Detection and discrimination of fish prey by echolocating odontocetes

Abstract

The echolocation detection range of the Atlantic bottlenose dolphin Tursiops truncates and the harbor porpoise Phocoena phocoena have been either measured or estimated in nonmasking and noise‐masking environments using human‐made targets. These experiments provide little information on the detection range for fish prey in a natural environment. Backscatter and corresponding target strength measurements were performed on four species of fish, Atlantic cod, gray mullet, pollock, and sea bass, using simulated dolphin and harbor porpoise echolocation signals. Backscatter measurements were also performed on several species of snappers using simulated bottlenose dolphin echolocation signals. The fish subject was anesthetized and placed in a monofilament net bag which was attached to a monofilament curtain attached to a rotor. The target strength and backscatter characteristics were determined as a function of angle in the lateral plane. The results of detection experiments using real targets were used to estimate echolocation detection range for the different fish species. In a nonmasking environment, a bottlenose dolphin should be able to detect a cod between 84 and 135 m and a porpoise detection range should be between 12 and 23 m. We also examined the cues echolocating animals could use to discriminate fish species.