Fig. 4. Dipole audiograms of the horn shark Heterodontus francisci (N=3) and the white-spotted bamboo shark Chiloscyllium plagiosum (N=5). Values are means ± s.e.m. Ambient noise levels found in a quiet, tidal-dominated shallow harbor are plotted for comparison (broken line). Broad-band background noise in the test tank was consistently below 10^-7 m s^-2.