Biological and Acoustical Structure of Sound Scattering Layers Off Oregon

摘要

Four discrete acoustical frequencies were used to determine the depths of migratory and non-migratory scattering layers. Layers were insonified with a broad-band, low frequency (1-30 kHz) acoustic source and sampled with a100 m2 rope trawl with five opening and closing codends. The predominant fishes with gas-filled swimbladders caught in deep day time layers were Protomyctophum crockeri and P. thompsoni, whereas Protomyctophum spp. and Diaphus theta were the most common species in deep night-time layers. The common fishes with gas-filled swimbladders in shallow night-time layers were D. theta, Stenobrachius leucopsarus, Tarletonbeania crenularis, Symbolophorus californiensis and Engraulis mordax. Arcer estimates of distributions of bubble radii were similiar for deep day and deep night scattering layers, but a wider range of bubble sizes existed in shallow night-time layers than in deep day and deep night layers. A model which considered species-specific parameters of morphology, physiology and behavior provided estimations of the distributions of swimbladder radii that most closely matched the acoustically estimated distributions of bubble radii. Comparisons of acoustic data and net catch data indicate that myctophids with gas-filled swimbladders may maintain swimbladder volume at a level below tht required for neutral buoyancy; smaller myctophids may maintain a constant swimbladder mass during vertical migration.