An Evaluation of Age Estimation Structures for Lake Whitefish in Lake Michigan: Selecting an Aging Method Based on Precision and a Decision Analysis

摘要

Declines in growth and condition of lake whitefish Coregonus clupeaformis in Lakes Huron and Michigan have led to increased mean age in the harvest and greater difficulty in scale age interpretation. We evaluated the precision and efficiency of scale acetate impressions, transverse pectoral fin ray sections, and transverse sagittal otolith sections for three lake whitefish stocks (Bailey's Harbor, Naubinway, and Saugatuck) that were sampled in Lake Michigan during 2004 and 2005. We conducted a decision matrix analysis that incorporated capital, production, and personnel costs and precision of age estimates to determine the best aging method given current management priorities. For the Bailey's Harbor stock, age estimates were systematically lower based on scales (mean = 7.85 years) than based on fin rays (8.44 years) or otoliths (8.78 years); fin ray and otolith estimates did not differ significantly. Similar results were observed for both Naubinway and Saugatuck stocks. For Bailey's Harbor lake whitefish, greater precision in age estimates was achieved by use of fin rays (median coefficient of variation [CV] = 4.88%) than by use of scales (5.44%) or otoliths (5.44%). For the Saugatuck stock, age estimates were more precise when obtained from pectoral fin rays (median CV = 4.96%) than from scales, but precision did not differ between fin ray and sagittal otolith ages. Differences between scale and pectoral fin ray age estimates began at age 5 for the Bailey's Harbor stock and at age 6 for the Naubinway and Saugatuck stocks. Differences between scale and sagittal otolith age estimates began at age 5 for the Bailey's Harbor and Saugatuck stocks and at age 8 for the Naubinway stock. Based on the decision matrix analysis, pectoral fin rays provided more-precise estimates and their use involved lower costs than use of the other methods; therefore, pectoral fin rays were deemed the best method for aging lake whitefish in Lake Michigan under current conditions.