Shovelnose sturgeon Scaphirhynchus platorynchus are commercially important, supporting a viable roe fishery throughout much of the Mississippi River drainage. We examined the reproductive attributes of stage-5 female shovelnose sturgeon captured from the upper Wabash River, Indiana, from March to June 2004. Shovelnose sturgeon were collected using boat electrofishing and experimental gill nets, measured for fork length (FL) and wet weight, and sexed externally if possible. Size-and age-at-maturity, absolute and relative fecundity, relative egg size, and gonadosomatic index (GSI) were determined for 49 female shovelnose sturgeon (range, 601-to 858-mm FL). Female shovelnose sturgeon reached sexual maturity at approximately 600 mm and age-at-maturity ranged from ages 6 to 12 (median age ¼ 9). Relative fecundity ranged from 11 220 to 23 956 eggs kg )1 (mean -18 156 eggs kg )1 ). Absolute fecundity ranged from 14 294 to 65 490 eggs female )1 (mean ¼ 30 397 eggs female )1 ) and was positively related to FL (r 2 ¼ 0.76) and wet weight (r 2 ¼ 0.82). The number of eggs g )1 of ovary weight ranged from 72 to 170 (mean ¼ 98 eggs g )1 ) and was negatively correlated with GSI. GSI values ranged from 9.4 to 27.2 (mean ¼ 19.3) and were positively correlated to FL (r 2 ¼ 0.18). Our results increase our understanding of shovelnose sturgeon reproductive biology and recruitment dynamics and provide input for models to evaluate the effects of harvest on this species.

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 ¼ 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 (<30 years) declines in yield. Further, sensitivity and robustness analyses suggested that the 635-mm minimum length limit would allow population parameters to increase even at the worst-case scenario. As a result, the 635-mm minimum length limit was recommended as the most appropriate regulation to promote conservation and sustainable harvest of shovelnose sturgeon in the upper Wabash River.

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 ¼ 4,849) 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 ¼ 273-858 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.

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