Some results of abundance estimation studies with echo integrators

Two examples of acoustic fish stock abundance estimation are given. The first is the estimation of the exploited Barents Sea capelin stock; the second is measurement of the size of the unexploited blue whiting stock. Surveys of both species were undertaken at the time of the year when conditions were favourable i.e. the fish were located as pelagic scattering layers and unmixed with other species. When the echo-sounder is operated with a TVG equal to 20 log R + 2 aR, the integrated echo intensity is proportional to the number of fish per unit area. To obtain absolute values, the system is calibrated on scattered recordings when single fish can be counted