An Age Comparison Study : Using the Maxilla as an Alternative Age Determination Method for Lake Michigan lake trout, Salvelinus namaycush

Abstract

The understanding of fish population dynamics is essential to conservation efforts and the regulation of fishing individual species. The capture of lake trout (Salvelinus namaycush Walbaum) and the extraction of calcified structures for age determination are necessary to study changes in the species’ populations within the Great Lakes. There are two structures, scales and otoliths, which are widely used for age determination. However, it is well known among fish biologists that scales are largely inaccurate at determining ages in older fish. Studies show that the otolith is the most precise structure for determining age, although it is quite difficult to read and years of experience are required to achieve accurate readings. Recently, a technician in Alpena, MI discovered that thin sections of the maxillary bone, or upper jaw, proved to be much easier to read and just as accurate as the otolith. In this study, I compared ages obtained from scales, otoliths, and maxilla to the true age of the fish from which they were taken, using structures obtained from fish containing coded wire tags (CWTs) and distinct fin clips. Additionally, I created visual comparisons of the accuracy of each structure. I found the maxilla to be a much more accurate structure for age determination in both CWT fish and fin clipped fish. Otoliths were second in accuracy though the reads obtained from them tended to over-age the fish. Scales proved to be accurate only in younger fish. These findings could aid in the improvement of age determination accuracy for more species of fish as well as allow future technicians to age fish with much less training.