Densité et mobilité des poissons sous la glace, sur une zone de pêche à la senne de deux lacs finlandais, par écho-intégration.

The density and movements of fish under ice were studied with single-beam mobile surveys and fixed location split-beam surveys, as well as exploratory fishing in winter-seining areas of two shallow Finnish lakes during winter 1999. Fish schooled near the bottom during the day but the schools dispersed and fish ascended at night. Single and split-beam target strength distributions corresponded fairly closely with the length distribution of seine catch samples. Estimated fish densities were greater at night than in daylight. The swimming speed of smelt (Osmerus eperlanus) was 0.18 m·s -1 in daylight and 0.36 m·s -1 at night. The corresponding figures for vendace (Coregonus albula) were 0.11-0…