Spatiotemporal variation in density of larval bighead carp in the lower Missouri River

Bighead carp Hypophthalmichthys nobilis, an exotic planktivore, was introduced into Arkansas in 1973 and subsequently dispersed upstream through the Mississippi River and its tributaries. Early life history characteristics of bighead carp in North American rivers have riot been documented. The objectives of this study were to examine the temporal and spatial variation in the density of larvae and to estimate the spawning date of bighead carp in the lower Missouri River. We sampled larval fish once per week at four sites between White Cloud, Kansas, and Lexington, Missouri, from May through July 1997 and 1998. Density of larval bighead carp varied spatially and temporally. Larval bighead carp were collected at all four sites (Lexington, Kansas City, and St. Joseph, Missouri, and White Cloud, Kansas) only on June 25, 1997; on July 2 and 9, 1998, they were collected only at Kansas City and Lexington, Missouri. Density was greatest (24.4 larvae/m(3)) at the most downstream site (Lexington, Missouri) and lowest (0.1 larvae/m(3)) at the most upstream site (White Cloud, Kansas) in 1997. Bighead carp spawning occurred in three distinct periods (June 16-19, 1997; June 23-26, 1998; and July 3, 1998). Spawning in both years occurred in conjunction with an increase in discharge (an increase of 2,764 m(3)/s in 1997 and 3,511 mils in 1998) after water temperatures had stabilized above 22 degreesC. These data suggest a link between water temperature and discharge as spawning cues and successful hatching criteria for bighead carp in the lower Missouri River.