Meeting Abstract
Eye size and shape are important for determining the significance of vision to both individuals and to species whereby large eyes have greater resolution and sensitivity. Within an individual, eye growth is metabolically costly, suggesting that large eyes play a larger role in the ecology of an animal. Vision can also provide insight into prey selection, predator and mate detection capabilities, and habitat utilization. For example, elasmobranchs demonstrate a variety of pupil morphologies including vertical and horizontal slits, pinholes, and crescents. Pupil shape is correlated to an organism’s environmental light level and time of day it is most active. Although some studies have investigated eye and pupil shape in select elasmobranch species, less is known regarding eye and pupil shape on a broader scale. Eye size, eye shape, and pupil shape of seven coastal elasmobranchs from the southeastern United States were quantified using photographic analyses: Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus), finetooth (Carcharhinus isodon), dusky (Carcharhinus obscurus), sandbar (Carcharhinus plumbeus), scalloped hammerhead (Sphyrna lewini), and bonnethead (Sphyrna tiburo). All species had round eyes with vertical slit pupils, with the exception of the hammerheads (Sphyrna spp.), which possessed slightly oblong eyes with horizontal pupils. As benthic feeders, a horizontal pupil reflects their plane of vision while foraging. Scalloped hammerheads had the largest eye size relative to their body length. Because visual sensitivity positively scales with eye size, scaling should also be considered in future analyses.
