Lake sturgeon (Acipenser fulvescens) sampling techniques on the upper Mississippi River, USA

Lake sturgeon were an important commercial fish in the upper Mississippi River and Great Lakes region during the late 1800's. Because of the high market demand and mismanagement for sturgeon they were soon overexploited. These factors along with deteriorating water quality, habitat destruction, and the building of dams which inhibit upstream movements to spawning areas reduced or extirpated their populations over much of their native range.;In an effort to reestablish populations in the Mississippi and Missouri Rivers and to produce a self sustaining population, the Missouri Department of Conservation began obtaining fertilized eggs and rearing and stocking lake sturgeon in 1984. More than 286,000 lake sturgeon have been stocked since this time. Fish from the first stockings should now be reaching sexual maturity creating a population with varying age classes. Research is now needed to better manage this species for future success. In order to study these animals the first step is to develop the most effective and efficient sampling methods.;In this study I used standard gill nets, hobbled gill nets, trotlines and hoop nets to determine the best gear at catching lake sturgeon during different river conditions. All sampling was conducted from March 2005 to November 2006 in Pool 24 of the Mississippi River.;Over the two years 567 gear sets were deployed capturing 319 lake sturgeon. Sizes ranged from 192 mm/0.1 kg to 1218 mm/14.65 kg. Gill nets had significantly higher catch rates than hoop nets and trotlines. The dam, tailwaters, and wing dike habitats had significantly higher catch rates than the channel border, side channel and main channel habitats, but they were not significantly different from each other.;A General Linear Model (GLM) was preformed (alpha = 0.05) to compare habitat and gear type using temperature, discharge, and depth as covariates. This test resulted in an R-squared value of 0.17. It showed that gear type (p < 0.0001), habitat (p = 0.0017) and temperature (p = 0.0128) all had significant impacts on catch rates, but depth (p = 0.2544) and discharge (p = 0.6848) did not.;Gill nets caught more fish across length classes than any other gear type. Hoop nets caught some of the smallest lake sturgeon but they had relatively low catch rates. The largest lake sturgeon that were captured in gill nets was during the months of March, July, August and September and the smallest were in April. Trotlines captured the largest sturgeon during the month of September and the smallest in the month of April. Trotlines did not catch any lake sturgeon smaller than 300 mm.;A linear regression (p = 0.010) showed mesh size had a positive linear relationship to fork length and resulted in an R-squared value of 0.3889. A t-test showed that the hobbled gill nets had significantly higher catch rates when compared to standard non-hobbled gill nets. There was no significant difference between standard non-hobbled gill nets and trotlines.;Straight 8/0 hooks caught larger fish than circle 11/0 hooks. A t-test found this not to be a significant difference (p = 0.062), but with a difference of 100 mm this could be considered biologically significant. Circle hooks had a higher mean catch per unit of effort than straight hooks, but again a paired t-test found this not to be significant (p = 0.1189).