Habitat Use during Early Life History Infers Recovery Needs for Shovelnose Sturgeon and Pallid Sturgeon in the Middle Mississippi River

Habitat use by wild age-0 shovelnose sturgeon Scaphirhynchus platorynchus and pallid sturgeon S. albus was quantified by trawling macrohabitats (i.e., main channel, main-channel border, island, and artificial structures [e. g., wing dams]) in the middle Mississippi River during 1998-2007 (1,702 trawls; n = 1,507 age-0 sturgeon captured). Age-0 sturgeon catch rates were highest around artificial structures and island areas, while main-channel habitat provided the lowest catch rates. Moreover, size-selective macrohabitat analyses indicated that small age-0 sturgeon (i.e., majority < 50 mm total length) were located in channel-border dike and island side-channel macrohabitats, while all other macrohabitats were occupied by small and large age-0 sturgeon. Furthermore, our analyses indicated that age-0 sturgeon mesohabitat use within macrohabitats was influenced by depth, substrate, and bottom velocity. Low velocity (i.e., similar to 0.1 m/s), moderate depths (i.e., 2-5 m), and sand substrate were positively related to age-0 sturgeon relative abundance. As such, instream habitat modifications that provide the correct combination of macrohabitats with suitable mesohabitats may hold high densities of age-0 shovelnose sturgeon and pallid sturgeon and may improve recruitment success.