Population structure and dynamics of the invasive Procambarus clarkii (Girard, 1852) in a Tiber river Ramsar site, Central Italy

Procambarus clarkii is a native species of central America, but strongly invasive in many regions of the world. An investigation on the red swamp crayfish was carried out to obtain more information about its population dynamics in the Tiber River, in central Italy. A total of 900 individuals, both males and females, were sampled within two different campaigns (2017 and 2019) aimed at collecting biometric data. A strong fishing effort was deployed (more than 100 nets set), to guarantee a large and randomized number of samples. The crayfish populations were grouped into seven different cohorts, according to Bhattacharya’s method. The population showed a balanced sex ratio, the average cephalothorax length was 42.52 mm, with the most represented size class between 40-50 mm. K and L∞, as well as the growth parameter index (Ø), the mortality rate (Z), and longevity value (tmax), were calculated. K and Ø values resulted very high, showing an impressive growth rate in the study area; tmax ranged from 4 to 5 years, L∞ values were lower compared with other studies (58.0-59.0 mm), while Z was very high for this population (4.2-4.5 year). The results revealed that crayfish population dynamics can be complex and vary depending on habitat type, available trophic resource and competition.