Comparison of the acoustic and biological sampling of the sonic scattering layers: R.R.S. ‘Discovery’ SOND Cruise, 1965

Abstract

The acoustic measurements made during the SOND cruise are presented in the form of vertical profiles of relative scattering coefficient at day and night and its time dependence over sunrise and sunset for the four echo-sounders used. These profiles are compared with the scattering which is calculated would be returned from the vertical distributions of biological samples reported by other workers, but particularly from the distribution ofswimbladder fish analysed by Badcock. The similarities between the calculated and measured profiles support the assumption that swimbladder fish dominate the scattering due to their high target strengths, particularly at frequencies up to and including 36 kHz. By correlating fish sizes, daytime depth, migration behaviour and acoustic scattering several of the layers may be tentatively attributed to particular species. A calibrated echo-sounder in the frequency range up to 36 kHz is size selective, but can nevertheless be useful for looking at broad distributional features. However, because the numerically more abundant small planktonic animals are inadequately represented by the sounder the records are little more than a guide to net sampling programmes.

Diurnal signals in vertical motions on the Hebridean Shelf

“…This consistency, together with the precise phase locking of the migration to solar time, has led us to conclude that, up until day 201, a significant proportion of the scatterers were performing diel migration. The observed migration rate was about 0.02 m s-l, which is in agreement with estimates made from echo sounder measurements (McCartney 1976), other ADCP measurements (Plueddemann and Pinkel 1989;Roe and Griffiths 1993), and with speeds inferred from the results of zooplankton trawls (Enright 1977;Hays 1996). It should be noted, however, that the vertical velocity estimated for a particular depth bin, by the ADCP is the mean value for most of the scatterer population in that bin, including nonmigrating scatterers but excluding any individuals with migrations so large (>5-6 cm s-l) they did not lie within the spectral window for the analysis.…”

First record of a tropical shallow water barnacle Tetraclita sp. (Cirripedia: Tetraclitoidea) from the middle Neogene of the Canary islands

“…Estas especies migran desde unos 300-600 m hasta la zona superficial (epipelágica) de manera parecida a como lo hacen en otras áreas marinas tropicales y subtropicales (Vinogradov, 1962;Longhurst, 1976). Estudios de Clarke (1973), Roger (1974), McCartney (1976), Tarling et al (1999), sobre acústica y pesca con redes, indican que estos organismos de las DSL no alcanzan las capas más superficiales como consecuencia de la iluminación lunar (Blaxter, 1974). Como sigue indicando Yebra (op.cit.)…”