If you build it, will they come? Spawning habitat remediation for sturgeon

Abstract

Summary Habitat loss is a widely recognized contributor to global declines in sturgeon populations yet habitat remediation has been limited for this highly endangered group of fish. In support of future sturgeon restoration efforts, this review examines habitat remediation needs and uncertainties. Consideration of the bio‐spatial scale of remediation identified needs ranging from local to the whole river scale. Additionally, the context of remediation ranges from reintroducing sturgeon to habitats where they have been extirpated to conservation of currently functional habitat. While multiple remediation scales and contexts are discussed, the focus on spawning and early rearing habitat and associated biological and physical monitoring reflects the range of current projects and the importance of early rearing habitats. Four case studies are presented that examine four distinct remediation contexts (mitigation, rejuvenation, re‐creation, repatriation) and three bio‐spatial scales (whole river, spawning reach, spawning location) under which remediation has been attempted. Evaluation of existing remediation works indicates that many show limited long‐term success, which is most often a response to substrate infilling in remediated habitats. Material presented in this review will help align sturgeon research and monitoring approaches in support of effective remediation. The limited number of remediation projects to‐date attests to the importance of learning from existing projects and cross‐species comparisons, to maximize the effectiveness of future restoration efforts.

Characterization of Pallid Sturgeon ( Scaphirhynchus albus ) Spawning Habitat in the Lower Missouri River

“…Very little design guidance exists for functional spawning habitat in the LMOR. Spawning habitat construction and remediation efforts, particularly for lake sturgeon, have shown variable rates of success (McAdam et al, ). It is unclear the extent these rehabilitation efforts translate to LMOR and to pallid sturgeon, although there is value in lessons to be learned from less successful or failed restoration projects (Baril, Biron, & Grant, ).…”

“…Sturgeon have been documented spawning over gravel, cobbles, boulders, bedrock, sand, and artificial substrates such as wood pilings, often immediately downstream from a dam (Bruch & Binkowski, ; Du et al, ; Krykhtin & Svirskii, ; Paragamian, ; Parsley, Beckman, & McCabe, ; Sulak & Clugston, ). Spawning habitat hydraulics vary with species and river system; however, many sturgeon species commonly aggregate and spawn in habitat patches with a wide range of depths and relatively high flow velocity (Baril, Buszkiewicz, Biron, Phelps, & Grant, ; McAdam et al, ; Smith, Smokorowski, & Power, ; Wyman et al, ). Sturgeon eggs become adhesive several minutes after fertilization and the common inference is that functional spawning substrate for pallid sturgeon is also likely coarse, hard, rock material which allows for stability in high‐velocity environments where currents prevent sedimentation (Detlaff, Ginsburg, & Schmallhausen, ; Laustrup, Jacobson, & Simpkins, ).…”

“…In high‐velocity environments, fertilized eggs may be transported some distance downstream before adhering to coarse substrates or being entrained in interstitial spaces. Lack of knowledge of specific habitat conditions necessary for successful spawning and reproduction of pallid sturgeon limits the ability to define conservation or engineering criteria for habitat protection and rehabilitation efforts (Baril et al, ; McAdam et al, ; Wang, Xia, & Wang, ).…”

Observations regarding Lake Sturgeon spawning below a hydroelectric generating station on a large river based on egg deposition studies

“…For thousands of years, high velocity torrents capable of dispersing recently spawned Lake Sturgeon eggs over a large area (relative to the extent of dispersal in a low-flow environment) have emanated from features such as falls/rapids, which are common along Boreal Shield rivers. Deposition and/or accumulation of fine particles, such as clay and silt, which have been reasoned problematic in the context of spawning habitat enhancement initiatives in non-Boreal Shield rivers (Johnson et al, 2006;McAdam et al, 2017), would largely be precluded in these areas. Flow facilitated egg dispersal over a large area (and a diversity of hard substrates) would limit "layering" of eggs, as observed contemporarily in the Wolf River (Bruch & Binkowski, 2002).…”

Juvenile lake sturgeon monitoring and determinants of year‐class strength in the Rupert River, mid‐northern Québec, Canada

“…To minimize the project's impacts in the river's reduced‐flow section, an instream flow regime was implemented in fall 2009 to maintain the quality and quantity of available spawning habitat areas for several species, including lake sturgeon (McAdam et al, ). The instream flows help preserve the spawning grounds and promotes successful spawning in both spring and fall.…”