Meeting Abstract
Visual function in the high-performance and regionally endothermic sharks is assumed to be superior to that of their ectothermic counterparts. These migratory lamnid species, including the white shark (Carcharodon carcharias) and the shortfin mako (Isurus oxyrinchus), are thought to be visually guided predators with eyes adapted to a wide range of visual habitats. Though shark vision has been of interest to researchers for several decades, most studies are limited to smaller, more accessible species. More recently, greater access to large, predatory species enables us to address outstanding questions regarding the role of vision with respect to their life history traits. To examine visual performance of the white shark and the shortfin mako, we used a visual range model developed by Nilsson et al. (2012). The input parameters included measurements of pupil diameter and focal length, photoreceptor length and peak retinal ganglion cell density, light level, and target size and contrast. Pupil diameter and focal length were measured from incidental mortalities and photographs of live specimens, whereas photoreceptor length and retinal ganglion cell data were taken from previously published data. For sharks viewing a human diver in a black wetsuit in clear, oceanic water, we calculated a visual range of approximately 20m, similar to human vision under the same conditions. However, shark vision is coarser than humans, so less detail is available to sharks for identifying objects using their visual system. Because eye size positively correlates with both sensitivity and acuity, further investigation across both species size ranges will address the functional significance of the visual system with respect to ecological patterns.
