Trashy Accommodations: Where Crayfish Dwell When Cover Is Limited Due to Historic Land Use Practices

Extensive, historic clear-cutting throughout the Yazoo River basin, Mississippi, USA, and subsequent river channelization created deeply incised, unstable stream channels largely devoid of natural cover.  Existing anthropogenic cover provided an opportunity to examine the use of supplemental shelter by crayfishes and to make inferences about shelter limitation in these sand-bed streams.  An astonishing array of large trash (e.g., televisions, toilets, tires) in some streams potentially provided important cover for aquatic fauna. I examined crayfish use of trash versus natural cover and open habitats.  I used kick seining to sample equal numbers of 1 x 2 m plots in each of three stream microhabitat types: garbage, natural cover, and no cover.  Garbage toxicity was not tested.  I captured 413 crayfish from 136 of 294 seine hauls.  The most crayfishes were in natural cover (253), followed by garbage (152), and no-cover habitats (8).  Six of the seven species captured had equal or higher abundances in natural cover compared to garbage.  Crayfish size distribution was unequal among the 3 cover types. Habitats lacking cover had the largest crayfish median size because they did not contain small juveniles.  Habitats with garbage had the largest crayfishes; of the largest 5% of crayfish captured, 65% were collected from garbage.  Large garbage functioned as artificial reefs, providing cover for crayfishes as well as fishes and reptiles, until the garbage became embedded with sand.  Some garbage also retained woody debris and leaf litter.  The results suggest that natural cover is limiting in the streams, especially for the largest crayfish, and may help explain the negative species-area relationship for crayfishes in the basin.  Contemporary land management practices cannot reverse the channel incision, although secondary flood plains may develop within stabilized, incised channels.  Land management that provides for abundant and ongoing inputs of cover such as large or live wood to stream channels should be beneficial for crayfishes.  Conversely, management that reduces sources of instream cover or increases peak storm flows, thereby contributing to destabilization of channels and cover, will be detrimental.