Studies on the biology of sexually mature male salmon parr, Salmo salar (Linnaeus) 1758, in insular Newfoundland

Dalley, Edgar L. (1978) Studies on the biology of sexually mature male salmon parr, Salmo salar (Linnaeus) 1758, in insular Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Precocious male Atlantic salmon (Salmo salar) parr were investigated in eastern, central and western areas of insular Newfoundland. The percent precocity varied in different areas, but Placentia Bay samples generally had a higher incidence. The proportions of male parr maturing increased beyond age 1+. Limited evidence indicated that precocity at age 0+ is rare. -- Maturing males were larger than immature males at 1+ in all samples and significantly larger in one sample. Older precocious males were not larger than immature males of the same age indicating that maturity begins earlier in fast growing fish but that growth consequently slows down. Faster growth appeared to be related to precocity within a particular system but this relationship was not especially apparent in comparisons between systems Overlap of 95% confidence intervals placed around eviscerated weights (calculated from regression equations) at corresponding lengths indicated no difference between weights for mature and immature parr. However the length-weight relationship was lower for precocious (spent) smolt than for immature smolt in larger length classes. -- Sex ratios of each age group of the samples were often found to differ significantly from 1:1. Possible causes for these deviations are discussed in terms of sex-related distribution patterns and mortality of precocious parr. Evidence is presented from certain sex ratios and from a tagging program that precocious males move upstream to spawn and circumstantial evidence indicates that they spawn with adult females. -- Sex ratios in freshwater following the smolt run and of the smolt run indicates that most precocious parr do not migrate as smolts. The younger parr (1+ and 2+) may mature again while it appears most 3+ and older parr have a high mortality. -- Existing data indicate that rivers with a high percentage of sexually precocious males have a corresponding high percentage of adult females, most likely as a result of few male smolt.

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