Status and Habitat Patch Use of Scaphirhynchus Sturgeon in An Important Fluvial Corridor

Identifying the habitat template that will facilitate the recovery of imperiled fishes is a challenging task, particularly for species that are sparsely distributed in environments that are difficult to sample.  Nevertheless, it is important to regularly assess the status and habitat use of imperiled species to direct or redirect conservation efforts.  The goals of this study were to: 1) assess the status of the federally endangered pallid sturgeon and its congener, the shovelnose sturgeon, using a mark-recapture protocol and 2) to identify sturgeon habitat patch use, analyzed using a regression tree approach.  This study was conducted on the middle Mississippi River (MMR), which is an important fluvial corridor (approximately 309 km) that connects the upper Mississippi River and Missouri River basins with the lower Mississippi River basin.  Data were collected from the MMR over a four-year period using gillnets, trawls, and trotlines.  Our population estimates from mark-recapture analyses were 1,516 pallid sturgeon and 82,336 shovelnose sturgeon.  This equates to approximately 5 pallid sturgeon and 266 shovelnose sturgeon per river kilometer.  Regression tree analyses indicated that sturgeon abundance was highest at the downstream ends of islands (among 10 habitat patch types).  The population estimates highlight the critical status of the pallid sturgeon.  Though the shovelnose sturgeon has been the target of past roe fisheries, it appears to be fairing comparatively well to the pallid sturgeon.  We conclude that island restoration is a realistic goal to facilitate the recovery of sturgeon in, and perhaps beyond, the MMR.