Scaphirhynchus Conference: Alabama, Pallid, and Shovelnose Sturgeon

St. Louis, Missouri, 11-13 January 2005

6. MORPHOMETRIC VARIATION AMONG SCAPHIRHYNCHUS SPECIMENS IN THE LOWER AND MIDDLE MISSISSIPPI RIVER

Catherine E. Murphy*, U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Road, EE-A, Vicksburg, MS 39180-6199; Phone 601-634-4233; Fax 601-634-3560; Catherine.E.Murphy@erdc.usace.army.mil

Jan Jeffrey Hoover, U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Road, EE-A, Vicksburg, MS 39180-6199; Phone 601-634-3996; Fax 601-634-3560; Jan.J.Hoover@erdc.usace.army.mil

Steven G. George, U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Road, EE-A, Vicksburg, MS 39180-6199; Phone 601-634-2897; Fax 601-634-3560; Steven.G.George@erdc.usace.army.mil

K. Jack Killgore, U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Road, EE-A, Vicksburg, MS 39180-6199; Phone 601-634-3397; Fax 601-634-2398; Jack.Killgore@erdc.usace.army.mil

Pallid sturgeon (Scaphirhynchus albus) captured in the middle and lower Mississippi River (below St. Louis, MO) often appear morphologically indistinguishable from shovelnose sturgeon (S. platorynchus).  Available empirical data from a handful of studies on pallid sturgeon are based on a few specimens from disjunct populations and geneticists are currently searching for markers that will differentiate the two species, but the need for unequivocal species-specific field characters remains.  Continuation of commercial fishing for shovelnose sturgeon in some states necessitates an immediate means for accurate field identifications.  Character indices that employ a selection of simple morphological measurements work well to classify individuals, but advocate the concept of inter-specific hybridization between pallid and shovelnose sturgeon.  Morphometric variation among Scaphirhynchus specimens from the middle and lower Mississippi River is examined for evidence of inter-specific hybridization.  Data are compared from four different groups of specimens: mature sturgeon collected during preliminary studies in the lower river, juvenile shovelnose collected in the lower river, juvenile pallids collected from various hatcheries throughout the range, and sturgeon tagged and released throughout the lower and middle Mississippi River during 2000-2004.  Measurements are presented as a proportion of head or standard length and compared for each group of specimens.  Results indicate that use of certain morphometric ratios may reduce bias from allometric growth and that inter-specific hybridization is less probable in the unimpounded populations of the middle and lower Mississippi River.