AUTHORS: Amelia Finnell, US Fish & Wildlife Service; Patrick Padilla, US Fish & Wildlife Service; Garrett Johnson, US Fish & Wildlife Service; Benjamin Marcek, US Fish & Wildlife Service
ABSTRACT: Silver Carp Hypophthalmichthys molitrix are invasive to the Mississippi River Basin and may cause extensive economic and ecological damage. To date, managers have focused on using harvest to control Silver Carp populations. Assessment of harvest as a management tool often requires precise age estimates to understand the changes in population age structure in response to harvest. Currently, two methods are commonly used for preparing Silver Carp otoliths for aging, sectioning and sanding. However, the use of two distinct methods could affect the precision of age estimates and, consequently, alter the perceived age structure of the population. To address this, we aged 155 Silver Carp (total length: 545–800mm) collected during 2023 from JT Myers and Newburgh Pools of the Ohio River. One lapilli otolith from each fish was prepared by sanding the otolith down to its origin, whereas the other otolith was sectioned using an isometric saw. Each otolith was independently aged by five readers and the frequency of agreeance was calculated using an empirical cumulative distribution function. Reader agreeance, two readers aging the otolith identically, did not differ between the two methods. However, when readers disagreed, the magnitude of disagreement was greater when otoliths were prepared by sanding relative to sectioning. These results suggest that sectioning otoliths results in more precise Silver Carp age estimates. Therefore, the sectioning method may produce more consistent age structures for Silver Carp populations which will help managers accurately assess the status of populations as well as the effectiveness of management actions.
