For the purpose of this exercise, i.e., comparing the results of the acoustic method of population estimation with an estimate obtained by recapturing previously marked vendace, the capture-mark-recapture experiment was a failure. This was due to two factors. Firstly the preliminary echo-survey showed conclusively that the vendace were not distributed uniformly or randomly over the whole lake. There were few in the shallower parts and very large shoals in the deeper water, and there was no way independent of the echo-survey of accurately assessing even the relative numbers at different depths. Secondly no marked vendace were found in the trawl catches. The total number of vendace caught in the series I to III trawl catches was 419 and commercial seine catches suggested that the number of marked fish was 1 in about 700. It is clear that the capture-mark-recapture method could not be used for estimating the number of vendace in the area surveyed by the echo-sounder.
