It’s a Trap! An evaluation of different passive trap types to effectively catch and control the invasive red swamp crayfish (Procambarus clarkii) in streams of the Santa Monica Mountains

Abstract

The invasive red swamp crayfish poses a significant threat to physical habitat quality and biodiversity of aquatic communities in western U.S. streams. With no natural predators or competitors, crayfish can consume adult, juvenile, and egg forms of native fish, amphibians, and benthic macroinvertebrates. In addition, crayfish can destroy physical structures and disrupt nutrient and sediment dynamics by burrowing into banks and increasing turbidity. Mountain Restoration Trust has managed crayfish populations in the Santa Monica Mountains for almost a decade, yet evaluation of trap type effectiveness has remained a constant source of uncertainty in overall management efforts. In this two-week field experiment, we compared 12 trap designs including refuge traps, baited pyramid traps, and baited minnow traps with different colors and opening sizes to determine which traps caught the most crayfish and least bycatch. There were significant differences observed across the traps tested in the number of crayfish, chub, and tadpoles caught. The most effective trap for catching crayfish were both mesh traps, the Promar mesh 503 trap (mean daily crayfish catch = 1.9, SE = 0.24) and the Promar mesh 501 trap (mean daily crayfish catch = 1.2, SE = 0.26). The least effective traps, that caught more bycatch than crayfish, were the painted-black Gee Minnow trap (mean daily chub bycatch = 3.3, SE = 0.98) and the customized Pyramid trap with 5.1 cm openings (mean daily chub bycatch = 3.2, SE = 1.30). When managing for crayfish in southern California, arid-environment streams, we recommend deploying a combination of the Promar mesh 503 trap, the Promar mesh 501 trap, and/or the black Promar (2.5 cm). The combination of these traps can maximize crayfish catch efficiency and limit negative impacts on native fish and tadpole bycatch.