Habitat Selection and Movement of Naturally Occurring Pallid Sturgeon in the Mississippi River

The pallid sturgeon Scaphirhynchus albus is a U.S. federally endangered species that occurs in the 320-km middle Mississippi River (MMR). Historic in-channel island habitat has vanished, and the extent of the population's range within the MMR is unknown. We surgically implanted ultrasonic transmitters in 88 adult pallid sturgeon (>600 mm fork length; mean = 791 mm) during 2002-2005 and used boat-mounted hydrophones to quantify their seasonal use of major MMR habitat features (wing dikes, side channels, island side channel tips, tributaries, and main channel; total of 8,629 river kilometers monitored). Distance from habitat features (gravel bars, wing dikes, and island side channels) was quantified during spring, a period considered to be critical for many fish species. We quantified maximum seasonal movement of each fish in the entire MMR with stationary data-logging hydrophones during 2004-2006. Combining data across years and seasons, we found that pallid sturgeon selected the tips of wing dikes over other habitat features. However, during spring pallid sturgeon moved from the tips of wing dikes to within about 100 m of known gravel bars. Maximum distance moved by pallid sturgeon varied the most in spring relative to other seasons. One pallid sturgeon moved through the entire study reach, and a few individuals left the MMR for the Missouri River or the lower Mississippi River. Unique flow and substrate characteristics of wing dikes probably emulated missing habitat complexity (i.e., in-channel islands, deep scour holes, and sand bars). Other habitats such as gravel bars may be important during spring, although their contributions to reproduction, foraging, and survival of pallid sturgeon are unknown. The range of this pallid sturgeon population extends beyond the entire stretch of the MMR into other river basins; thus, the population requires rangewide management.