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Hydroacoustics 



One recent and potentially valuable development in assessment work 

 concerns hydroacoustics. Fishermen have now used such electronic aids 

 as sonars and "fishfinders" for over a decade. While it remains impossible 

 to determine the species of fish seen on the recording paper of such 

 electronic aids, it j_s possible to see fish. Fishermen claim that they 

 can, with a good fishfinder, spot individual fish at great depths. The 

 basis of such a belief is experience: they see such targets, shoot their 

 net, and retrieve some fish. Over time, they learn to read the recorder; 

 this, just as aging fish, is considered to be an "art." 



Hydroacoustics, properly developed, could be tremendously valuable 

 for assessment work. Instead of requiring survey tows at selected areas, 

 it might become possible to take a steady record of fish abundance as 

 the vessel proceeds along a chosen course. Were it possible 

 to determine the species of the target, abundance surveys could be under- 

 taken far more rapidly and at far less cost than existing survey tows. 



Presently, however, there is uncertainty as to the potential of 

 hydroacoustics. Present technology limits hydroacoustics to schooling 

 stocks, clear awareness of possible bias, and location in midwater depths. 

 Such techniques can be used productively in known areas but not in 

 frontier areas; it remains impossible to distinguish one species from 



