Stocking of age-0 pallid sturgeon has been proposed as a way to alleviate high fish densities at hatcheries and potentially enhance stocking success in the wild. However, vulnerability of age-0 pallid sturgeon to fish predation is not known, thus hindering management decisions about when, where, and at what size age-0 pallid sturgeon should be stocked. Determining the relative vulnerability of different sized age-0 pallids to fish predation would help restoration efforts tailor stocking strategies that maximize survival. The external morphology of sturgeons (i.e., bony scutes) likely plays a defensive role against predation that increases in effectiveness with body size. Turbidity can also influence fish predation and varies considerably across the upper Missouri River.
Ontogenetic diet shifts are important events in the early life history of many fishes that can subsequently determine recruitment success. Adult pallid sturgeon are known to be piscivorous, but the size and age at which juveniles switch from feeding on macroinvertebrates to fishes is unknown. Currently, pallid sturgeon biologists hypothesize that this diet shift occurs at age three to five with an associated increase in mortality of 25% and this mortality rate is used to set minimum stocking levels (Kapuscinski 2002; UBPSWG-Stocking Committee 2004). No data currently exists to support this hypothesis. Shovelnose sturgeon feed primarily on macro-invertebrates, but fish are also occasionally found in their diet, making this species a potential competitor with juvenile pallid sturgeons.
The objectives of this study are to: 1) quantify predation vulnerability of age-0 pallid sturgeon as influenced by body size, water turbidity and predator composition and 2) estimate and compare trophic position of pallid sturgeon and shovelnose sturgeon using stable isotope analysis.