AUTHORS: Lydia Flinders, Iowa State University, U.S. Geological Survey, Iowa Cooperative Fish and Wildlife Research Unit; Juliana Kaloczi, Iowa State University, U.S. Geological Survey, Iowa Cooperative Fish and Wildlife Research Unit; Ryan Hupfeld, Iowa Department of Natural Resources; Mark Flammang, Iowa Department of Natural Resources; Rebecca Krogman, Iowa Department of Natural Resources; Michael Moore, Iowa State University, U.S. Geological Survey, Iowa Cooperative Fish and Wildlife Research Unit
ABSTRACT: Sturgeon are a group of long-lived, migratory, and late-maturing fishes that often do not reproduce annually. Globally, these traits make sturgeon species vulnerable to overharvest for caviar, habitat degradation, and fragmentation from dam construction, which can disrupt their reproductive migrations. Larger female sturgeon generally have higher fecundity making them reproductively valuable. To protect the reproductive potential of adults and recover or maintain populations, managers have enacted harvest restrictions for North American species. However, managers lack information on how Shovelnose Sturgeon reproductive capacity varies in different environments. Annual or lifetime reproductive output differs based on body-size fecundity relationships or due to varying size distributions in each population. Stage four, or FIV, is the black egg stage when females are considered reproductively ripe. Fish kills and hydrologic alteration have been occurring in the Des Moines River, which may affect fish condition and truncate size distributions. Therefore, we analyzed stage four--the black egg stage--ovaries from 95 Shovelnose Sturgeon in the Cedar River and 8 Shovelnose Sturgeon from the Des Moines River. We assessed differences in reproductive potential between the populations, by comparing length-based fecundity relationships and length distribution of the adult populations in the two rivers, using regression analyses in program R. Additional sample collection will be completed in the Des Moines and Cedar rivers in the following field season. These results may inform the development of appropriate minimum length limits for recreational or commercial harvest to increase the number of larger females in the population capable of producing more offspring, and to maintain sustainable populations.
