Meeting Abstract

57.1  Tuesday, Jan. 5  Visual and electrosensory integration in hammerhead sharks KAJIURA, Stephen M*; MCCOMB, D Michelle; Florida Atlantic University kajiura@fau.edu

The unique head morphology of hammerhead sharks (Family Sphyrnidae) provides a dorsal ventrally compressed and laterally expanded platform upon which sensory structures are distributed. The spatial distribution of sensors dictates how the sharks perceive their environment. This study examined the consequences of broadly separating the eyes at the distal tips of the cephalofoil. In sphyrnid sharks the eyes are canted slightly forward which provides them with greater binocular overlap (30˚) than their carcharhinid sister taxa (10˚). However, the widely spaced eyes create a larger blind area immediately anterior to the snout in sphyrnids, which would seem to be a detriment for an apex predator. At close ranges (tens of cm) the electrosensory system informs the sharks about the location of prey near the head. Juvenile carcharhinid and sphyrnid sharks orient to prey-simulating electric stimuli from a mean distance of 25cm, and maximally from a distance of 40cm. This electrosensory range completely overlaps the anterior blind area of juvenile scalloped hammerhead sharks, Sphyrna lewini, and overlaps nearly the entire anterior blind area of a similar sized, representative carcharhinid species, the blacknose shark, Carcharhinus acronotus. By integrating visual and electrosensory information, both species are able to continuously track prey right up to the mouth with no loss of spatial information. Therefore, the sphyrnid head morphology confers several advantages and any potential disadvantages are mitigated by sensory integration.