Crayfish are an economically and ecologically important invertebrate, however, research on crayfish in their native habitats is patchy at best. Research in Florida is sparse, even though the Southeastern U.S. is known to be one of the most speciose globally. This study investigated patterns of abundance and habitat distribution of two crayfishes (Procambarus fallax and P. paeninsulanus) in two of Florida first magnitude spring-fed rivers (Wakulla River and Silver River, respectively). The study sites were surveyed once in each of four seasons from April 2015 to March 2016. Baited minnow traps were deployed and checked every other day, four times, at 50 sites in each river, covering approximately eight kilometers of each river. Habitat and environmental data was collected at each site during each survey, including submerged and emergent vegetation, percent cover, organic matter content of sediment, dissolved oxygen, temperature, water depth, lunar phase and categories of human access. Abundance was estimated using N-mixture models and a model selection approach was used to judge the relative evidence between hypotheses relating covariates to crayfish abundance. Final inference was based on a Bayesian hierarchical model to obtain better estimates of parameters and their precision.
Results/Conclusions
P. fallax was identified in the Silver River (first apparent identification of crayfish in this river) and P. paeninsulanus was identified in the Wakulla River, confirming previous identification in gray literature. Abundance and detection of P. fallax was lower than P. paeninsulanus (for example, from the Fall survey, abundance of 11 with CI: 4 – 30 crayfish/site versus 17 with CI: 10 – 29 crayfish/site and detection of 1.94 percent with CI: 0.84 – 4.78 versus 15.98 percent with CI: 9.54 – 25.55, respectively). Abundances of both species vary with types of vegetation and percent organic matter of the sediment. In addition, abundance of P. paeninsulanus varied with anthropogenic disturbance within the study area of the river. Data provided by this study on crayfish population dynamics and habitat use and distribution will assist State Park Managers with understanding potential impact from herbicidal control of Hydrilla verticillata, a species invading these rivers. In addition, this study will fill knowledge gaps on Florida crayfish natural history and ecology, including identification of the species in the Silver River for the first time.