The available data on the fish populations of 35 lakes in the Northwest Territories are examined. The lakes range in size from Great Bear Lake (31, 156 km2) to Keyhole Lake (46 ha); they are situated between lat. 60 and 75° N, east from the Mackenzie River to the west coast of Hudson Bay. Lake trout (Salvelinus namaycush) and whitefish (Coregonus clupeaformis) form the main populations of the mainland lakes and together make up to 95% of the total catch. There is a trend toward increasing importance of whitefish with decreasing severity of conditions. Most populations show a uni, bi-, or trimodal length distribution; age distributions are unimodal. No change in these distributions was observed over a large number of years in certain lakes. These populations are considered to have reached a climax condition comparable with a vegetational climax, and are therefore in equilibrium with their environment. All incoming energy is ultimately used in respiration to support a high biomass of fish.
Land-locked populations of Arctic charr in four lakes on Northern Ellesmere Island (80" N) were found to consist of two distinct sizes: ' dwarf' and ' normal ' charr. Both groups attained sexual maturity but differed in appearance and habitat. The smaller fish, occupying the more marginal habitats, retained their parr-markings; the larger group had the general characteristics of smolts, being more silvery and without parr-marks. In their juvenile stages, the charr destined to attain the larger group were indistinguishable from members of the smaller group. Although fish in the larger group were capable of cannibalism, this was rarely observed. In general, the fish in the larger group were older than the smaller ones but great variation in size at a given age resulted in certain age classes containing representatives of both groups. The population structure varied considerably between lakes; a high proportion of ' normal ' charr correlated well with a high growth rate in the first few years of development. It is postulated that the two groups live in dynamic equilibrium where the advantages of progenesis (retention of juvenile characters by adults) in the smaller type are traded against the larger proportion of the energy resources available to the larger type. The concept of heterochrony in an ecological setting is introduced.
Benthic invertebrates in Great Bear Lake are most highly concentrated in the upper 20 m. Densities between 20 and 100 m are low; below 100 m only Mysis relicta and Myoxocephalus quadricornis exist at measurable densities. All benthic organisms exhibit a high degree of patchiness.Lake trout, Salvelinus namaycush, and M. quadricornis are two species that inhabit the lake at all depths (3–400 m) and temperatures (13.2 C for M. quadricornis and 15 C for S. namaycush).Whitefish, Coregonus clupeaformis, inhabit only the bays, seldom being caught in water over 20 m deep. The distribution of whitefish is considered to be restricted mainly by the density of benthic organisms.Three species are confined to the periphery of the lake, Stizostedion vitreum, Lota lota, and Catostomus catostomus. Two species, Couesius plumbeus and Percopsis omiscomaycus, are present in the headwaters and Great Bear River but have not been able to establish themselves in Great Bear Lake. Extreme oligotrophy is considered to have had the effect of reducing species diversity.
Freshwater Institute, Department of Fisheries and Oceans, 501 University Crescent, Winnipeg, Man. R3T 2N6 JOHNSON, L. 1983. Homeostatic characteristics of single species fish stocks in Arctic Bakes.Can. J. Fish. Aquat. Sci. 40: 987-1024.The results of investigations on the fish stocks of seven Arctic lakes covering a period of 23 yr are described. These lakes have remained largely undisturbed since their formation in late glacial times; all but one are completely autonomous and of comparatively small size. Such lakes provide a unique opportunity for the development and testing of conceptual models. In all cases the only fish species present is Arctic cham, Salvelinus alpinus. Length frequency distributions derived from gfllnet catch curves are shown to be, within reasonable limits, representative of the actual populations in the lake, and not artifacts of the sampling procedure, Length frequency curves show a unimodal or bimodal distribution and this structure, in the absence of perturbation, appears to remain constant indefinitely. Individuals are of great age but age-at-length is highly variable. Age and size structure are shown to be comparable with the age and size structure of the dominant tree species in a climax forest; it is concluded that forces of great generality fashion these configurations. It is hypothesized that all species tend to move towards a state of least energy dissipation; this can be most readily seen in the dominant species at the climax in an autonomous system. The dominant species is characterized by large individual size, a high degree of uniformity, high total biomass, great mean age, indeterminate age-at-death, and a low incidence of replacement stock. After severe perturbation it is shown that the c h m stock returns to a state of least dissipation without oscillation. Absence of oscillation during the return to the initial state, combined with the long-term stability shown in control lakes, indicates the presence ~f an effective damping mechanism; this in turn indicates the existence of organization within the stock as a whole. Organization develops through an interactive mechanism described under the doctrine of homeokinesis, which is responsible for energy equipartitioning and the maintenance of uniformity. These concepts help to explain phenomena observed in more complex systems and help our understanding of ecosystem functioning. JOHNSON, L. 1983. Homeostatic characteristics of single species fish stocks in Arctic lakes.Can. J. Fish. Aquat. Sci. 40: 987-1024.form. "'Char Lake" referred to later in the text is a statutory name not to be interfered with except by due process of law.
Eight sexually mature sockeye (Oncorhynchus nerka) and one sexually mature pink salmon (O. gorbuscha) were captured in the subsistence fishery in the Sachs River estuary at Sachs Harbour, Banks Island, Northwest Territories (NT) in August 1993. We also report a first record for coho salmon (O. kisutch) in Great Bear Lake, NT. These capture locations are well outside the known distributions for the species. A pink salmon captured in the West Channel, Mackenzie River near Aklavik, NT, and a chum salmon (O. keta) from Cache Creek, NT, also represent new capture locations within the distribution of the species.
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