Association between emigration and age structure in populations of brook trout (Salvelinus fontinalis) in Adirondack lakes

Abstract

Patterns of emigration by brook trout (Salvelinus fontinalis) from five Adirondack lakes indicated a synchronized, repetitive response to seasonal stimuli over a 13-year period. Emigration occurred in the spring and fall with virtually no movement in the winter and summer. Spring emigration coincided with peak runoff from snowmelt and consisted of small numbers of mostly yearlings (94.8% of emigrants). Large scale fall emigration from four lakes (32.7-68.8% potential losses from populations), by mostly mature fish (94.6% of emigrants), coincided with the spawning season for brook trout. Fall emigrants were likely searching for spawning sites, which were limited or unavailable within the lakes. In a larger set of 14 lakes, the greatest proportion of older (age 3) brook trout occurred in lakes with no outlets, which prevented emigration. In drainage lakes with outlets present, the proportions of older fish in lakes with later maturing strains (age 2-3) were greater than in those with earlier maturing strains (age 1-2). Later age at maturity would have delayed fall emigration from these lakes. Fall emigration appears to be a major factor that causes the virtual absence of older brook trout in many Adirondack lakes and must be assessed in future population dynamic studies.