抄録
Recent progress of underwater techniques for fisheries resources surveys is reviewed. The most important technique for the purpose is quantitative echo sounders. The technique is classified into three categories : estimation for individual fish which includes the echo counting method and in situ target strength measurement; estimation for individual school which includes density measurements in school; and echo integration method which is the most popular tool for abundance estimations. These methods are explained briefly. Some types of quantitative echo sounders are introduced and some advices for installing them are given. To perform a successful survey, some watching work is necessary, such as observing noise contamination and setting a threshold level to cut the noise. Future developments in this field are discussed and some powerful techniques such as the echo trace analysis for fish behaviour observation and the multi-frequency observation for plankton size and abundance estimation.
