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Sharks have become practically legendary for their sensory abilities. Some of the recognition is deserved, and some is often exaggerated. Accounts of sharks being able to smell or hear a single fish from miles away may be fish stories, but controlled measurements of elasmobranch sensory function have revealed that these animals possess an exquisite array of sensory systems for detecting prey and conspecifics, avoiding predators and obstacles, and orienting in the sea. This sensory array provides information to a central nervous system (CNS) that includes a relatively large brain, particularly in the rays and galeomorph sharks, whose brain-to-body weight ratios are comparable to those of birds and mammals (Northcutt, 1978).

Sensory system performance can be quantified in many ways. In the end, elasmobranch biologists wish to know,“How ‘good’is elasmobranch hearing… smell… vision?” in a given behavioral or ecological context. To answer this basic question, sensory performance can be scaled in two general ways: sensitivity, which involves the minimum stimulus detectable by the system; and acuity, which is the ability of the system to discriminate stimulus characteristics, such as its location (direction of a sound or odor, resolution of a visual image, etc.) and type (frequency of sound, odor chemical, color of light, etc.). These parameters apply to all senses in one way or another and help to make comparisons across phylogenetic lines.