Crayfish Use of Trash Versus Natural Cover in Incised, Sand-Bed Streams

Abstract

Historic land use changes and subsequent river channelization created deeply incised, unstable stream channels largely devoid of natural cover throughout the Yazoo River basin, Mississippi, USA. Large trash (e.g., televisions, toilets, car parts) dumped in streams provided shelter for some aquatic fauna. To determine whether trash served as a surrogate for natural cover, I examined crayfish use of both cover types. I sampled crayfishes by kickseining 2 9 1-m plots in three cover classes: trash, natural cover, and no cover. I captured 415 crayfishes from 136 of the 294 plots. Most crayfishes were in natural cover (253), followed by trash (154), and no-cover (8) plots. Trash use varied by crayfish genus and size. Frequencies of all size classes of Procambarus and of the smallest Cambarus were higher in natural cover than trash. Many of the smallest individuals were found in live root mats. As Cambarus and Orconectes grew, they shifted more toward trash, and the largest Orconectes size class was significantly more abundant than expected in trash. Trash served as ''artificial reefs,'' providing cover for crayfishes and other fauna, but functioned differently than the remaining natural cover. The results confirmed that stream substrate did not provide adequate instream cover for crayfishes in the study area and suggested that high-quality natural cover for large crayfishes was in short supply, at least for some species. Land management that provides for abundant, ongoing input and retention of complex cover, such as trees and live roots, to stream channels should be beneficial for crayfish assemblages.

Review of Dam Effects on Native and Invasive Crayfishes Illustrates Complex Choices for Conservation Planning

“…These processes can lead to even small streams being deeply entrenched and incised, a common occurrence in the Coastal Plain of the southeastern US (Patrick et al, 1991;Hartfield, 1993). While the effects of such incision on crayfishes are poorly studied, incised streams are marked by flashy hydrographs, extremely unstable substrates, and a paucity of instream cover, all of which seem to translate to reduced crayfish densities (Adams, 2014). Dams can retard upstream channel incision, thereby helping to minimize stream headcutting and retain instream cover and stream interactions with their floodplains in ways that should benefit crayfish assemblages.…”