Is Shallow Water a Suitable Surrogate for Assessing Efforts to Address Pallid Sturgeon Population Declines?

It is hypothesized that slow, shallow water habitats benefit larval pallid sturgeon Scaphirhynchus albus; however, testing this hypothesis is difficult, given the low number of larval pallid sturgeon present in large rivers. In contrast, relatively large numbers of age-0 shovelnose sturgeon Scaphirhynchus platorynchus have been sampled, providing a potentially useful baseline to assess the importance of slow, shallow water to age-0 sturgeon of both species (hereafter age-0 sturgeon) in the lower Missouri River. Thus, we investigated the potential relationships between the prevalence of shallow water <1.5m and the age-0 sturgeon catch rates at multiple scales. Age-0 sturgeon were usually sampled in water >1.5m, and catch rates were usually highest in the upper half [i.e. river kilometre (RKM) 400 to 800] of the lower Missouri River study area, whereas the availability of water <1.5m was usually highest in the lower half (i.e. RKM 0 to 400). Similarly, there was no relationship between age-0 sturgeon mean catch-per-unit effort and ha/km of water <1.5m at any studied scale. Our results may suggest that shallow water, as currently defined, may not be a suitable surrogate for assessing efforts to address pallid sturgeon population declines. However, it is still unknown if lack of appropriate habitat is currently limiting pallid sturgeon. Published 2015. This article is a U.S. Government work and is in the public domain in the USA. River Research and Applications published by John Wiley & Sons Ltd.