DIGITAL HYDROACOUSTIC DATA- PROCESSING SYSTEM AND 

 ITS APPLICATION TO PACIFIC HAKE STOCK ASSESSMENT 

 IN PORT SUSAN, WASHINGTON! 



Richard E. Thorne- 



ABSTRACT 



A digital hydroacoustic data-processing system was developed at the University of Washing- 

 ton utilizing the general-purpose computer PDP/81.. The system, which functions as a 20- 

 channel squared voltage integrator, was applied to the annual assessment of the spawning 

 stock of Pacific hake, Mcrluccius productus, in Port Susan, Wash. Four surveys were con- 

 ducted between 14 and 16 March 1971. The population estimates based on calibration by 

 net hauls ranged from 15.9 to 18.8 million lb. An estimate of 18.2 million lb was obtained 

 with an analog voltage integrator for one of the surveys. The digital system provided more 

 detailed information on the horizontal and vertical distribution of the fish and resulted in a 

 much smaller variance of the estimated mean fish density than the analog system. 



Echo sounders have been used extensively 

 since 1950 as a means of studying the distri- 

 bution and relative abundance of fish popu- 

 lations, but only during the last decade has the 

 tedious interpretation of echograms begun to 

 be obviated by the development of electronic 

 devices for automated signal processing. These 

 are basically of two types, echo counters 

 (Mitson and Wood, 1961; Carpenter, 1967; 

 Dowd, 1969) and echo integrators (Dragesund 

 and Olsen, 1965). The principles governing the 

 application of acoustics to fish abundance esti- 

 mation are described in Parrish (1969). 



An analog echo integrator was designed and 

 built at the University of Washington (Lahore, 

 1969) as part of a general study of acoustic 

 methods of resource assessment in the Univer- 

 sity's Sea Grant Marine Acoustics Program. 

 It was used in investigations of the relationship 

 between integrated echo voltage and fish den- 

 sity (Thorne, 1971) and of the population size 

 of juvenile sockeye salmon, Oiicorhynchiis 

 lu'vka, in Lake Washington in 1969 (Thorne 

 and Woodey, 1970) and of Pacific hake, Moiuc- 

 ci/i.s productus, in Port Susan in 1969 and 



' Contribution No. 382, College of Fisheries, Univer- 

 sit;^ of Washington, Seattle, Wash. 



- Fisheries Research Institute, College of Fisheries, 

 University of Washington, Seattle, WA 98195. 



1970 (Thorne, Reeves, and Millikan. 1971). It 

 became apparent during these investigations 

 that integration with analog echo integrators 

 had several disadvantages, such as instability 

 and limited dynamic range, which could be 

 eliminated by suitable digital circuitry. Con- 

 sequently, a digital processing system was de- 

 signed and built around a small general-purpose 

 computer. A preliminary report of the Digital 

 Data-Acquisition and -Processing System 

 (DDAPS) was reported in Moose, Thorne, and 

 Nelson (1971). A detailed description of the 

 system and its initial application to the popula- 

 tion assessment of Pacific hake in Port Susan, 

 Puget Sound, Wash., in 1971, is presented here. 



MATERIALS AND METHODS 



The Digital Data-Acquisition and 

 -Processing System 



The DDAPS is constructed for use with the 

 general-purpose computer PDP/8L. 4 K mem- 

 ory, manufactured by Digital Equipment Com- 

 l)any. A block diagram is shown in Figure 1. 

 The amplified signals from either one or two 

 echo sounder transducers are envelope detected, 

 low pass filtered, multiplexed (should two 

 sounders be in use). A/D converted into 8-bit 

 binary words, and then digitally squared in a 



Manuscript accepted February 1973. 

 FISHERY BULLETIN: VOL. 71, NO. 3, 1973. 



837 



