Comparison of Saugeye Age Estimates and Population Characteristics Using Otoliths and Dorsal Spines

Saugeye are hatchery produced hybrids (female walleye [Sander vitreus] and male sauger [S. canadensis]) that have been introduced to aquatic systems throughout the United States. The Oklahoma Department of Wildlife Conservation (ODWC) stocks reservoirs throughout Oklahoma with saugeye to control overcrowded, stunted white crappie (Pomoxis annularis) populations and to provide recreational fishing opportunities. Because sacrificing fish regularly to remove otoliths for age estimation is often unpopular with anglers, a non-lethal means of obtaining age estimates for saugeye to describe population dynamics is desirable. Therefore, we compared age estimate precision between readers and structures (otoliths and dorsal spines), and compared age-based population parameters (growth, mortality, recruitment) derived from these age estimates. Structures were removed from 47 saugeye collected from Thunderbird Reservoir, Oklahoma via electro fishing. Separate age-length keys were developed using consensus ages estimated from each structure, and ages were applied to an additional 253 unaged saugeye (300 fish total) for comparison of age-based population parameters for each structure. Precision was highest between readers for broken otoliths (100% agreement; CV = 0%) and whole otoliths (98% agreement; CV = 3.2%), whereas precision was poor for dorsal spine ages (55% agreement; CV = 22.3%). When comparing final consensus ages, broken otoliths and whole otoliths were in 100% agreement; however, otolith and spine agreement was 14%. Age bias plots indicate that final consensus spine ages always were higher than the final consensus ages from otoliths. Because age assignments from the two structures were dissimilar, corresponding mortality rates, growth models, and recruitment patterns were vastly different. We concluded that dorsal spines are not an appropriate aging structure for saugeye in Oklahoma, as age estimates lacked precision and produced erroneous population parameters. Fisheries managers should continue to sacrifice saugeye to obtain otoliths for aging for the most reliable data.

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