Changes in Lake Trout Growth Associated with Mysis relicta Establishment: A Retrospective Analysis Using Otoliths

Abstract

The establishment of the opossum shrimp Mysis relicta in Flathead Lake, Montana, was followed by a dramatic increase in the population of lake trout Salvelinus namaycush. Using otoliths, we compared lake trout growth before and after the arrival of M. relicta. The widths of annual increments 1-3 were similar, but width generally declined in increments 4-10 after the establishment of M. relicta. To calculate body size in the post-M. relicta fish, we used the relationship between body length and otolith radius. To retrospectively calculate body length for the pre-M. relicta fish (for which we lacked body sizes), we developed a simple empirical correction to account for the conservative nature of otolith growth rate relative to body growth rate.