MAPPING THE SHAPE, SIZE, AND DENSITY OF FISH SCHOOLS BY ECHO INTEGRATION AND A HIGH-RESOLUTION SONAR

The shape and horizontal extent of herring schools in the North Sea ha ve been mapped by a naval sonar (SIMRAD SA 950) with a narrow horizont al beam. The density of schools surveyed was measured by the SIMRAD EK 500 echosounder. In most cases the school shape fitted a geometric ca tegory (circle, oval, square, rectangle, parabola), but a few schools showed an undefined, amorphous appearance. Fish density within schools varied by a factor of about 100, but there were clear relationships b etween the geometric dimensions and biomass of the schools. The variat ion in the dimension-to-biomass relationships was substantially reduce d by classifying the schools by density.