can be used as general size bars for fish length determination. AUTOMATED AND COLORIMETRIC CALIBRATED VIDEO-IMAGING PROTOCOL FOR THE DAY-NIGHT COUNTING OF FISHES AT A CABLED OBSERVATORY

Abstract: We describe a new automated and colorimetric calibrated video-imaging protocol for the 24-h continuous counting of fishes. Images of approximately 2 x 2 m methacrylate red panel with a chromatic chart were acquired at 30 min frequency with the cabled observatory OBSEA (www.obsea. es), installed at 20 m depth off Vilanova (Spain). The spectral reflectance value for each patch was measured between 400 to 700 nm and then converted in standard RGB, and used as a reference for all following calibrations. All image analysis was carried out within a standardized Region Of Interest, using the recently implemented “3D Thin-Plate Spline ” warping approach. That operation was repeated on a subset of 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 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