Population characteristics of exploited shovelnose sturgeon and assessment of a bridge-mounted hydroacoustic telemetry array on the lower Mississippi River, Tennessee

Populations of sturgeons are being overfished as worldwide demand for caviar, a product of sturgeon roe, continues to increase. The commercial shovelnose sturgeon Scaphirhynchus platorynchus fishery in Tennessee is driven by caviar production; however, growth, mortality, and the effectiveness of current harvest regulations have not been studied. Data from shovelnose sturgeon (n = 486) collected from Tennessee Wildlife Resource Agency biologists and commercial fishers using trot lines and gillnets were used to estimate the growth and mortality of shovelnose sturgeons in the Tennessee waters of the Mississippi River. Ages of shovelnose sturgeons ranged from 3 to 16 years. Shovelnose sturgeon were fully recruited to the gear at age 10 and the interval mortality rate between ages 10 and 16 was 57%. The yield and spawning potential ratios for the population were simulated with a minimum length limit of 610 mm fork length (the lower limit of the current harvest slot limit) and at higher and lower minimum length limits. Simulated yields and spawning potential ratios did not indicate growth or recruitment overfishing at levels of exploitation less than 60%.;Movements of the federally endangered pallid sturgeon S. albus in the Mississippi River are poorly understood. Efforts to track sonic tagged pallid sturgeon using submersible acoustic receivers attached beneath buoys have yielded poor receiver retrieval rates. To prevent the loss of receivers, a mounting system consisting of lengths of conduit with the receiver placed inside has been used to attach arrays of receivers to the downriver side of bridge piers throughout the Mississippi River. From August 2007 to August 2008, tests were conducted by moving a submersed pinger tag downriver past receiver arrays on three bridges over the Mississippi River at high and low river stages. Maximum tag detection distance ranged from 51 m to 335 m, with a maximum detection area of less than 0.01 ha to 2.86 ha. Observed receiver detection areas did not extend to the nearest bank at any of the bridges tested in Tennessee; therefore, total channel coverage by receiver arrays is not possible. Detection by bridge mounted receivers was negatively affected by the receiver's proximity to the main channel and by higher water stages, likely due to the high ambient acoustic background present near the main channel, an effect that is amplified by high river stages. Current technologies and receiver-attachment schemes cannot guarantee the detection of acoustically-tagged pallid sturgeons moving up or down the Mississippi River.