Potential Minimum Threshold for Pallid Sturgeon Relative Condition in the Lower Missouri River

Abstract

Pallid Sturgeon (Scaphirhynchus albus) condition has declined in the lower Missouri River but the cause and the effects of this decline remain uncertain. Adult Pallid Sturgeon are becoming reproductively ready less frequently and sub-adult Pallid Sturgeon are likely delaying sexual maturation. Even more concerning, Pallid Sturgeon capture rates have declined the past two years (i.e., 2016 and 2017), despite the ongoing Pallid Sturgeon stocking program. Several Pallid Sturgeon that have been captured are visually emaciated but a minimum condition threshold has not been described. Therefore, the aim of this study is to present a potential lethal condition level for adult Pallid Sturgeon in the lower Missouri River then determine the capture frequency of Pallid Sturgeon below this assumed minimum condition threshold to test the validity of this hypothesis. Based on the mortality of an individual female adult Pallid Sturgeon held in captivity, mortality occurred when condition was 0.71. This potential minimum threshold is further supported with very few adult Pallid Sturgeon captured below this predicted minimum threshold. Using the minimum condition threshold established here to continue monitoring the Pallid Sturgeon population and the occurrence of individuals below this condition level could help managers better address factors hindering Pallid Sturgeon recovery.

Mismatch between temperature and discharge disrupts spawning cues in a fluvial specialist, blue sucker Cycleptus elongatus

“…However, since the early 1900s, a dramatic decrease in blue sucker populations has been observed (Coker, 1930; Pflieger, 1997; Vokoun et al, 2003), and this decline has continued even after the cessation of commercial fishing in most systems (Pflieger, 1997; USFWS, 1993). Today, the blue sucker is listed as a species of greatest conservation need, threatened, presumed extirpated or endangered in 19 of the 23 states where they are known to occur (Steffensen et al, 2015). Limited research has been focused on the spawning cues of the species, but it is assumed that the species' diminished range and population sizes are a result of habitat fragmentation, reduced spawning habitat, discharge regime and temperature alterations (Acre et al, 2021; Pflieger, 1997; Warren & Burr, 2014).…”

Validation of a microwave energy meter to non-lethally estimate energetic reserves in adult sturgeon

“…Whole-body (WB) energetic reserves have important influences on physiological processes governing survival, growth, and reproduction ( Kooijman, 2009 ; Deslauriers et al, 2016 ). Shortages of energetic reserves can constrain survival ( Randall et al, 2017 ; Steffensen, 2018 ), metabolism ( Daigle et al, 2021 ), and reproduction ( Barneche et al, 2018 ) across a large array of fish taxa. WB energetic reserves are typically determined through lethal methods ( i.e.…”

“…In addition, the mechanisms underlying the variation in size- and age-at-first-maturity among pallid sturgeon populations inhabiting the Missouri and Yellowstone Rivers above Fort Peck Reservoir, the Missouri River below Fort Peck, and captive pallid sturgeon are not fully understood ( Hamel et al, 2014 ; Jordan et al, 2016 ; Holmquist et al, 2019 ; Hamel et al, 2020 ; Cox et al, 2022 ) and is likely related to the maintenance and accumulation of WB energetic reserves. Furthermore, pallid sturgeon relative condition (Kn; the ratio of the observed body mass [BM] to the length-based predicted BM for a fish) has been declining since 2004, and from 2012 to 2015, a small number of extremely emaciated pallid sturgeon were observed in the lower Missouri River ( Steffensen and Mestl, 2016 ; Steffensen, 2018 ).…”

Demographics, Reproductive Characteristics, and Genetic Connectivity of Blue Suckers (Cycleptus elongatus) in a Large Tributary

“…Largely restricted to the highly altered Mississippi River basin and several Gulf Coast drainages, Blue Suckers have declined in abundance due to habitat degradation, loss of habitat connectivity, and anthropogenic flow modifications (Smith, 1979; Cooke et al, 2005; Acre et al, 2021). Blue Suckers are known to make annual migrations of up to 545 km for spring spawning events (Bednarski and Scarnecchia, 2006); however, many extant populations are restricted in impounded segments of river with limited access to diverse habitats (Rupprecht and Jahn, 1980; BIO-WEST, 2006; Steffensen et al, 2015; Acre et al, 2021). When connectivity is lost, isolated populations can lose genetic diversity at an accelerated rate through random sampling via genetic drift, leading to genetic impoverishment, inbreeding, and decreased fitness at both the individual and population level (Steffensen et al, 2015; McIntyre et al, 2016; Zarri et al, 2022).…”

“…Blue Suckers are known to make annual migrations of up to 545 km for spring spawning events (Bednarski and Scarnecchia, 2006); however, many extant populations are restricted in impounded segments of river with limited access to diverse habitats (Rupprecht and Jahn, 1980; BIO-WEST, 2006; Steffensen et al, 2015; Acre et al, 2021). When connectivity is lost, isolated populations can lose genetic diversity at an accelerated rate through random sampling via genetic drift, leading to genetic impoverishment, inbreeding, and decreased fitness at both the individual and population level (Steffensen et al, 2015; McIntyre et al, 2016; Zarri et al, 2022). The Mississippi River basin may support a continuous metapopulation of Blue Suckers (Buth and Mayden, 2001; Bessert, 2006), but river fragmentation has led to genetic isolation-by-distance in individuals occupying impounded tributaries (Bessert and Ortí, 2008).…”