Seasonal Diet Composition of Adult Shovelnose Sturgeon in the Middle Mississippi River
Seibert, Justin R., Phelps, Quinton E., Tripp, Sara J., Garvey, James E., The American Midland Naturalist
Because the shovelnose sturgeon (Scaphirhynchus platorynchus) population in the Middle Mississippi River (MMR) between Cairo, IL and St. Louis, MO (RKM 0-320) appears to be declining, we must understand dietary needs to help assess its conservation status. Diet is linked to growth, condition and reproduction and reflects population state. Thus, we quantified diets of adult shovelnose sturgeon monthly using gill nets (5.08-cm bar mesh) during Jan. 2005 through Nov. 2005 at three sites on the MMR (RKM: 201-198; 191188, and RKM 127-124). Stomachs were removed from adult shovelnose sturgeon (winter n = 71; spring n = 163; summer n = 149; fall n = 179; fork length mean = 617 mm; standard deviation = 64.57). Overall, prey items occurred in less than 30% (n = 170) of shovelnose sturgeon stomachs. Dominant prey items throughout all seasons (winter, spring, summer and fall) were Chironomidae, Hydropsychidae, Ephemeridae and Corophiidae respectively. Corophiidae is an exotic amphipod that has not previously been documented in the MMR. The total abundance of diet items was high during winter through spring and low during summer through fall. Ephemeridae dominated in winter. Hydropsychidae was the most important prey item during spring through summer. Corophiidae dominated diets in the fall. Temperature and perhaps low river discharge appeared to affect prey consumed, with high temperatures and low discharge during summer through fall causing low energy intake, lowered condition and likely poor growth. Conservation efforts that provide flow refugia may improve energy intake and likely enhance shovelnose sturgeon populations in the MMR.
Due to commercial harvest and habitat degradation worldwide, sturgeon numbers have been declining for nearly 100 y (Keenlyne, 1997; Shuman, 2003). Mature female sturgeon are selectively harvested for caviar, rendering populations especially vulnerable. Because sturgeon delay sexual maturity, reproductive potential is further reduced by selective harvest (Colombo et al, 2007; Tripp et al, 2009a). This reproductive loss coupled with habitat degradation has led to the collapse of multiple sturgeon populations and may be threatening one of the last commercially viable populations in the world (Billard and Lecointre, 2001; Ludwig et al, 2002; Secor et al, 2002; Tripp el al, 2009a, b). Shovelnose sturgeon Scaphirhynchus platorynchus are the most abundant member of the family Acipenseridae within the Mississippi River and support commercial fisheries in portions of the Mississippi and Missouri rivers (Kline and Golden, 1979; Carlson et al, 1985; Hurley et al, 1987). In the free-flowing Middle Mississippi River extending from Cairo, Illinois to St. Louis, Missouri (MMR; RKM 0-200) shovelnose sturgeon populations have declined perhaps due to habitat degradation and commercial harvest (Keenlyne, 1997; Morrow et al, 1998; Jackson, 2004; Colombo et al, 2007; Tripp el al, 2009a, b) . Market price for shovelnose sturgeon eggs is high compared with other commercial fish species in the Mississippi River basin (Becker, 1983). In order to maintain a harvestable shovelnose sturgeon population, we need to eventually understand their life historv, which guides management and ultimately drives regulations.
As with all organisms, energy intake affects shovelnose sturgeon growth and survival. Diet composition and quantity can dramatically influence condition and thus influence reproduction. Shovelnose sturgeon diets have been quantified in several large rivers: Platte River (Shuman, 2003), upper Mississippi River (Hoopes, 1960; Helms, 1974; Carlson et al, 1985), and Missouri River (Held, 1969; Modde and Schmulbach, 1977; Carlson et al, 1985; Megargle, 1997; Berry, 2002; Braaten et al, 2006; Wanner et al, 2007). Although many shovelnose sturgeon diet studies have been completed, we are unaware of any studies that have been conducted in the MMR, which is free-flowing and geologically unique to the remainder of the Mississippi River drainage. …