Population characteristics of shovelnose sturgeon in the upper Wabash River, Indiana

Shovelnose sturgeon Scaphirhynchus platorynchus support a commercial fishery throughout much of the Mississippi and Missouri River drainages. There is concern that harvest closures for Eurasian sturgeons (Acipenseridae) may result in increased exploitation of shovelnose sturgeon to meet global demands for caviar. Population attributes of shovelnose sturgeon were examined in the upper Wabash River, Indiana, from April 2003 through November 2004 between Wabash and Terre Haute. Fish (N = 4,949) were captured by direct current electrofishing, experimental gill nets, and benthic trawls. Electrofishing catch per unit effort varied on a temporal basis, being highest for both reaches from March through May. The fork length of captured fish ranged from 273 to 858 mm, but few fish less than 550 mm were captured. Median fork length and wet weight were 683 mm and 1,208 g, respectively (ranges = 273-958 mm and 52-3,381 g). Shovelnose sturgeon ranged from ages 2 to 30, with 95% of the fish between ages 9 and 20. Total annual mortality for fish between ages 13 and 18 was 20%. Empirical growth rates derived from recaptured fish were slow; 74% of the fish exhibited negative or no growth. The population characteristics of shovelnose sturgeon in the upper Wabash River were within the ranges reported for other river systems, but fish attained a larger body size, reached older age-classes, and experienced lower mortality rates than did some other populations. The results from this study will allow for the detection of shifts in abundance, size and age structure, and gender ratio in response to harvest or natural perturbations and promote the development of appropriate management actions to ensure the sustainability of this species and its fishery.