6533b833fe1ef96bd129c07a

RESEARCH PRODUCT

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

subject

description

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 0.11-0.17 and 0.05-0.08 m·s -1 . Nights immediately before and after fishing were the best periods to estimate the effect of seining on fish density. The hydroacoustic fish density estimates at night corresponded closely with seine catches. We conclude that it is possible to estimate the effects of winter-seining by mobile under-ice echo-surveys and catch samples. © 2000 Ifremer/CNRS/INRA/IRD/Cemagref/Editions scientifiques et medicales Elsevier SAS echo-sounding / vendace / smelt / winter-seining / fish migrations