Visual field of the bottlenose dolphin (Tursiops truncatus)
Abstract
Field of vision (FOV) aids a marine mammal in locating an object and the blind spot within the FOV can impede this ability, possibly leading to harm such as boat strikes (Murayama & Somiya, 1998; Wells et al., 2008). Identifying the FOV of bottlenose dolphins (Tursiops truncatus) is an important, but difficult question to study in cetacean biology. Previous attempts have examined the eyes of dead animals to generate potential FOV data based on retinal blind spots (Murayama & Somiya, 1998). But despite a large body of knowledge on vision in some mammals, little is known about bottlenose dolphins' 'practical FOV', defined as the FOV determined from live animals using psychophysical methods. I hypothesized that bottlenose dolphins have blind spots due to selection pressures associated with being both predator and prey in a three-dimensional fluid environment. I predicted blind spots occur in the area along the dorsal fin based on previous research indicating a high number of injuries to this back dorsal area (Wells et al., 2008). I also tested the claims that dolphins cannot see in the frontal area of the rostrum (Starkhammar et al., 2007; Xitco et al., 2004). The primary goal of this study was to determine the practical FOV in bottlenose dolphins and to identify the blind spots using a two-step approach. First, three dolphins from Dolphin Quest: Bermuda were psychophysically trained to give positive acoustic signals to the presence of light stimuli. Second, psychophysical training methods were used to map the dolphins' FOV and determine the location of blind spots in dolphin vision using LED lights at 25 different junction points in a Hoberman sphere, a geodesic dome structure large enough to encompass a dolphin's head (Li et al., 2018). As a result, the three dolphin subjects were able to see anteriorly, but were unable to see in the back dorsal area, which signifies that my hypothesis was supported and the claims made by Starkhammar et al. (2007) and Xitco et al. (2004) were not supported. The knowledge obtained has expanded our comparative understanding of mammalian eye evolution and contributes to conservation applications.
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- OSU Theses [15752]