Cooperative Fish and Wildlife Research Units Program: Montana Fishery
Education, Research and Technical Assistance for Managing Our Natural Resources

Project Summary: This project will evaluate the diets of pallid sturgeon (Scaphirhynchus albus) in the Missouri River above Fort Peck Reservoir using stable isotopes (i.e., longer-term integration of food habits) and real-time gut contents (i.e., short-term integration of food habits). Diet data will be evaluated by year-class (age), size (length, weight), river location (longitudinally), seasons, and with historical data from Gerrity et al. (2006). These data will be paired with contemporary and historical (Grisak 1996) catch-per-unit effort data for sicklefin chub (Macrhybopsis meeki) and sturgeon chub (Macrhybopsis gelida). The information from this study will provide insight into the contemporary importance of sicklefin chub and sturgeon chub in the diets of pallid sturgeon and whether the conclusions determined by Gerrity (2006) are still relevant for this reach of the Missouri River. These results will also be compared to diet data for pallid sturgeon sampled below Fort Peck Reservoir (see Dutton 2018) to make larger inferences about pallid sturgeon feeding ecology. Furthermore, these data will provide information on the relationship between diet and variability in growth. That is, are slow growing pallid sturgeon within a year-class primarily feeding on macroinvertebrates? Conversely, are fast growing pallid sturgeon within a year-class primarily feeding on fish? The need for this information is timely given the proposed listing of sicklefin chub and sturgeon chub and the continued questions surrounding variation in growth and carrying capacity of hatchery-reared pallid sturgeon.

Objectives: The objective of this project is to describe the diets of pallid sturgeon using stable isotopes and gut-content analysis and relate those data to year-class, size, river location, season, contemporary and historical catch-per-unit effort data for sicklefin and sturgeon chub, and with historical data from Gerrity et al. (2006).

Reference to 10-year Strategy and Recovery Plan:By understanding the diets of pallid sturgeon and the contemporary importance of sicklefin chub and sturgeon chub for the species, we will address three of the five primary strategies for recovery of pallid sturgeon listed in the Revised Recovery Plan (USFWS, 2014), specifically 2) fully quantify population demographics and status within each management unit; 3) improve population size and viability within each management unit; and 4) reduce threats having the greatest impact on the species within each management unit. The results will also address all three of the main goals of the Upper Basin Pallid Sturgeon Workgroup 10-year Strategy, specifically 1) documentation of natural reproduction and survival of wild produced pallid sturgeon in each RPMA at sufficient levels to sustain the population, 2) promote and initiate conservation, restoration, or management actions that improve habitat conditions for pallid sturgeon to complete their entire life cycle as well as targeted research to address impediments and knowledge gaps to the ultimate recovery of the species, and 3) promote collaboration, cooperation, and communication of pallid sturgeon recovery needs and proposed actions amongst resource agencies, universities, and affected stakeholders.

Approach: Pallid sturgeon will be sampled throughout the Missouri River from the confluence of the Marias River to the transition zone with Fort Peck Reservoir using a systematic sampling design. Pallid Sturgeon will be sampled with drifted trammel nets (45.72-m long, 1.8-m high, and 25.4-mm or 50.8-mm inner mesh) or benthic beam trawls (1.8-m x 0.46-m frame with 3.2- mm inner mesh cod end). A systematic sampling design will be implemented that focuses effort
in reaches where pallid sturgeon catch rates have been high in previous years and benthic trawling can be used (i.e., lack of boulders and large cobble). Sampling reaches of interest include the 97-km reach immediately upstream of Fort Peck Reservoir, the Missouri River near Judith Landing, and the Missouri River and lower Marias River near Loma, Montana. In addition, sampling locations will be paired with contemporary and historical sampling locations for sicklefin chub and sturgeon chub. All sampled pallid sturgeon will be handled in accordance with the current handling protocols for pallid sturgeon (USFWS 2014). Pallid sturgeon will be removed from the sampling gear immediately and placed in a tank filled with river water. Fish will be measured, weighed, checked for marks (elastomer or missing scutes), and scanned for an existing PIT tag. If no PIT tag is found, a new tag will be installed and a genetics sample will be collected in accordance with the handling protocols. Pallid sturgeon will be sampled for stable isotopes with either an epidermal mucous sample, muscle plug (~ 10 g), or fin clip (Andvik et al. 2010) and gut contents (identified to lowest taxon) will be removed using a gastric lavage (see Dutton 2018). Stable isotopes will be analyzed at the University of Wyoming Isotope Facility.
Nitrogen isotope ratios accumulate about 3.4% per trophic level and carbon isotope ratios indicate the location from which consumers obtain energy. We will use stable isotope analyses (i.e., δ¹³C and δ¹⁵N) and gut-content analyses to describe trophic position and diet data (long term and short term). These data will be analyzed by year-class, size, and river location to build an ontogenetic-spatiotemporal model of how pallid sturgeon use food resources throughout the upper Missouri River. Furthermore, we will use gut-content analysis to estimate the importance (e.g., percent composition) of sicklefin chub and sturgeon chub in the diet of pallid sturgeon and relate those results to historical diet data and samples of sicklefin chub and sturgeon chub.