Date of Award

2011

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Natural Resources

First Advisor

Marsden, Ellen

Abstract

Lake whitefish (Coregonus clupeaformis), in the family Salmonidae, is a coldwater species that is widely distributed in North America. Throughout their range, whitefish support one of the most economically valuable freshwater fisheries and were also commercially fished in Lake Champlain. My goals were to quantify seasonal diet, determine temporal and spatial changes in larval abundance, evaluate biological parameters (size and age structure, sex composition, growth, condition, energy density, and fecundity), and determine if the introduction of zebra mussels (Dreissena polymorpha) to Lake Champlain in 1993 had similar affects on the whitefish population as seen in many of the Great Lakes. Whitefish were collected year-round using gillnets and bottom trawls. Diet was quantified seasonally. Temporal and spatial changes in larval abundance were determined by ichthyoplankton net catches. A comparison of scales, fin rays, and otoliths indicated that otoliths provided the lowest bias and highest precision. Age estimation using otoliths generated a wider range of ages and greater number of age classes when compared with scales and fin rays and therefore age and growth were determined using otolith age estimates. Growth parameters of the entire main lake population were estimated using the von Bertalanffy growth model (K = 0.20; L∞ = 598 mm), mean condition using Fulton’s K condition factor (K = 1.05) and by determining energy density, and fecundity using the gonadosomatic index (GSI = 13.9). Larval whitefish were abundant throughout much of the main lake, but absent in Missisquoi Bay and rare in Larabee’s Point, the historic commercially fished locations. Diet varied seasonally; whitefish fed primarily on large numbers of fish eggs in the spring and transitioned to foraging on mysids in the summer and gastropods in the fall and winter. Surprisingly, zebra mussels made up less than 1% of the diet and appeared in less than 10% of the stomachs analyzed, despite being abundant in the benthos. Biological parameters (size and age structure, sex composition, growth, condition, energy density, and fecundity) of whitefish in Lake Champlain were typical of an unexploited population, with multiple length and age classes represented. Condition was high and representative of a diet with high energy content. Whitefish in Lake Champlain had similar high energy density to those in Lake Erie, where declines in whitefish condition were not associated with dreissenid invasions, and had greater mean energy density than whitefish in lakes Michigan, Huron, and Ontario. I concluded that the current whitefish population in the main lake of Lake Champlain is typical of an unexploited population. However, whitefish apparently no longer use Missisquoi Bay and Larabee’s Point for spawning, most likely because of human alteration of habitat conditions. The high condition factor and energy density of whitefish in Lake Champlain, in contrast to the Great Lakes, is probably a result of their ability to attain sufficient energy sources from an intact native forage base.

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