Stock assessments and biological investigations of kokanee (Oncorhynchus nerka) in Cowichan Lake, British Columbia, 1984-1987 / by D.T. Rutherford, C.C. Wood, and J.R. Candy.: Fs97-4/1995E-PDF

"Cowichan Lake has a maximum depth of 160 m and surface area of 6360 ha. Annual hydroacoustic and trawl surveys conducted on Cowichan Lake from 1984 to 1987 indicated a kokanee population of 3.4 to 5.1 million fish (mostly juveniles) with densities ranging from 540-822 fish/ha. Kokanee were far more numerous than any other fish species in the limnetic zone. They matured at age 3 at lengths ranging from 153 to 172 mm. Males were more numerous than females in all five samples of juveniles examined from three consecutive years; the proportion of males ranged from 0.53 to 0.74. A higher proportion of large kokanee (age 1+ and 2+) were caught in seine catches than in midwater trawl catches, which suggests that the two gear types select for different size classes. Age 1+ and 2+ kokanee from Cowichan Lake showed some ability to osmoregulate in salt water; plasma sodium levels varied widely from 172 to 258 mmol/L (mean=197 mmol/L) among 27 fish held for 24 h at a salinity of 23‰. Biochemical genetic comparisons at five polymorphic loci suggest that Cowichan Lake kokanee are more similar genetically to the neighbouring Cheewhat Lake sockeye population than to the other Vancouver Island stocks sampled"--Abstract, page v.

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