Review Reports

Round 1

Reviewer 1 Report

A welcome topic, an original and useful approach from the  Back-Calculation approach point of view, different from what others Back-Calculation Methods has been done so far. The article respects the rigors of a scientific paper.

The sections  Abstract, Introduction, Material and Methods, Results, Conclusion  and contain clear analyses, explanations, corelations and conclusion  reflecting nature and  inter- conditionalities.

Bibliographic resources are correctly mentioned throughout the article.

Reviewer 2 Report

In this work Renato et al. states the impact of invasive species Silurus glanis on the local ichthyofaunal diversity and, mainly, proposes a novel indicator using undigested ( focusing on vertebrae) prey parts by the Eurasian otter Lutra lutra. 

The work is clear and well written and indeed adds value to the current literature, however a few details require clarification.

Line 70 Please state the methodology of electrofishing as well as the device used

Line 152 " they represented useful tools for species identification " It is a known fact, please use citation

Hopefully, in time, the K index will become one of the classic indicators. Good work, congratulation.