Shelter is a crucial component to many species' survival, and when shelter becomes limited, resulting competition can have negative effects on growth and survival. In Little Chucky Creek, a tributary to the Nolichucky River in Tennessee, the severe population decline of the Chucky Madtom Noturus crypticus has been partially attributed to an increase in the abundance of cavity-dwelling crayfish following the establishment of two nonnative species. While it has been suggested that the crayfish exclude the cavity-dwelling fish from shelter, we are not aware of studies that have been conducted to demonstrate that crayfish directly outcompete madtoms in this regard. Our objective was to experimentally test the hypothesis that shelter competition between crayfish and the Mountain Madtom N. eleutherus, a surrogate species for the Chucky Madtom, is a function of relative size. Behavioral trials were conducted in which shelter was the limited resource for the two potential competitors. The madtoms' success at occupying the provided cover object was recorded for 5 days as well as health condition at the end of the competition phase. Both madtom occupancy and health condition were positively correlated with increasing relative size. As the size differential increased between madtoms and crayfish, madtoms were more successful at occupying the cover object, and overall condition was greater at the end of the trial. Conversely, when madtoms were smaller than crayfish, individuals were more commonly excluded from the cover object or even killed. Juvenile madtoms experienced 100% mortality. We concluded that crayfish exhibit a size-specific competitive advantage over Mountain Madtoms when shelter is limited, and that crayfishes may catalyze fish population declines at least partially through shelter exclusion and predation on juveniles.

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The freshwater mussel fauna of the Barren River system in Kentucky is well documented, but information on mussel occurrence in the Tennessee portion of the system was lacking. We conducted mussel surveys at 56 sites in 22 streams in the Barren River system in Tennessee. We found six species at 14 sites: Alasmidonta viridis (Slippershell), Fusconaia flava (Wabash Pigtoe), Lampsilis cardium (Plain Pocketbook), Lampsilis siliquoidea (Fatmucket), Pyganodon grandis (Giant Floater), and Villosa ortmanni (Kentucky Creekshell). Our records of V. ortmanni are the first reports of this species from Tennessee, and our records of L. siliquoidea considerably expand the known range of that species in the state. We found live or freshly dead V. ortmanni at five sites, and at least two sites supported relatively large populations with evidence of recent recruitment. These observations represent important information for the conservation of this imperiled species. Overall, mussel populations in the Barren River system of Tennessee were small and scattered, which may be due, in part, to the lower mussel abundance typical of headwater streams. However, the occurrence of widespread mussel declines in this region suggests that human factors may have further reduced mussel abundance.