Habitat distribution and abundance of crayfishes in two Florida spring-fed rivers

Crayfish are an economically and ecologically important invertebrate, however, research on crayfish in native habitats is patchy at best, including in Florida, even though the Southeastern U.S. is one of the most speciose areas globally. This study investigated patterns of abundance and habitat distribution of two crayfishes (Procambarus paeninsulanus and P. fallax) in two Florida spring-fed rivers (Wakulla River and Silver River, respectively). Study sites were surveyed once each season from April 2015 to March 2016 with baited minnow traps checked every other day, four times each survey. Habitat and environmental parameters evaluated included dominant vegetation or bottom type, percent cover, organic matter content, water depth, moon illumination and dissolved oxygen. Abundance was estimated with N-mixture models. Model selection judged the relative evidence between hypotheses relating habitat and environmental covariates to crayfish abundance. P. paeninsulanus distribution and abundance in Wakulla River was explained by time of year, dissolved oxygen and dominant bottom and vegetation type. P. fallax distribution and abundance in Silver River was explained by time of year and percent coverage of vegetation. Detection of P. paeninsulanus was higher than P. fallax and abundance of P. paeninsulanus was more heterogenous than P. fallax (6-18 versus 12-14 per site in summer survey). Distribution of P. paeninsulanus as described by vegetation and bottom type also seems to follow heterogeneity in management areas in Wakulla River. Results will assist managers in understanding potential impact of herbicidal control of Hydrilla verticillata on crayfish. This study also fills knowledge gaps on Florida crayfish natural history and ecology