Limnobiology of Cowichan Lake, British Columbia

Abstract

Cowichan Lake is 34 kilometres long, up to 4 kilometres wide and up to 150 metres deep, with an area of 62 square kilometres. Its average depth is 51 metres. Its shores are of precipitous rock for over half their length, the remainder being boulders or gravel, with a very little marsh.Summer surface temperatures are usually close to 20 °C., while the winter minimum in 1938 was 5.0°. Oxygen is generally abundant in the lake, the lowest value observed being 3.4 cc. per litre, just before the fall overturn (November 24, 1939). The reaction of the water is alkaline (pH 7.0–7.8), and its bicarbonate content was 18–22 mg. per litre (as CaCO3).Lists are presented of organisms collected in the lake. The plankton is reasonably rich in variety but was poor in quantity, in 1940 at least. Bottom organisms also are not abundant. Two species of lampreys and three fishes were found in the lake, plus a number of Salmonidae whose occurrence is described elsewhere.

GEOGRAPHIC VARIATION AND ENVIRONMENTAL SELECTION IN GASTEROSTEUS ACULEATUS L. IN THE PACIFIC NORTHWEST, AMERICA

“…1940Hartley. ,1948Hynes, 1950;Carl, 1953), and those in streams on benthic organisms ( Hartley, 1940( Hartley, , 1948Markley, 1940;Hynes, 1950;Maitland, 1965;Hagen, 1967). Stream populations of sticklebacks colonizing large lakes may well be subject to strong selection for increased numbers of rakers, with consequent convergence on trachurus.…”

The feeding relationships of brown trout, minnow and three-spined stickleback in an upland reservoir system

“…Most authors agree that stickleback feed mainly on zooplankton (Norman, 1936Ƚ Hynes, 1950Ƚ Carl, 1953Ƚ Greenbank & Nelson, 1959Ƚ Ƚllen & Wootton, 1984 . Ƚt Roundwood the diet of the stickleback was also dominated by zooplankton although insects which occurred on the surface or passing through the water body were also taken .…”

Occurrence of a thermocline in two lakes of the semi-arid region in western Rajasthan, India

“…Ganapati's (1960) report of the occurrence of thermal stratification in tropical lakes and ponds is based on the observations of a few days only and is insufficient to give a clear picture of thermocline formation and what Sreenivasan (1964cSreenivasan ( , 1971Sreenivasan ( , 1976 reported an epilimnional thermal stratification in the Yercaud lake and diurnal thermal stratification in Pillar reservoir and Sarvatheertham temple pond in South India, are only ill defined thermoclines with a maximum difference of 3 .3°C only between the surface and the bottom layers . However, in temperate countries quite a large number of cases have been reported about the occurrence of thermoclines in deep water lakes (Ruttner, 1931 ;Carl, 1953 ;Melony et al, 1969 ;Zyblut, 1970 ;Fish, 1970 andAlexander &Barsdate, 1971) as well as in shallow ponds or lakes (Pennak, 1949 ;Wright, 1954Ramsey, 1960Winner et al, 1962 andGreen, 1974) . Green (1974) also mentioned that this thermocline development was usually attributed to `small surface area coupled with sheltered conditions' .…”