Electroreception in Hammerhead Sharks
All living marine organisms generate an electric field around their body and all elasmobranchs possess a sensory system, the Ampullae of Lorenzini (AoL), which enables them to detect these weak electric fields and use them to orient to cryptic prey.
The electroreception research at HIMB focuses on detection of these prey-simulating electric fields in a semi-natural habitat. A 1m x 1m clear acrylic plate is placed on the bottom of the shark pond and one of four electric dipoles is activated with a weak electric current. The sharks orient to the electric field and bite it as if it were a natural prey item. The response behavior is videotaped from the surface and analyzed frame by frame to quantify orientation distance and angle which are then used to calculate the strength of the electric field at the point where the shark initiated its attack.
Positive feeding responses have been elicited from several shark species, but most of the research at HIMB is conducted with juvenile scalloped hammerhead sharks (Sphyrna lewini). Hammerhead sharks have a unique head morphology which as not arisen in any other fish. This unusual head shape may confer a sensory advantage by spacing AoL pores over a wider area and also making the lengths of the AoL canals longer than in a carcharhiniform shark. By comparing the response of hammerhead and carcharhinid sharks it may be possible to determine if the hammerheads are indeed more sensitive to weak electric fields.
Although current research examines only prey-simulating electric fields, the experimental protocol could be expanded to test a variety of attractive and adversive stimuli. Funding for the research described above was provided in part by the Raney Fund for Ichthyological Research.
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