Fish counting by acoustic means

During the past ten years Bendix, in conjunction with the Alaska Department of Fish and Game, has been developing acoustic fish counters. Early development included doppler systems which evolved into the present day, bottom-mounted, upward-facing counters for enumeration of migrating river fish which range in size from 50 mm to 1,000 mm. The present systems which are undergoing continuing development, have demonstrated accuracies as high as 95 percent compared to visual counts on migrating sockeye salmon (Onchorhynchus nerka). In 1970, a biomass counter was developed to enumerate downstream migrating schools of fingerling salmon smolt that average 100 mm in length and 50 fish to the pound. Three such systems are currently in use in Alaska and calibrations performed by Alaska´s netting have shown long term accuracies better than 96 percent. A recent development is an acoustic smolt counter used in conjunction with a fyke net tunnel. Initial results show great promise for this system. Development of a biomass herring counter for the east coast of the United States is eminent. This system will count upstream migrating herring and automatically convert the biomass input to actual numbers of fish which will be displayed on a digital readout.