Dynamics in Year-Class Strength, Growth, and Calcified-Structure Size of Native Lake Trout (Salvelinus namaycush) Exposed to Moderate Acidification and Whole-Lake Neutralization

Abstract

Accurate age-interpretation techniques were developed, using scales and otoliths, to examine the role of whole-lake neutralization in the resurgence of a lake trout (Salvelinus namaycush) fishery in Nelson Lake (pH 5.7) near Sudbury, Ontario. Calcified structures and data from 860 lake trout were collected from 1972 to 1987. The population was characterized by the regular cyclic occurrence of strong year classes, which were probably an effect of pulse angling, cyclic food abundance, and possibly intraspecific interaction. The majority (65.8%) of the lake trout caught in the exceptional winter fishery of 1980 (3.3 kg∙ha−1) were in the lake prior to liming in 1975–76. Young lake trout (up to age 4) of the 1975 and 1976 year classes grew bigger and had larger scales than other year classes from 1973 to 1977, coinciding with an increase in hypolimnetic zooplankton, probably related to improved water quality. Otoliths grew significantly larger and more translucent and exceeded relative growth of scales and body for all ages in 1976 (18% greater) and for the 1976 year class, confirming that otolith accretion can come from the ambient water because liming increased the calcium content by 33% that year, the only observed direct effect of the treatment.

Brackish-water residency and semi-anadromy in Arctic lake trout (Salvelinus namaycush) inferred from otolith microchemistry

“…Annuli were identified as dark bands representing decreased winter growth (Casselman and Gunn, 1992). Age estimations that could not be agreed upon by the readers were removed from further analysis.…”

Growth chronologies of white sucker, Catostomus commersoni, and lake trout, Salvelinus namaycush: a comparison among lakes and between trophic levels

“…Methods for lake trout otolith preparation and analysis followed those outlined by Casselman and Gunn (1992). Sagittal otoliths were removed, placed in small tubes, and allowed to dry.…”

“…Growth increments were measured from the nucleus to the maximum ventral radius of the otolith impression. Criteria for annulus demarcation followed those of Casselman and Gunn (1992).…”

Life history differences between fat and lean morphs of lake charr (Salvelinus namaycush) in Great Slave Lake, Northwest Territories, Canada

“…One otolith from each fish was embedded in epoxy, and a thin transverse section (400 lm) was cut, mounted on glass slides, polished, and photographed for age and growth assessment (Hansen et al, 2012). Annuli were counted by three independent readers using criteria described by Casselman & Gunn (1992), and specimens were excluded from analysis if the coefficient of variation (CV) of age estimates was more than 5% (Campana, 2001). Age estimates were used to inform demarcation of growth increments, measured from the nucleus to the maximum ventral radius of the otolith, and radial measurements at each annulus were used to backcalculate length at age using the biological intercept back-calculation model (Campana, 1990).…”