UBC Theses and Dissertations
Selective mortality of juvenile sockeye (Oncorhynchus nerka) in Babine Lake determined from body-otolith relationships West, Cameron John
The presence of differential growth and mortality was investigated among juvenile sockeye (Oncorhynchus nerka) in Babine Lake. Emergent fry were collected from the rivers and artificial spawning channels of the Fulton River and Pinkut Creek systems in May and early June of 1979. Juvenile samples were tow-netted from Babine Lake in July, August and September, and smolt samples were collected in May and June of the following year at the outlet of the Babine-Nilkitkwa lake sys tern. Fork lengths and the dimensions of sagitta otoliths were measured. Orthogonal polynomials fitted to Ln fork length versus Ln otolith size between the stages of fry emergence and smolt migration were sigmoid with r² values of 0.97 to 0.98. Significant stock differences were found among linear regressions of Ln fork length versus Ln total otolith length of emergent fry from Fulton River, Pinkut Creek and the three artificial spawning channels. Grouping of Fulton versus Pinkut or of river versus channel sources was not obvious. An average regression was calculated for general use with emergent fry from the main lake population. Instantaneous growth rate of fry in early July was positively correlated with fork length. The distributions of emergent fork length back-calculated from juvenile and smolt samples indicated higher mortality rates among fry with smaller fork lengths at emergence. The timing of the selective mortality was between mid-August and smolt migration in the following spring. The association of smaller initial body size with increased probability of parasitization by the cestode Eubothrium salvelini, subsequent slower growth and the effect on the size distribution of the year class is discussed.
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