DYNAMICS IN YEAR-CLASS STRENGTH, GROWTH, AND CALCIFIED-STRUCTURE SIZE OF NATIVE LAKE TROUT (SALVELINUS-NAMAYCUSH) EXPOSED TO MODERATE ACIDIFICATION AND WHOLE-LAKE NEUTRALIZATION

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 1 975 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 1 976 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.