Spatial Distribution of Drifting Pallid Sturgeon Larvae in the Missouri River Inferred from Two Net Designs and Multiple Sampling Locations

Abstract

Nearly 430,000 larval pallid sturgeon Scaphirhynchus albus (5-13 d posthatch) were released in the Missouri River and allowed to free-drift for 5.7 km and then were sampled at a river bend by boats positioned on the inside-bend, inside-bend channel border, mid-channel, and outside-bend locations of the channel. Boats were rigged with conical nets and rectangle nets designed to sample for drifting pallid sturgeon larvae along the bottom and at the surface of the river to address three objectives: (1) examine the vertical drift behavior of larvae; (2) compare numbers, concentrations, and lengths of larvae between conical and rectangle nets; and (3) examine the lateral distribution of free-drifting larvae. The vertical distribution of larvae was not uniform as nearly all larvae (98%) were sampled in nets fished on the bottom, and larval concentrations (expressed as larvae/m 3 ) were greater in bottom-fished nets. Large-opening rectangle nets (0.375 m 2 ) fished on the bottom sampled greater numbers of larvae than small-opening conical nets (0.196 m 2 ) fished on the bottom; however, larval concentrations were similar between the two net designs. Numbers and concentrations of larvae differed among lateral sampling locations and increased from the inside-bend location to the outside-bend location. Lengths of sampled larvae were similar between net designs and vertical locations in the water column, but larvae sampled at the mid-channel location were slightly smaller than larvae sampled at other lateral locations. These results serve as a guide for sampling larval pallid sturgeon in large rivers. Specifically, sampling adjacent to the bottom in the high-velocity thalweg of the channel maximizes the likelihood of collecting larvae and quantifying numbers of drifting larvae of this federally endangered species.

Age‐0 Sturgeon Accessibility to Constructed and Modified Chutes in the Lower Missouri River

“…Even during high water, these structures may limit age-0 sturgeon access. For example, the majority of free-embryo sturgeon drift is near the bottom (Braaten et al 2008(Braaten et al , 2010, thus, even when these inlet control structures are overtopped during high water, young sturgeon may not be capable of successfully drifting over these structures. Woodward and Rus (2011) found that chute inlet control structures limited the amount of Missouri River course-grained suspended sediment entering Upper Hamburg and Glovers Point chutes, demonstrating the potential barrier that these structures may pose to other objects drifting near the bottom, such as sturgeon larvae.…”

The influence of discharge, current speed, and development on the downstream dispersal of larval nase (Chondrostoma nasus) in the River Danube

“…Stage-specific peculiarities in (active) spatial dispersal cannot be derived from DIFF alone; drift patterns where younger individuals concentrate near the bank and older ones in mid-channel , or vice versa (Braaten et al 2010), could remain concealed. Such characteristics are revealed in the unequal distribution of L2 and L4 nase over the sampling area (i.e., in particular drift nets), potentially originating from differences in behaviour, orientation, and swimming.…”

Patterns and processes in the drift of early developmental stages of fish in rivers: a review

“…groyne fields; Lechner et al 2014a) or be concentrated in dead zones, slackwater habitats (Wolter and Sukhodolov 2008;Kopf et al 2014) and concave riverbanks (Pavlov et al 2008). Depending on discharge levels, hydraulic forces may concentrate young fish in areas with high current speeds, such as the thalweg (Braaten et al 2010;Ellsworth et al 2010a). If larvae are kept in suspension under high discharges, this may considerably increase drift distance and influence longitudinal distribution patterns (Corbett and Powles 1986).…”

“…This information can elucidate patterns and processes associated with spawning and larval production (Zitek et al 2004a;King et al 2005;Braaten et al 2010;Borcherding et al 2014), it may allow forecasting of future year-class-strength (Johnston et al 1995) and provide estimates of stock size of spawning adults (Usvyatsov et al 2013). It also assists in understanding how fishes and their environmentespecially the flow environment-interact.…”