 -2-11234567891011121314 Age of reservoir (in years) (%) Impoundment Silica 0 0,4 0,8 1,2 1,6 2 2,4 2,8 -2-11234567891011121314 Age of reservoir (in years) (mg of SiO 2 /L) Impoundment Total phosphorus 4 6 8 10 12 14 16 18 20 22 -2 -1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Age of reservoir (in years) (µgofP/L) Impoundment pH 5,8 5,9 6,0 6,1 6,2 6,3 6,4 6,5 6,6 6,7 6,8 -2 -1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Age of reservoir (in years) (units) Impoundment © 2004 by CRC Press LLC Stizostedion vitreum, northern pike Esox lucius, and lake trout were reached between 9 and 13 years after impoundment, depending on the reservoir and species. A gradual decrease in fish mercury levels is observed once mercury release activities, including decomposition of flooded organic matter, as well as the erosion and resuspen- sion of flooded organic matter along banks exposed to wave action have declined. Sub- sequently, this erosion of organic matter helps accelerate the decrease in fish mercury levels by reducing the area of shallow zones in reservoirs that still have organic matter available. It is in these shallow zones rich in organic matter where most biotransfer occurs (Shetagne et al., 1997). In the majority of reservoirs, a significant decrease begins to be apparent, for all these species, 14 to 15 years after reservoir creation. The data collected at the La Grande complex, as well as in other reservoirs located in the Precambrian Shield, show that fish mercury levels in reservoirs return to values similar to those measured in natural environments after a period that may range from 15 to 25 years for nonpiscivorous species and from 20 to 30 years for piscivorous species (Shetagne et al., 1997) Water impoundment also affects other aspects of water quality and because the changes result from major alterations in the reservoir’s shape and management, they are permanent. For example, the creation of a reservoir on a river enables the particles that were suspended in the river’s running waters to settle to the bottom more easily. This sedimentation process reduces turbidity and increases light penetration into the water (Chartrand et al., 1994). Plankton A rise in nutrients, particularly phosphorus, which generally limits phytoplankton pro- duction on the Precambrian Shield, can cause an increase in phytoplankton quantity. Phytoplankton abundance had increased by five times in Lake Minnewanka, Alberta 3 years after its level had been raised (Cuerrier, 1954) and had returned to initial levels 8 years later. The rise in nutrients noted in all reservoirs at the La Grande complex (Char- trand et al., 1994), particularly phosphorus, resulted in a threefold increase in chlorophyll a concentration (Figure 5.3). At the Robert-Bourassa and Opinaca reservoirs, maximum concentration was reached 3 to 5 years after impoundment. Once easily decomposed organic matter was depleted, nutrient levels dropped to initial levels and chlorophyll a concentration returned to values similar to those prevailing before impoundment. The return to initial values occurred 9 and 10 years, respectively, after impoundment of those reservoirs. At the Caniapiscau reservoir, maximum values were attained some 10 years after impoundment, and the return to initial values was nearly completed after 14 years. Zooplankton abundance and biomass in reservoirs are influenced by water enrichment and availability of organic matter, produced by flooded vegetation and forest soils, as well as increased retention time. At the Robert-Bourassa reservoir (Chartrand, 1994), zooplank- ton density and biomass reached maximum values in the fourth summer after impound- ment and dropped off slowly afterwards (Figure 5.3). The maximum values were attained a year after chlorophyll a (phytoplankton biomass) (Figure 5.3) and phosphorus concen- trations had peaked (Figure 5.2). Benthos Benthic organisms are divided into several groups according to the way they feed: some filter the water for suspended particles, some grind organic waste such as leaves falling to the bottom of the water, and some prey on other small organisms dwelling on the bottom. Benthic organisms must adapt to the great physical transformations caused by © 2004 by CRC Press LLC the reservoir creations, most notably the flooding of forest and the formation of huge lakes from rivers. After the initial decrease in benthos abundance and change in their composition following the water level rise in lake Minnewanka (Cuerrier, 1954), benthos increased in Figure 5.3 Chlorophyll a variation in the major reservoirs of the la Grande complex (— Robert- Bourassa, … Opinaca, Caniapiscau) and evolution of zooplankton and benthic organisms biomass at Robert-Bourassa reservoir following impoundment. (From Chartrand et al , 1994, Commission Internationale des Grands Barrages, Dix-huitième Congrès des Grands Barrages, Durban, Q.69-R- 14, pp. 165-190.) Chlorophyll a 0,6 1,0 1,4 1,8 2,2 2,6 3,0 3,4 3,8 -2-11234567891011121314 Age of Reservoir (in years) (µg/L) Biomass of Zooplankton -5 0 5 10 15 20 25 30 35 40 45 50 55 -1123456 Age of Reservoir (in years) (mg/m) Cladocerans Calanoids Cyclopoids Rotifers Nauplii Total Biomass of Benthic Organism (Annual Means) 0,00 0,15 0,30 0,45 0,60 0,75 0,90 1,05 1,20 -1 1 2 3 Age of Reservoir (in years) dg/Rock Basket 3,80 Impoundment Control Lake Others: Reservoir Stations © 2004 by CRC Press LLC abundance over the next 10 years, showing adaptation to new conditions. However, the littoral zone, which is subjected to drawdown 5 months per year, is not productive. Significant variations in water level hinder the growth of vegetation in the riparian zone and consequently limit the abundance of benthic fauna. In the reservoirs of the La Grande complex (Chartrand et al., 1994) benthos diversity decreased, mainly in the first years. While species with poor mobility or adapted to running water became scarce, those with greater mobility or requiring little dissolved oxygen rapidly took over the new aquatic habitats. The great number of anchoring points offered by the flooded vegetation increased the surface area of feeding grounds, leading as a result to measurements of greater benthos densities and biomass than in natural lakes (Figure 5.3). Analysis of the stomach contents of reservoir fish and monitoring of fish populations revealed that benthos diversity and quantity were sufficient to sustain major increases in growth rate and condition factors of fish feeding on benthos. These fish included lake whitefish (Coregonus clupeaformis), and their predators, such as the northern pike (Esox lucius). Fish abundance It is known that fish populations are often numerous in the first years of a reservoir's existence (Ellis, 1941, in Baxter and Glaude, 1980). In some cases, reservoir creation can also help increase the fisheries resources of a region (Baxter and Glaude, 1980). The rapid increase in abundance of certain fish species often observed in new reservoirs may have occurred for a number of reasons. Among these could be increased reproduction rate brought about by secure spawning grounds and protection of fry afforded by flooded vegetation. Increased food availability is another. At the time the La Grande complex reservoirs were impounded (DesLandes et al., 1995), overall abundance for all species dropped significantly but then rose over the next 3 years before decreasing slightly up to the 10th year. The drop noted in the first year could have been related to rising water levels and the dilution effect this entails. The subsequent increase in abundance varied in range and duration depending on the species. While abundance of species such as the northern pike and lake whitefish greatly increased, the abundance of longnose sucker Catostomus catostomus, white sucker Catostomus com- mersoni, walleye, and cisco Coregonus artedi, declined sharply following the initial increase. The northern pike is a species that generally does well in reservoirs. In the first years of a reservoir’s creation, its abundance and growth usually increase (Machniak, 1975). When the La Grande 2 (DesLandes et al., 1995) and Caniapiscau (Belzile et al., 2000) reservoirs were created, the relative abundance of northern pike rose sharply and remained steady up to 10 and 17 years, respectively, following impoundment. Although few data are available on lake trout response to the trophic pulse following reservoir creation, the ecosystem changes do not seem favorable to lake trout (DesLandes et al., 1995). Lake trout populations are generally low in Québec’s reservoirs despite the fact that reservoirs present abiotic and biotic factors considered very good for the species (Lacasse and Gilbert, 1992; Gendron and Bélanger, 1993). Québec’s reservoirs containing lake trout populations tend to have much larger surface area than most natural lake trout lakes in the region (Table 5.1). This pattern is also reflected to a lesser extent in the mean and maximum depth. The physicochemical properties of many of the reservoirs on the Pre- cambrian Shield provide good life-sustaining conditions for lake trout populations: near- neutral pH, high concentration of dissolved oxygen, and cold temperatures (Table 5.1) (Gendron and Bélanger, 1993; Benoît et al., 1997). However, adverse effects on fish popu- © 2004 by CRC Press LLC lations spawning in shallow waters can occur if reservoir drawdown exposes spawning grounds during egg incubation or larva development. In Québec, generally speaking, the most abundant lake trout populations are found in deep (maximum depth >30 m), small area (<1,500 ha) reservoirs with an annual draw- down below 1.6 m (except for the Mitis reservoir: 3.0 m). Conversely, populations are less abundant in large upstream reservoirs (>25,000 ha) with strong annual and interannual drawdowns (7.8 m), where impoundment resulted in a sharp rise in water level (Gendron and Bélanger, 1993). However, even though the habitat appears suited to the species and drawdowns are relatively low, in reservoirs created from rivers, lake trout populations are scarce. More recent and specific studies of five Québec reservoirs harboring lake trout pop- ulations (Benoît et al., 1997; Doyon, 1997) revealed that the populations in four of the five reservoirs had been decimated and exhibited significant recruitment problems, most likely in response to drawdown effects. Climatic warming and reservoirs Another concern about the creation of reservoirs is their release of carbon dioxide (CO 2 ) and methane (CH 4 ), both greenhouse gases, into the atmosphere. As we saw previously in this chapter, these gases are the major end products of the microbial decomposition of flooded organic material. Studies of CO 2 and CH 4 fluxes from existing reservoirs (Duchemin et al., 1995; Kelly et al., 1997) have demonstrated that reservoirs are sources of these gases to the atmosphere. However, the net effect of reservoir creation relative to other electric generation options (more specifically: gas, oil, coal), in terms of greenhouse gas production, is controversial. Moreover, predictions of a warmer and drier climate resulting from greenhouse gas accumulation might shift the balance between evaporation and precipitation, which in turn will lead to overall declines in both river flows and lake levels (Magnuson et al., 1997). Under this scenario, reductions in runoff will negatively impact hydroelectric power generation, thus creating a demand for new dams. Building reservoirs in Precambrian Shield would flood more wetlands and terrestrial soils, thus further contributing to cli- matic warming by increasing greenhouse gas fluxes to the atmosphere. Finally, potential impacts of climate warming on reservoirs are reductions in nutrient loading and recycling for many lakes on the Precambrian Shield (Schindler and Gunn, Table 5.1 Characteristics of Québec's Natural Lakes and Reservoirs having a Lake Trout Population Parameters Natural lakes Reservoirs Surface area (ha) 766 ± 7332 28421 ± 73187 N = 906 N = 67 Mean depth (m) 14.1 ± 8.6 22.2 ± 14.5 N = 171 N = 35 Maximum depth (m) 36.7 ± 26.1 64.4 ± 54.6 N = 359 N = 45 Secchi disk transparency (m) 5.2 ± 1.9 5.7 ± 2.9 N = 283 N = 14 Conductivity (µS/cm at 25°C) 46.8 ± 56.7 33.0 ± 31.8 N = 337 N = 11 pH 6.64 ± 0.71 6.63 ± 0.60 N = 379 N = 38 Note: Mean ± SD; N: number of lakes or reservoirs © 2004 by CRC Press LLC Chapter 8, this volume). The change of thermal regime would also cause shrinkage of summer habitats for cold-water fish species such as lake trout. Impacts of reservoirs use on lake trout reproduction The following first examines the impacts on lake trout reproduction by raising the water level during reservoir impoundment. Second, it reviews possible effects of various water level man- agement practices on the quality of reproduction sites and on egg and fry mortality. Characteristics of reproduction sites The lake trout is a fish that reproduces almost exclusively in lakes, although reproductive activities have been documented in the rivers of Ontario and Québec (Loftus, 1958; Vincent and De Serres, 1963; Séguin and Roussell, 1970). The spawning period varies with the latitude. For the Precambrian Shield, this usually means that it takes place in October. Incubation extends over a period of 4 to 5 months, depending on water temperature (Martin and Olver, 1980). The great majority of eggs hatch around March 1, but hatching may occur as early as the end of January or as late as the beginning of April (Chabot and Archambault, 1981; Pariseau, 1981). Lake trout embryos can move extensively within and above the substrate immediately after hatching (Baird and Krueger, 2000). After their yolk sac is fully resorbed, approximately 2 months after hatching, it appears that the young fish immediately migrate to deep waters (Martin and Olver, 1980). To date, it has been impossible to determine whether lake trout return to their birth- place to reproduce. However, it is clear that specific sites are used by spawning stock, sometimes year after year (Gunn, 1995). Lake trout spawning grounds in Québec’s Mau- ricie region are generally located near the shore at a depth of less than 2 m. The substrate is composed mainly (>90%) of cobbles and boulders (40 to 500 mm) without sand or silt, and with numerous and deep interstices. The sites are subject to strong wave action, have a relatively steep slope (>20%), and are located near a deep zone (>30 m) (Benoît et al., 1999). These characteristics are similar to those of many lake trout spawning grounds observed in Ontario (MacLean et al., 1990). For the lake trout, spawning in very deep zones appears more of an exception than the rule because in Ontario lakes (excluding the Great Lakes), 98% of the spawning grounds are less than 4.5 m deep. The average overall depth is 1.4 m (MacLean et al., 1990). The reason for this is that the occurrence of coarse substrate decrease with depth (Chabot and Archambault, 1981). As a result, most of the substrate at depths of greater than 3 to 5 m generally consists of fine particles (sand and silt). However, some spawning grounds at depths below 5 m have been reported (Machniak, 1975). Spawning depth seems to result from a compromise between the forces needed to keep the substrate clear of fine particles and the forces that can cause egg disturbance or mortality. A significant relationship between spawning depth and lake size was obtained using data from 24 lakes (Fitzsimons, 1994) (Figure 5.4): Depth (m) = 0.07 + 0.93 log surface area (km 2 ) (R 2 = 0.79) Effects of raised water level Few studies have focused on the lake trout’s reproductive behavior following reservoir creation, but raising the water level appears to have less of an impact than lowering the level in winter. © 2004 by CRC Press LLC At the Minnewanka reservoir, Cuerrier (1954) observed spawning as usual at tradi- tional sites that had maintained a suitable spawning substrate despite the raising of the water level by 23 m. However, spawning took place over a wider vertical range than before construction of the dam because the lake trout were able to use new rocky areas down to a depth of about 9.5 m. On the contrary, when the water level in Bark Lake, Ontario was raised 11 m in the late 1930s, the lake trout stopped using traditional sites (Wilton, 1985). Inventories carried out from 1966 to 1972 revealed that the lake trout spawned at depths of less than 3 m during that period. Whether it is in terms of substrate or depth, the characteristics of reproduction sites found in reservoirs (Lacasse and Gilbert, 1992; Bélanger and Gendron, 1993; Martin, 1955) are similar to those of sites in natural environments (Dumont et al., 1982). When the water level is raised, fine particles eventually cover traditional reproduction sites (P.G. Sly, personal communication in Evans et al., 1991), rendering them less attractive to breeders because of reduced substrate permeability and cleanliness. However, wave action can clear substrate, presenting characteristics favorable to reproduction and hence creating new sites in shallow areas. McAughey and Gunn (1995) demonstrated that the species was clearly capable of seeking alternative spawning sites when traditional ones were destroyed. Hence, the lake trout will readily abandon traditional reproduction sites and select new, more favorable ones in the vicinity. Effects of water level fluctuations Management of artificial bodies of water designed for hydroelectric production purposes usually requires that the reservoir be filled when water inputs are high and emptied gradually during periods of heavy energy demand. On the Precambrian Shield, three major steps are involved in dam management. The first step, characterized by a rather stable but high water level, covers the summer season (May to August included). The second step, known as drainage, sometimes begins after a slight fall high water stage and lasts until spring thaw. This step makes it possible to supply power plants throughout the winter when energy demand is heavy and water inputs are low. It rests nearly entirely on water loads accumulated during the previous spring thaw or drawn from groundwater tables. Winter drawdowns (October to April) are typical of this step. In the third and last step the reservoir, fed by the spring thaw, fills again at a rapid and constant pace. Figure 5.5 shows typical water level fluctuations in a reservoir used for hydroelectric production purposes. A similar management pattern is observed in reservoirs used to regulate spring flooding. Figure 5.4 Relation between lake size (km 2 , log 10 scale) and lake trout spawning depth (m). (From Fitzsimons, J.D., 1994, Canadian Technical Report of Fisheries Aquatic Sciences, No. 1962.) 0,0 2,0 4,0 6,0 -1,0 0,0 1,0 2,0 3,0 4,0 5,0 Log lake size (km 2 ) Spawning depth (m) [...]... Ministry of Natural Resources districts of Ontario (Lewis et al., 1990) determined the pattern and importance of drawdowns in 85 lake trout lakes A large number (50 ) of these lakes had drawdowns occurring after lake trout spawning Drawdowns occurred before lake spawning on 39 lakes and during spawning on 14 lakes (some lakes had drawdowns occurring at more than one time) The modal drawdown depth was... Congrès des Grands Barrages, Durban, Q.69-R-14, pp 16 5- 1 90 Cuerrier, J.-P., 1 954 , The history of Lake Minnewanka with reference to the reaction of lake trout to artificial changes in environment, Canadian Fish Culturist 15: 1-9 Cohen, Y and Radomski, P., 1993, Water level regulations and fisheries in Rainy Lake and the Namakan reservoir, Canadian Journal of Fisheries and Aquatic Sciences 50 :193 4-1 9 45 DeRoche,... prey species, may have important effects on lake trout For lake trout, change from piscivorous feeding to plankton feeding could result in a slower growth and maturation at a smaller size Impoundment of Lake Minnewanka did indeed cause a shift in the feeding habits of lake trout (Cuerrier, 1 954 ) Lake trout had practically ceased eating fish and were subsisting mainly on small chironomid larvae Cuerrier... deep-spawning lake trout A possible solution to the reproduction problems in reservoirs with extensive drawdowns is the use of a strain of deep-spawning lake trout Introduction in Wisconsin’s Green Lake (Hacker, 1 957 ) of a strain from a deep-spawning subpopulation from Lake Michigan provides an interesting example In this lake, lake trout spawn at depths of 20 to 30 m on a substrate consisting of anything... such methods are technically feasible even on a large scale, they can be costly depending on the distance of spawning areas from the shore, their size, and depth Obstruction of the spawning areas in the littoral zones of Lake aux Sables using a tarp (Benoît and Legault, 2002) led lake trout to abandon these areas and reproduce in the artificial deep-water spawning areas created near the natural sites This... Gatineau Service de la faune du Québec Rapport 5: 12 7-1 58 Swanson, B.L., 1982, Artificial turf as a substrate for incubating lake trout eggs on reefs in Lake Superior, Progressive Fish-Culturist 44(2):10 9-1 11 Tarandus Associates Ltd., 1988, An Evaluation of Selected Lake Trout Spawning Shoals in Lake of Baies, Ontario Ministry of Natural Resources, Toronto Tikkanen, P., Niva, T., Yrjänä, T., Kuusela,... (Figure 5. 7) As the lake trout reservoirs are drawn down, the water is accumulated in the other reservoirs Water management constraints necessitate that early drawdowns in lake trout reservoirs are compensated by drawdowns in the other reservoirs so that the economic impact of the new water management is negligible As a result, lake trout have access to quality spawning areas that are not dried out during... 1990, Changes in Lake trout growth and abundance after introduction of Cisco into Lake Opeongo, Ontario, Transactions of the American Fisheries Society 119:71 8-7 29 McAughey, S.C and Gunn, J., 19 95, The behavioral response of lake trout to a loss of traditional spawning sites, Journal of Great Lakes Research 21(Suppl 1):37 5- 3 83 Pariseau, R., 1981, Inspection d’hiver de la frayère à touladi du lac David... et Aménagement du Territoire, vice-présidence Environnement, Hydro-Québec Gunn, J.M., 19 95, Spawning behavior of lake trout: effects on colonization ability, Journal of Great Lakes Research 21(Suppl 1):32 3-3 29 Hacker, V .A. , 1 957 , Biology and management of lake trout in Green lake, Wisconsin, Transactions of the American Fisheries Society 86:7 1-8 3 Haxton, T., 1991, Lake trout spawning shoal rehabilitation... shoreline out of water and enabling a greater proportion of lake trout eggs to survive winter drawdown Reasons for the interannual fluctuation include major water input in winter and low demand for electricity Lake trout eggs may hatch towards the end of winter or in early spring, usually between February and April depending on developmental conditions The fry move about very little and remain hidden among . spawning areas in the littoral zones of Lake aux Sables using a tarp (Benoît and Legault, 2002) led lake trout to abandon these areas and reproduce in the artificial deep-water spawning areas. Wisconsin’s Green Lake (Hacker, 1 957 ) of a strain from a deep-spawning subpopulation from Lake Michigan provides an interesting example. In this lake, lake trout spawn at depths of 20 to 30 m on a. Ontario (Lewis et al., 1990) determined the pattern and importance of drawdowns in 85 lake trout lakes. A large number (50 ) of these lakes had drawdowns occurring after lake trout spawning. Draw- downs