Riassunto analitico
Little information is available on the decomposition of bodies in freshwater systems, yet the study of decay in this type of environment is important for the estimation of the mPMI, the PMSI and the manner of death. In previous experiments, the importance of Procambarus clarkii in the consumption of dead bodies in freshwater ponds in Northern Italy was assessed. This crayfish, native of Southern USA, recently spread in Europe after its introduction for aquaculture.
The present study aimed at characterizing the role of P.clarkii in the decomposition of carcasses in freshwater systems by studying the population dynamics in relation to the decomposition stage and the wounds caused by the crayfish’s feeding activity. The study was conducted in Nonantola (MO), Northern Italy, and it consisted in four experiments, the first in July, the second in August-September, the third from November to June, the fourth in June-July. Five pig carcasses (Sus scrofa) enclosed in lobster pots were placed in different positions inside an artificial freshwater dew pond. The number of P.clarkii detected on each carcass was recorded following a fixed sampling protocol, together with the type and outline of the wounds caused by the crayfish’s feeding activity on the carcasses, the water level and meteorological data.
Results show that in the non-winter experiments, the Crustaceans attacked the carcasses a few hours after their positioning, starting to damage the external epidermal layer with lacerations up to 4cm, generally ascribable to round shape wounds. The initial day of deposition of the body inside the pond corresponded with the first peak in P.clarkii population with up to 100 specimens detected in each lobster pot. In the following days, the crayfishes continued their activity, increasing the percentage of damaged skin until the full laceration of the dermal layer. The second peak in crayfish’s population occurred after the end of the floating decay stage, with the carcass lying again on the bottom of the pond; this peak could be explained with the low swimming ability of the crayfish. From that moment, the feeding activity continued mostly in the internal part of the carcass, with the attack to the internal organs, until the flesh was completely consumed by the crustaceans and only bones remained. The situation was different in the winter experiment: crayfish colonised the carcasses from the first day after pigs positioning in water, but the decomposition carried on slowly. The crayfish feeding activity was lesser and because of this and the low water temperatures, the skeletisation occurred only after seven months.
This study shows that the feeding activity of P.clarkii is crucial in the dismemberment of bodies in freshwater and the importance in the forensic field is on two main points. On one side, by detecting differences in the colonisation of the body in relation to the season and the position in the water column, these results are useful for the estimation of the mPMI interval of bodies found in freshwater systems. On the other side, it emerged that the typical shape of the wounds made by the Crustaceans could be confused for sharp force injuries which could lead to a wrong report on the causes of death.
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