Otolith from a 10-year-old lake whitefish. - USFWS photo

During the month of January, Fishery Biologist Scott Koproski finished aging lake whitefish otolith samples collected during the 2004 and 2005 distribution study.  This three-year study is funded through the Great Lakes Fish and Wildlife Restoration Act  and involves the collaboration of seven agencies for the tagging of whitefish at eight Lake Huron main basin sites each year.  The objective of this study is to delineate the spawning stocks of lake whitefish in Lake Huron.  At each location, 1,500-3,000 lake whitefish will have a Floy Tag inserted, will be measured to the nearest millimeter, and scales will be removed for age determination. 

In addition to the tagged fish, 50 male and 50 female lake whitefish will be sacrificed daily for more extensive data collection.  Biological data collection for these 100 fish includes length, weight, lamprey wounding, visceral fat indexing, sex, maturity and removal of age structures (scales, otoliths, and fin rays). 

Koproski used the “crack and burn” technique to identify annuli present within each otolith.  When this technique is used, two distinct growth patterns can be identified: broad summer growth and narrow winter growth.  By counting the bands of winter growth, age estimates can be obtained from the otoliths.  A total of 500 fish were aged using this technique.