Seasonal diet composition of juvenile and adult pallid sturgeon,Scaphirhynchus albus(Forbes & Richardson, 1905), in the channelized lower Missouri River

Abstract

Summary Although habitat alterations and reproductive success are the main contributors to declines of the pallid sturgeon, Scaphirhynchus albus (Forbes & Richardson, 1905) listed in 1990 as federally endangered, disrupted trophic links within diets of pallid sturgeon populations have been hypothesized as partial contributors. The objective of this study was to evaluate pallid sturgeon food habits within a 500 km reach of the lower channelized Missouri River using non-lethal pulsed gastric lavage. Trotlines, gill nets, trammel nets, and benthic otter trawls were used to collect 284 pallid sturgeon, which ranged in fork length from 265 to 1047 mm. Stomach contents of pallid sturgeon included fish (Cyprinidae and Ictaluridae), aquatic insects, copepods, leeches, and mussels. Cyprinids were the most abundant prey item; ictalurids were also of high abundance. Otter trawl catch rates of ictalurids and cyprinids were not spatially correlated to the respective abundances in pallid sturgeon diets; however, the ratio of the average catch rate to the average number of fish per pallid sturgeon indicated preference for cyprinids (1.5 : 1), particularly Macrhybopsis species, relative to ictalurids (7 : 1). Our results support the need for management of native cyprinids, especially Macrhybopsis species, which have been in decline within the entire range of the pallid sturgeon. However, pallid sturgeon are also able to consume ictalurids, a species which has remained in high abundance in the lower Missouri River.