The acoustic properties of a deep scattering layer located north of Bermuda were examined over the frequency range from 0.4 to 6.4 kc/sec. Octave-band scattering strengths were measured in the two octaves from 1.6 to 6.4 kc/sec. A broad peak in scattering strength was observed whose center frequency decreased over the sunset period from an average daytime value of 5.4 kc/sec to an average nighttime value of 4.8 kc/sec. The variations in measured scattering strengths, resonant frequencies of scattering-strength peaks, and layer depths were consistent with those expected from a migrating layer of scatterers possessing swim bladders of constant volume.