Abstract
Acipenseriformes (sturgeons and paddlefish) globally have declined throughout their range due to river fragmentation, habitat loss, overfishing, and degradation of water quality. In North America, pallid sturgeon (Scaphirhynchus albus) populations have experienced poor to no recruitment, or substantial levels of hybridization with the closely related shovelnose sturgeon (S. platorynchus). The Lower Missouri River is the only portion of the species’ range where successful reproduction and recruitment of genetically pure pallid sturgeon have been documented. This paper documents spawning habitat and behavior on the Lower Missouri River, which comprises over 1,300 km of unfragmented river habitat. The objective of this study was to determine spawning locations and describe habitat characteristics and environmental conditions (depth, water velocity, substrate, discharge, temperature, and turbidity) on the Lower Missouri River. We measured habitat characteristics for spawning events of ten telemetry-tagged female pallid sturgeon from 2008–2013 that occurred in discrete reaches distributed over hundreds of kilometers. These results show pallid sturgeon select deep and fast areas in or near the navigation channel along outside revetted banks for spawning. These habitats are deeper and faster than nearby river habitats within the surrounding river reach. Spawning patches have a mean depth of 6.6 m and a mean depth-averaged water-column velocity of 1.4 m per second. Substrates in spawning patches consist of coarse bank revetment, gravel, sand, and bedrock. Results indicate habitat used by pallid sturgeon for spawning is more common and widespread in the present-day channelized Lower Missouri River relative to the sparse and disperse coarse substrates available prior to channelization. Understanding the spawning habitats currently utilized on the Lower Missouri River and if they are functioning properly is important for improving habitat remediation measures aimed at increasing reproductive success. Recovery efforts for pallid sturgeon on the Missouri River, if successful, can provide guidance to sturgeon recovery on other river systems; particularly large, regulated, and channelized rivers.
Highlights
Most species of Acipenseriformes are considered highly threatened globally; 24 of the 27 species are listed by the International Union for the Conservation of Nature (Cooke, Paukert, & Hogan, 2012)
Spawning patches are highly modified habitats at the base of, or adjacent to, coarse bank revetment installed during 20th century channelization
The deep, high-velocity habitats near coarse substrates that comprise present-day, pallid sturgeon spawning habitat are common on the Lower Missouri River (LMOR) (Bulliner, Elliott, & Jacobson, 2017; Reuter et al, 2008)
Summary
Most species of Acipenseriformes (sturgeons and paddlefish) are considered highly threatened globally; 24 of the 27 species are listed by the International Union for the Conservation of Nature (Cooke, Paukert, & Hogan, 2012) (https://www.iucnredlist.org/). The pallid sturgeon (Scaphirhynchus albus) is a long-lived, largeriver obligate species, native to the swift, turbid waters of the Missouri River, the Middle to Lower Mississippi River and some large tributaries from Montana to the Gulf of Mexico (Jordan et al, 2016; Kallemeyn, 1983). Pallid sturgeon populations declined through the 1900s and the species was listed as endangered under the U.S Endangered Species Act in 1990 (USFWS, 1990). Given small population sizes with few reproductive adults, the apparent paucity of natural reproduction and recruitment in the Lower Missouri River (LMOR) nearly 30 years after listing is concerning from a species conservation perspective (Steffensen et al, 2019), (Figure 1)
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