Cross-section of a Black Crappie sagittae otolith under magnification. This fish collected from Swan Lake was estimated to be 4 years old. - photo by Patty Herman

Colby Wrasse and Patty Herman continued the data collection phase of the Swan Lake Habitat Rehabilitation and Enhancement Project.  Wrasse trained Herman on the "art and science" of age estimation using sagittae otolith bones removed from bluegill, black crappie, white crappie and freshwater drum samples collected in various seasons throughout the last year. 

Thus far, fish have ranged in age from young-of-year to 18 years old.  Otoliths were also digitized using Scion Corporation CFW-1310C model microscope mounted color digital camera.  Photos were then analyzed using Scion Image image analysis software to perform back calculations - a method of estimating sizes at previous stages of growth. 

Swan Lake is a backwater lake located at Two Rivers National Wildlife Refuge in Calhoun County, Illinois.  As part of the HREP, the lake has been divided into compartments where water levels can be individually manipulated. 

By collecting and analyzing fish samples for age and size structure in these compartments and selected reference lakes, preliminary assessments of fish reproduction and recruitment can be made.  These data will ultimately be used in part to determine the effectiveness of periodic draw downs as a management regime to encourage native vegetative growth and improve fish habitat in a controlled backwater site.