Effects of harvest and length limits on shovelnose sturgeon in the upper Wabash River, Indiana

Shovelnose sturgeon Scaphirhynchus platorynchus are one of the few sturgeon species that currently support sustainable commercial harvest. However, harvest closures for many Eurasian sturgeons have resulted in increased exploitation of this fishery, thereby raising concerns about the sustainability of shovelnose sturgeon resources. As a result, the maintenance of self-sustaining shovelnose sturgeon populations will require the estimation of appropriate harvest levels. This study used an age-structured population model to examine the effects of harvest (u = 0.15-0.75) and length restrictions on population abundance, mean length-at-harvest, biomass, yield, and reproductive potential of female shovelnose sturgeon in the upper Wabash River, Indiana. Model simulations for four hypothetical length-restriction scenarios (610- to 813-mm reverse slot limit, and a 610-, 635-, and 660-mm minimum length limit) were compared to outputs with no restriction. All population parameters within each length-restriction scenario declined with increases in harvest level. For each harvest level, all population parameters increased as length limits became more restrictive. The reverse slot limit and 610-mm minimum length limit provided adequate protection to allow population parameters to increase through an annual harvest level of 0.55. However, these length restrictions were not sufficiently conservative to warrant implementation due to their similarity to length-at-maturity of female shovelnose sturgeon. The implementation of a 635-mm minimum length limit would protect female shovelnose sturgeon from harvest rates >0.75, allow 92% of the females to remain available for harvest, and minimize short-term (