**The title, authors, and abstract for this completion report are provided below.  For a copy of the completion report, please contact the GLFC via e-mail or via telephone at 734-662-3209**

Proximate body composition and measures of lake trout lipid content

Mara S. Zimmerman^2,3 and Charles C. Krueger²

² Great Lakes Fishery Commission, Ann Arbor, MI 48105

³ Michigan State University, East Lansing, MI 48824

August 2009

ABSTRACT:

Lipid content is a defining feature of shallow- versus deep-water lake trout. Efficient methods for assessing lipid content will help evaluate lake trout condition over space and time. This study tested the usefulness of a microwave energy meter for measuring lipid content in lake trout. Objectives were to (i) identify lake trout morphotypes from two regions in Lake Superior, (ii) describe body composition of morphological groups, (iii) determine the relationship between lipid content, energy meter readings, and buoyancy of lake trout, and (iv) evaluate sample sizes needed to detect lipid differences. Lake trout collected from two geographically distinct regions of Lake Superior represented four different morphological groups (Objective i) and ranged from a lean to siscowet body shape. Morphological groups differed in lipid content (Objective ii); average lipid content ranged between 9.1% and 22.2% in the Big Reef region and between 2.0% and 10.7% in the Isle Royale region. Microwave energy meter and buoyancy measures were both correlated with lake trout lipid content (Objective iii). Sample sizes needed to detect differences in lipid content will be more strongly impacted by the magnitude of difference between groups than the measurement method (Objective iv). Use of the energy meter, which allows processed fish to be released, may be particularly beneficial if lethal samples are a conservation concern or if study objectives require multiple measures from a single fish over time.