An open source tool for echogram visualization and analysis

Scrutiny and analysis of multi-frequency digital echograms are the basis of modern fisheries acoustics biomass estimations. Currently, several data formats and dedicated software exists for this purpose, however commercial options tends to be expensive. Moreover, acoustic analysis is complex, and besides the acoustic data itself, it also requires other types of information (species composition and fish lengths from identification fishing hauls, physical environment data like CTD casts, sea surface temperature, etc.), making a flexible and powerful computing environment greatly appreciated. R provides such an environment, with its programming tools, statistical procedures available, mapping functions and data processing in general. Here we describe 'echogram' an R package capable of importing the hydroacoustic data file format for producing echogram visualizations with predefined or custom color palettes; modelling and subtracting background noise; and more important, develop and test acoustic filtering algorithms useful in biological scatterers discrimination, by combining different acoustic frequencies. Being an open source tool, interested users can participate in the development of the package by improving existing functions and extending its functionality by adding new ones.