Measurements of volume backscattering strength have recently been made to a depth of 1500 m in the Northeast Atlantic. Scattering layers with strengths of −80 dB and −70 dB have been found at depths of approximately 500 and 1000 m, respectively. The layer at 1000 m has been shown to comprise fish shoals distributed with a density of 3.2 in 108m3, each shoal having a target strength of about −6 dB and comprising about 50 fish. Each fish is thought to have a swimbladder resonant at 2 kHz at 1000 m and hence to have a radius of 1.6 cm. The shoals have been shown to vary with geographical location but not with the time of day, 1000 m being about the maximum depth of daylight penetration. The layer at 500 m does not vary much with geographical location but does exhibit diurnal variations due to the well‐known vertical migration of fish in a diurnal cycle.Subject Classification: [43]30.40.