State of the ART: Using artificial refuge traps to control invasive crayfish in southern California streams

Invasive species are a widespread threat to stream ecosystems across the planet. In Southern California, USA, the invasive red swamp crayfish Procambarus clarkii (Girard, 1852) poses a significant threat to native aquatic fauna. Studies have suggested that artificial refuge traps (ARTs) resembling crayfish burrows can be used to remove invasive crayfish, but, to date, no studies have focused on optimizing ART design and deployment to maximize crayfish catch. This month-long study tested the effect of modifications on ART diameter, color, and soak time on P. clarkii catch effectiveness across 160 traps. We evaluated catch data by creating multiple candidate generalized linear mixed models predicting P. clarkii catches with different modeling parameterizations and a priori hypothesized predictor variables. During the study period, ARTs removed a total of 240 red swamp crayfish with no incidental bycatch. Larger P. clarkii (2-6-cm carapace length) were found more frequently in 5.1-cm-diameter traps, and smaller P. clarkii (1-4 cm) were found more frequently in 2.5-cm-diameter traps. Catch numbers varied between trap types, with black-colored 5.1-cm-diameter traps removing the greatest amount of the total P. clarkii caught in the study (mean = 0.27, SD = 0.29; 35% of the total caught) and black-colored 2.5-cm-diameter traps removing the least amount (mean = 0.09, SD = 0.55; 12% of the total). Further, ART deployment duration was an important predictor variable for candidate models, where ARTs with 4-d and 7-d deployment durations had lower catch/unit effort than traps with 1-d and 2-d deployments. This factorial experiment is the 1st study to suggest specific design modifications to ARTs that optimize invasive red swamp crayfish removal without incurring non-target incidental bycatch. This study demonstrates that ARTs can be a valuable tool for conservation managers interested in restoring streams through invasive crayfish removal, especially where there are sensitive biological resources.