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Comparison of Two Stereo-Video Software for the Assessment of Marine Resources

Abstract:

In the last two decades underwater stereo-video analyses have received interest for use in diversity, abundance, and biomass estimations for marine species because of their low-cost, time-efficient and as a not invasive technique. Here, we assessed the accuracy and precision of measurements from two videogrammetric software (VidSync and EventMeasure by SeaGIS) from a Baited Remote Underwater Stereo-Video system (Stereo-BRUVs) for determining the size of objects of known length under controlled conditions and lengths of pelagic fish in open ocean conditions. One Stereo-BRUVs equipped with GoPro cameras was employed to take measurements of known-length rods in a pool to compare the influence of size, distance to rod and angle to the optical axis on measurement accuracy and precision. The ability to estimate fish length in open waters was tested by measuring 14 individuals of the common dolphinfish (Coryphaena hippurus) with the same Stereo-BRUVs equipment simultaneously calibrated for both software. The pool test showed that SeaGIS measurements (error = 0.22%) were more accurate than VidSync (error = 0.63%) only for the shortest rod. For both software, accuracy remained high (> 99%) and did not decrease regardless the size, distance, and angle of the measured rods. The open waters measurements showed high correlation (R2 = 0.99) between VidSync and SeaGIS for the common dolphinfish, suggesting that both software take similar measurements of individual fish. We suggest both software make length estimations with great accuracy and precision.