Results of experiments on the video-acoustic estimation of fish target strength in situ

Abstract

Abstract Present methods for determining the target strength (TS) of fish do not meet the requirements of accuracy, since they are not provided with reliable working standards and therefore have no correct metrological basis. Attempts to develop such a basis by means of catch analysis have not brought good results, because any fishing gear is selective, and TS measurements of single fish in situ are uncertain when data on their length distribution and behaviour are lacking. To overcome this difficulty, the Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO) has been developing a video-acoustic method to measure TS of fish in situ. The method involves the processing of two independent data flows from the same fish received synchronously through the acoustic and video channels. Good matching of the effective ranges of both channels can be achieved by maximizing the underwater visibility range of the video camera. To this end, the laser underwater television system (LTV) was used. Field experiments showed the visibility range of the LTV to be 3.2 times that of the ordinary underwater video.