Diet and Condition of Age‐0 Scaphirhynchus Sturgeon: Implications for Shallow‐Water Habitat Restoration

Abstract

Insufficient food during early life could limit the population growth of endangered Pallid Sturgeon Scaphirhynchus albus in the lower Missouri River. Shallow-water habitat restoration is intended to provide nursery benefits, including food, for young sturgeon, but the effect of shallow-water habitat on their diet is unknown. Age-0 Pallid Sturgeon are rare, providing little opportunity for direct evaluation; however, studying the closely related and abundant Shovelnose Sturgeon S. platorynchus may provide valuable information to guide habitat restoration efforts. We compared diet, body condition (lipid content), and change in body weight (24-h bioenergetics simulation) for postdrift, age-0 sturgeon among five reaches ranging widely in shallow-water habitat availability. Lipid content of satiated and emaciated laboratory-reared individuals were compared with that of wild-caught fish. In general, shallow-water habitat availability appeared to have little effect on the variables examined. Regardless of reach, wild-caught fish primarily consumed chironomids, and empty stomachs were rare. Additionally, differences in prey weight, lipid content, or the modeled change in body weight did not usually correspond to differences in shallow-water habitat availability. Instead, we found annual differences, as prey weight consumed and the percentage of fish with modeled weight gain was often higher in 2015 than 2014, while the opposite was true for the percentage of fish with lipid content values that were comparable with the emaciated laboratory standard. Overall, our findings complement recent suggestions that shallow-water habitat restoration efforts, as previously implemented, may not benefit sturgeon populations. Our results coupled with previous research suggest that the lower Missouri River prey base can support a stable Shovelnose Sturgeon population; however, additional research is needed to determine whether this applies to Pallid Sturgeon.

Differences in macronutrient content of common aquatic macroinvertebrates available as prey for young-of-the-yearScaphirhynchussturgeons in the lower Missouri River

“…Currently, it is not clear if any of the documented foraging locations of shovelnose sturgeon (Scaphirhynchus platorynchus), the pallid sturgeon (Scaphirhynchus albus), and their hybrids produce greater chances of survival compared to others (USACE 2017). Pallid sturgeon are federally listed as endangered and are the main focus of habitat restoration efforts in the LMOR (Civiello et al 2018;USACE 2018;Gemeinhardt et al 2019). Due to similarities in early life history, shovelnose sturgeon are also protected and managed as a surrogate species for pallid sturgeon (Gosch et al 2018).…”

“…Due to similarities in early life history, shovelnose sturgeon are also protected and managed as a surrogate species for pallid sturgeon (Gosch et al 2018). Both species feed primarily on Diptera at the YOY life stage, but will also consume Ephemeroptera and Trichoptera (Civiello et al 2018;. Scaphirhynchus sturgeons have low abundance and poor recruitment (Jacobson et al 2016).…”

“…A major hypothesis for explaining low abundance of Scaphirhynchus sturgeons in the LMOR is that prey quality or availability is limiting juvenile growth and recruitment (Jacobson et al 2016). However, recent studies found the low percentage of empty stomachs and number of food items consumed by Scaphirhynchus sturgeons suggest that food resources are not liming in the LMOR (Gosch et al 2016;Civiello et al 2018). Civiello et al (2018) mentions if food availability during early life history is not a limiting factor, then focusing on other hypothesized factors that influence YOY Scaphirhynchus sturgeons condition (e.g.…”

Dietary assessment of age-0 pallid sturgeon and shovelnose sturgeon: implications for surrogacy

“…Endangered species recovery efforts are often guided by data from surrogates, which are 'species that are used to represent other species or aspects of the environment to attain a conservation objective' (Caro 2010). The surrogate species approach is an attractive option for managers given the limited information available for at-risk species (Murphy et al 2011).…”

“…The surrogate species approach is an attractive option for managers given the limited information available for at-risk species (Murphy et al 2011). However, this approach depends on extrapolation, which involves considerable risk unless the relationship between species has been validated (Caro 2010, Murphy & Weiland 2019. Murphy et al (2011) cautioned that an increasing body of research indicates only marginal success when using a surrogate to guide recovery efforts because a valid surrogate relationship is often assumed.…”