Browsing by Author "Zymonas, Nikolas Dainus"

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Age structure, growth, and factors affecting relative abundance of life history forms of bull trout in the Clark Fork River drainage, Montana and Idaho
(Montana State University - Bozeman, College of Letters & Science, 2006) Zymonas, Nikolas Dainus; Chairperson, Graduate Committee: Thomas E. McMahon
Bull trout Salvelinus confluentus exhibit high variability in life history patterns. Better understanding of the underlying mechanisms is needed to assist conservation efforts. I assessed relationships among life history form, growth rates, age structures, and environmental variables, using pelvic fin rays and scales to estimate age and growth. First, I assessed the effects of pelvic fin ray excision on survival and growth of age-3 and age-4 bull trout. Survival and growth were similar between fin ray-excised and control fish within each age group, although a bacterial coldwater disease infection caused higher mortality in age-3 fish. Excised rays achieved a mean 42% regeneration by six months. Second, I developed methodology for using pelvic fin rays to estimate age and growth. Suitability of fin ray sections was based on overall morphology, appearance of early annuli, and presence of a conspicuous dash in the nucleus. Back-calculation for juvenile and non-migratory bull trout produced real error (mean ± SE) of 4.1 ± 2.0% and absolute error of 7.2 ± 1.2% of known lengths one year prior. Ageing precision and accuracy of growth estimates using fin rays compared favorably to those from scales.