Describing the Diet of Juvenile White Sturgeon in the Upper Columbia River Canada with Lethal and Nonlethal Methods

We describe the overall composition and prey selectivity in the diet of hatchery-reared juvenile White Sturgeon Acipenser transmontanus in the upper Columbia River, Canada. The efficacy of two sampling methods, nonlethal gastric lavage and lethal sampling to remove stomach contents, were evaluated across different ages, size-classes, and river sections. Gastric lavage samples were collected from 108 fish angled in October 2012 and 2013. In 2012 only, a subsample of 48 individuals were euthanized following gastric lavage, and stomach contents were collected. To describe food availability, 45 benthic grabs were collected from areas of juvenile capture. Identifiable prey taxa were recovered from 60.3% of lavage and 98% of lethal stomachs sampled. While the diet of juvenile White Sturgeon was composed of 16 diverse prey taxa, most were selected less than their availability in the river. Prey diversity in lethal samples was influenced by river section, not by fish size or age; fish in deeper, slower water consumed the highest number of prey taxa (mean = 4.6). Further, there was no significant overlap in diets among river sections, the dominant prey taxa selected differing among river sections and years. Prey in the lethal samples included 56% of the 25 total prey taxa identified, lethal included 60%, and the bottom grabs included 76%. Gastric lavage was 69% efficient at describing lethal samples. A minimum of 100 lavage samples were required to describe the diet to a level comparable to lethal sampling. Where lethal sampling is not an option, our results indicate gastric lavage, if conducted on appropriate numbers of fish, is effective at describing sturgeon diets and provides data that can be used to study the feeding ecology of threatened or endangered species.