Catch Rates for Sturgeon Chubs and Sicklefin Chubs in the Upper Missouri River 2004–2016 and Correlations With Biotic and Abiotic Variables

Abstract

A multiweek standardized sampling regime during 2004–2016 in a 60-km reach of the Upper Missouri River assessed reproduction and catch rates for Sturgeon Chub Macrhybopsis gelida and Sicklefin Chub Macrhybopsis meeki. We sampled age-0 Macrhybopsis (primarily Sturgeon Chubs, but potentially including Sicklefin Chubs) all years to indicate successful reproduction, but noted an inverse correlation of catch per unit area (CPUA) with year. There was an inverse correlation for CPUA of age-1+ Sturgeon Chubs with year. There was no correlation for CPUA of age-1+ Sicklefin Chubs with year, but we noted a depression in CPUA during 2010 and 2012. The study reach includes restoration directives for federally endangered Pallid Sturgeon Scaphirhynchus albus, with 245,000 hatchery-origin Pallid Sturgeon (HOPS) stocked since 1998 to supplement the declining wild stock. Pallid Sturgeon longer than 350 mm transition to piscivory and are known to prey on Sturgeon Chubs and Sicklefin Chubs. We examined the hypothesis that mass additions of HOPS to the existing predator community could have population-level effects on the two chub species. Population modeling for the stocked HOPS through time yielded estimates of nearly 1,300 piscivore-sized HOPS in 2004, an increase to 26,000 HOPS in 2012, and decreasing numbers through 2016 (14,500). Candidate variables that also included discharge and water temperature best supported a negative correlation between HOPS abundance and age-0 Macrhybopsis CPUA. We found an inverse correlation for CPUA of age-1+ Sturgeon Chubs and estimated HOPS abundance, and there was also evidence of an inverse association between age-1+ Sicklefin Chub CPUA and HOPS in the study area. Results for a 60-km reach of the Upper Missouri River suggest declining CPUA for age-0 Macrhybopsis and Sturgeon Chubs during 2004–2016 and modest recovery of Sicklefin Chubs after 2012. Although causative factors driving CPUA changes through time are not known, correlative analyses suggest that large numbers of HOPS added to the Missouri River predator community potentially influence CPUA of Sturgeon Chubs and Sicklefin Chubs in the study area. Testing this hypothesis will require expanded quantification of chub populations and HOPS numbers through time.

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

“…We found sicklefin chub annual occupancy coefficients were more variable and showed a pattern of higher occupancy rates around 2003-2005 and 2014-2016 for sicklefin chub, compared to other years. This result is also supported by [15], which found no significant correlation between catch rate and year for sicklefin chub in the UMR but noted lower catch rates in 2010 and 2012. Data from a longer time period, as well as information on potential population drivers such as food availability and patterns from other small fish species, would increase temporal predictive ability for the species.…”

“…Due to the sampling design of the PSPAP, where the same sites were not sampled every year, these changes in occupancy coefficients represent changes in the overall proportion of occupied sites per year rather than the extirpation or colonization of specific sites and, potentially, changes in population size [25]. This potential decline in occupancy matches with results reported by [15], based on sampling 60 km of the MR just above the confluence with the Yellowstone River (YR) downstream toward Lake Sakakawea, which found the catch rate of sturgeon chub in the UMR both from age 0 to 1 and over 1 year old was negatively correlated with passing years from 2004 to 2016. We found sicklefin chub annual occupancy coefficients were more variable and showed a pattern of higher occupancy rates around 2003-2005 and 2014-2016 for sicklefin chub, compared to other years.…”

“…Previous research based on PSPAP data [3] documented a pattern of decline in UMR sicklefin chub relative abundance starting in 2003 through 2010, which coincided with increased pallid sturgeon stocking in the UMR [7]. This pattern of decreased sicklefin chub relative abundance with increased stocking of pallid sturgeon, along with one for sturgeon chub, in the UMR was also demonstrated by [15]. In our analysis, this pattern is seen in our annual occupancy coefficients for sicklefin chub, with lower occupancy in the late 2000s into the early 2010s followed by what appears to be a partial recovery in the mid-to-late 2010s despite continued stocking of pallid sturgeon.…”

“…Since the MR represents a major portion of the historical range of both species [14], these data can provide valuable insight into their management. Previous studies using these data have documented declines in sicklefin and sturgeon chub populations [3,15], along with other anecdotal observations from practitioners.…”

“…These variables were the only site-level environmental variables consistently collected by the PSPAP [3]; they were also among the environmental variables collected by the MRBFS [13]. Depth, velocity, turbidity, and temperature have all been shown to affect the presence or spawning of sicklefin chub, sturgeon chub, and similar species [13,15,44]. As temperature and depth are related to the co-occurrence patterns of other fish species [45]; we hypothesized that these factors-along with velocity and turbidity-could also affect the co-occurrence of focal chub species.…”