title: A new colorimetrically-calibrated automated video-imaging protocol for day-night fish counting at the OBSEA coastal cabled observatory.
abstract: Field measurements of the swimming activity rhythms of fishes are scant due to the difficulty of counting individuals at a high frequency over a long period of time. Cabled observatory video monitoring allows such a sampling at a high frequency over unlimited periods of time. Unfortunately, automation for the extraction of biological information (i.e., animals' visual counts per unit of time) is still a major bottleneck. In this study, we describe a new automated video-imaging protocol for the 24-h continuous counting of fishes in colorimetrically calibrated time-lapse photographic outputs, taken by a shallow water (20 m depth) cabled video-platform, the OBSEA. The spectral reflectance value for each patch was measured between 400 to 700 nm and then converted into standard RGB, used as a reference for all subsequent calibrations. All the images were acquired within a standardized Region Of Interest (ROI), represented by a 2 × 2 m methacrylate panel, endowed with a 9-colour calibration chart, and calibrated using the recently implemented "3D Thin-Plate Spline" warping approach in order to numerically define color by its coordinates in n-dimensional space. That operation was repeated on a subset of images, 500 images as a training set, manually selected since acquired under optimum visibility conditions. All images plus those for the training set were ordered together through Principal Component Analysis allowing the selection of 614 images (67.6%) out of 908 as a total corresponding to 18 days (at 30 min frequency). The Roberts operator (used in image processing and computer vision for edge detection) was used to highlights regions of high spatial colour gradient corresponding to fishes' bodies. Time series in manual and visual counts were compared together for efficiency evaluation. Periodogram and waveform analysis outputs provided very similar results, although quantified parameters in relation to the strength of respective rhythms were different. Results indicate that automation efficiency is limited by optimum visibility conditions. Data sets from manual counting present the larger day-night fluctuations in comparison to those derived from automation. This comparison indicates that the automation protocol subestimate fish numbers but it is anyway suitable for the study of community activity rhythms.
authors.affiliation: SARTI Research Group, Electronics Department, Universitat Politècnica de Catalunya (UPC), Rambla de la Exposición 24, Vilanova i la Geltrú-Barcelona 08800, Spain. joaquin.del.rio@upc.edu.
authors.forename: Joaquín
authors.initials: J
authors.lastname: del Río
authors.forename: Jacopo
authors.initials: J
authors.lastname: Aguzzi
authors.forename: Corrado
authors.initials: C
authors.lastname: Costa
authors.forename: Paolo
authors.initials: P
authors.lastname: Menesatti
authors.forename: Valerio
authors.initials: V
authors.lastname: Sbragaglia
authors.forename: Marc
authors.initials: M
authors.lastname: Nogueras
authors.forename: Francesc
authors.initials: F
authors.lastname: Sarda
authors.forename: Antoni
authors.initials: A
authors.lastname: Manuèl
mesh_terms: D000818:Animals; D003124:Colorimetry / Q000295:instrumentation / Q000379:methods*; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D005399:Fishes / Q000502:physiology*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D025341:Principal Component Analysis; D014741:Video Recording / Q000295:instrumentation / Q000379:methods*