HYDROACOUSTIC MEASUREMENT OF THE DENSITY OF THE BAIKAL MACROZOOPLANKTER MACROHECTOPUS-BRANICKII

Experimental studies and statistical analyses were performed to evalua te hydroacoustic methods for assessing the density of Macrohectopus br anickii (Amphipoda, Gammaridae) in Lake Baikal. Minimal registered abu ndance (expressed as volume) appeared to be < 1 Mg m-3 (echosounder at a frequency of 200 kHz). Patterns of Macrohectopus diel vertical migr ation varied with individual age, size, and sex. It is preferable to a ssess abundance of Macrohectopus at night when the population is distr ibuted primarily in the upper 100 m. Under these conditions, acoustic estimates of animal densities can be made by applying calculated data on the scattering ability of Macrohectopus within the size range of 1- 30 mm: TS(kg) = -36.8 +/- 0.5 dB kg-1 (mean +/- 95% C.I.).