Energetic Costs Associated with Habitat Use during Early Life Influence Growth Rate Potential of Scaphirhynchus Sturgeon

The endangered pallid Scaphirhynchus albus and shovelnose sturgeon S. platorynchus are fluvial specialists that occupy heterogeneous flow fields within large, sand-dominated river ecosystems.  Research suggests both species select sand over gravel, but the energetic costs of occupying such microhabitats is unknown.  We used intermittent, flow-through respirometry to quantify energy expenditure (MO₂; mg O₂ kg^-1 h^-1) of age-0 pallid and shovelnose on sand and gravel at velocities of 15 cm s^-1 and 30 cm s^-1.  Experimental results were incorporated into a bioenergetics model of growth rate potential to consider how physical variables in a defined habitat affected a hypothetical sturgeon’s energy budget. In the experiment, MO₂ was higher over sand substrate for both species. The difference in MO₂ between sand and gravel for pallid sturgeon was less than shovelnose sturgeon, which suggests segregation may occur where sturgeon overlap within microhabitats. Velocity did not affect MO₂. Our model provided a value of habitat quality for age-0 sturgeon within different microhabitat types and allowed us to examine whether the benefits of occupying sand outweigh the increased cost of station holding. Microhabitat composition and food availability may be primary drivers of habitat selection for age-0 sturgeon.