| Afler a short review of acoustic principles, methodology and purposes of accustic surveys are described and some examples given. IFREMER instrumentation, strategy and calculations used during echo sur veys are described in details and criticized. Five acouslic sur veys carried o t in the Bay of Biscay between 1983 and 1987 show that several species are generally mixed , and lheir identification is very oflen biased by behaviour phenomena. A new way of classi fying echotraces and interpretating data has been applied to these surveys. The results are summarized in tables and maps. Whenever multispecies structures are concerned, it seems at present impossible to assess absolute biomasses based on acoustic survey method. ln such a situation, acoustic surveys... |
