Laboratory studies of potential competition for food and substrate among early juvenile Missouri River sturgeon and sympatric chub species

Abstract

ObjectiveJuvenile Pallid Sturgeon Scaphirhynchus albus predominantly consume midges (family Chironomidae) and other macroinvertebrates, while Shovelnose Sturgeon S. platorynchus, Sicklefin Chub Macrhybopsis meeki, and Shoal Chub M. hyostoma feed on those same macroinvertebrates throughout life. The primary objective of this study was to assess the substrate component of habitat selection, specifically selection between sand and mud substrates, as it relates to food availability and quantity relative to presence or absence of a photoperiod (i.e., lack of light). The study was designed to assess the strength of the innate linkage of substrate and availability of food in foraging by early juvenile Pallid Sturgeon, early juvenile Shovelnose Sturgeon, their juvenile hybrids, and adult Sicklefin Chub and Shoal Chub. The ultimate goal of the study was to develop a better understanding of potential competition for resources among these five fish groups.MethodsTwenty‐four individually isolated aquaria were used to test behavior during a 12 h light : 12 h dark cycle versus continuous darkness. Presence or absence of a photoperiod was combined with feeding levels of maximum ration (Cmax) versus half Cmax ration and the substrate to which food was delivered.ResultFour‐way ANOVA among all five groups and separate ANOVAs for sturgeon and chub groups that included fish group as a factor indicated a selection (i.e., proportion of time over substrate >0.5 given only two substrates equally available) for the substrate to which food was delivered, as expected. However, selection of mud was significantly greater for early juvenile Pallid Sturgeon compared with other fish groups except early juvenile Shovelnose Sturgeon. Neither feeding level nor presence or absence of a photoperiod significantly affected substrate selection. In individual fish group three‐way ANOVAs, Sicklefin Chub did not select a substrate significantly more when food was delivered to the substrate. Shoal Chub selected mud more frequently under continuous darkness. All three sturgeon groups showed a significant increase in weight over time. Only Shovelnose Sturgeon and Sicklefin Chub final weight were significantly greater under Cmax compared to half Cmax. Additionally, early juvenile Pallid Sturgeon, early juvenile Shovelnose Sturgeon, and hybrid sturgeon groups had a greater increase in weight over the study under Cmax than half Cmax.ConclusionWhile caution should always be used when extrapolating results from fine‐scaled, controlled laboratory studies to large, complex river systems, the results from this study support the hypothesis of the potential for competition in the lower Missouri River among the studied fish groups.

Sicklefin Chub (Macrhybopsis meeki) and Sturgeon Chub (M. gelida) Temporal and Spatial Patterns from Extant Population Monitoring and Habitat Data Spanning 23 Years

“…These differences in macrohabitat usage between species suggest that sicklefin chub are more frequently found in main-channel macrohabitats than sturgeon chub. In the laboratory [33], further potential evidence for niche partitioning among our study species comes from the fact that sicklefin chub selection of mud or sand habitat was unaffected by the presence of food, whereas juvenile pallid, shovelnose, and pallid/shovelnose hybrid sturgeon selected habitat with food. The selection for mud over sand was also greater for juvenile pallid sturgeon compared to sicklefin and shoal chub (Macrhybopsis hyostoma) and pallid/shovelnose hybrid sturgeon [33].…”

“…For the three-species models, co-occurrence intercepts for sicklefin chub × sturgeon chub were positive with 95% confidence intervals excluding zero [58]. Predicted marginal occupancy probabilities were significantly higher for sicklefin chub when sturgeon chub were present, and vice versa (Figure 6).…”

“…Shovelnose sturgeon (Scaphirhynchus platorynchus) was included in this study because of its potential for competition for habitat and food resources with sicklefin and sturgeon chub [33] and piscivorous species such as pallid sturgeon, sauger, and walleye. Pallid sturgeon were chosen for their potential roles as competitors to chubs in their juvenile stage and predators of chubs as adults [34,35].…”

“…Walleye and sauger are also important sportfishes [36], whereas pallid sturgeon is a federally listed, endangered species in the United States [35] that preys on focal chub and other small fish to reach adulthood and survive as adults [6,34,35,[52][53][54]. In our comparisons, juvenile pallid sturgeon were considered as a separate USFI from adults because they are less piscivorous and instead as potential competitors for sicklefin and sturgeon chub [33]. The cutoff we used for juvenile pallid sturgeon was total length < 500 mm; pallid sturgeon ≥ 500 mm are almost exclusively piscivorous [6,34,35,[52][53][54].…”

Avoiding a macabre future for Macrhybopsis—A special section on improving management and conservation of chubs

“…Together, these papers will inform Canadian efforts related to the recovery of Silver Chub under the Species at Risk Act. Wildhaber and Alberts (2023, this special section) expand basic ecological knowledge by linking trophic ecology and habitat selection for Sicklefin and Shoal chubs in the Missouri River. Steffensmeier et al (2023, this special section) develop a method for incorporating movement ecology into models describing the distribution of Prairie Chub in the Red River of the South.…”