FISHERY BULLETIN: VOL. 71, NO. 3 



were equipped with Ross 200A Fineline echo 

 sounders,'' with a frequency of 105 kHz and a 

 pulse length of 0.6 msec. The transducers pro- 

 duced circular beams approximately 8° full 

 beam angles to the -6 dB points. The echo 

 sounding data were heterodyned to 6 kHz and 

 recorded on analog magnetic tape for later 

 analysis. Details of the data-acquisition system 

 are given in Thorne, Nunnallee, and Green 

 (1972). Net hauls were made with the pelagic 

 trawl described in Thorne (1971). The net fil- 

 tered approximately 30,000 m^ in a 10-min 

 tow. 



Data Analysis and Calibration 



The echo data collected on magnetic tape 

 during both the surveys and the net hauls were 

 analyzed with the DDAPS. Integrated squared 

 voltages were determined in 10-m depth strata 

 from 60 m to 120 m. The relationship between 

 integration and fish density was computed from 

 the net catches as in previous surveys (Thorne 

 et al., 1971). Integrated squared voltages were 

 determined over the duration (10 min) of the 

 net hauls, and fish densities were found from 

 the net catches with an assumption of 100% net 

 efficiency and regressed against the integrations 

 from the corresponding 10-m depth strata in- 

 cluding the mean depths of the net. The depths 

 of the net were determined by the use of an 

 electrical telemetry system (Lusz, 1967). Then 

 this relationship was used to determine fish 

 densities from the integrations along transects. 

 During analysis of the data collected on tran- 

 sects, integrated voltages and corresponding 

 densities were usually put out every one-third 

 of each transect. 



Data from one of the surveys (14 March) and 

 the net hauls were also analyzed with an analog 

 voltage integrator for comparison. The inte- 

 grator used was the unsquared voltage inte- 

 grator described by Thorne (1971). Integrated 

 voltages were determined over 10-m intervals 

 centered on the mean depths of the net. The 

 relationship between integrated voltage and fish 

 density was computed as above. Integrated 



voltages and corresponding densities were 

 found over the complete duration of each tran- 

 sect in each of the depth intervals 60-75 m, 

 75-90 m, and 90 m to the bottom. 



RESULTS 



Relation Between Integrated Voltage 

 and Net Catch 



Net catches of Pacific hake and corresponding 

 integrated voltages from the DDAPS are shown 

 in Figure 4. The corresponding data from the 

 analog echo integrator are shown in Figure 5. 

 The integrated voltages from both systems are 

 definitely linearly related to respective fish 

 density as represented by catch. A linear re- 

 gression model was fitted to the data from each 

 integrator. The model was 



D = bl 



where D is catch in pounds of hake per 30,000 m^, 

 and / is the integrated voltage. 



0.04 O 08 O 12 



INTEGRATION (OOAPS) 



0.20 



•■' Reference to trade names does not imply endorsement 

 by the National Marine Fisheries Service, NOAA. 



Figure 4. — Relation between catch of Pacific hake and 

 integration output from DDAPS. 



840 



