VARIATION IN MALE PARR MATURATION WITHIN AND AMONG POPULATIONS OF ATLANTIC SALMON, SALMO-SALAR

The covariation of growth and maturation in male Atlantic salmon parr, Salmo salar, produces a relationship characterized by a size threshold below which individuals generally do not mature. The threshold of 70-72 mm fork length is evident both within and among populations. Parr maturation can reduce growth during the second year of life by an average of 4.0%. Among-year variation in growth rate affects the yearly incidence of maturation for males at age 1+ but has no detectable effect on the total proportion of male parr maturing in a population. Increases in the proportion of mature parr in the Matamek River, Quebec [Canada], can be explained by variation in growth alone; there is no evidence for genetic changes in this population.