Aerial Videogrammetry From a Tethered Airship to Assess Manatee Life‐stage Structure

Abstract

Aerial videogrammetry from an airship tethered to a boat was used to assess the life‐stage structure of manatees in the Blue Waters area of the Homosassa River on the west coast of central Florida. Individual frames of videos were loaded onto a computer and lengths of manatees measured using graphics software. All images of manatees were measured independently by three observers. Measurements were transformed to total manatee lengths by calculating the ratio between the measurements of a reference object of known length and the measurement of the manatee. Length estimates were highly variable but were unbiased with respect to observer. Results of an analysis of variance suggested that the hypothesis that lengths differed among days and among observers should not be rejected. Life‐stage structures were represented in three schemes. One scheme‐which included four life stages: dependent calves, juveniles, animals in tramsition between juvenile and adult, and adults‐was included to provide the most information without sacrificing confidence in the life‐stage distribution. Overall, the video system was effective at capturing images of manatees for life‐stage characterization and, with improvements in image resolution, could become a valuable tool for photo‐identification in sight‐resight experiments.

The Use of Unmanned Aerial Systems in Marine Mammal Research

“…The idea of combining boat observation with aerial imagery for marine mammal behavior surveys is not new. In the early 2000s, several studies on manatees (Trichechus manatus latirostris) and bottlenose dolphins were conducted using a video camera mounted on a tethered, helium-filled aerostat, also called a "blimp" [56][57][58][59]. This approach highlighted the possibility of following the animals during the time spent underwater, depending on depth and water turbidity [57,58].…”

Wildlife research and management methods in the 21st century: Where do unmanned aircraft fit in?

“…The earliest accounts of aquatic mammal observation using UAS involved tethered airship systems. Flamm et al (2000) used such a system equipped with a video camera to measure the length of manatees (Trichechus manatus) congregating in Homosassa River, Florida, while Nowacek et al (2001aNowacek et al ( , 2001b used a similar system to monitor the responses of bottlenose dolphins (Tursiops truncatus) to boat traffic in Sarasota Bay, Florida.…”

A simple laser photogrammetry technique for measuring Hector's dolphins (Cephalorhynchus hectori) in the field

“…Single camera photogrammetry requires either a known object in the image for scale ( e.g. , Best and Rüther 1992, Flamm et al 2000) or a measurement of the range to the individual ( e.g. , Gordon 1991, Spitz et al 2000, Jaquet 2006).…”