Measurements of juvenile Atlantic bluefin tuna (Thunnus thynnus) size using an unmanned aerial system

An APH-22 vertical-takeoff-and-landing hexacopter was used to collect aerial images of schools and individuals of juvenile Atlantic bluefin tuna (ABET; Thunnus thynnus) at the sea surface in the southern Gulf of Maine. Quantitative measures of fish length, width, and inter-fish spacing were obtained from these images by applying calibration settings and performance measures from calibrating, testing, and evaluating the onboard motion and altimeter sensors and the digital camera and lenses. The accuracy and precision of the onboard motion sensors, camera, and lens calibrations were sufficient to provide length measurements to sub-centimeter precision, but the altimeter performance was least reliable and required additional information, such as images of known-sized objects during each flight, to provide measurements at the accuracy and precision needed for data to be incorporated in fisheries management. The APH-22 was ideal for acquiring images of ABET individuals and schools and may be a useful tool for remotely monitoring the behavior and body condition of these elusive animals.