FISHERY BULLETIN: VOL. 84, NO. 2 



displayed simultaneously on a 10-in diameter cathode 

 ray tube (CRT) screen which provided information 

 on the location and size of fish schools within its 

 200-400 m wide path (Fig. 10). 



Data was collected electronically during the echo 

 integration and sonar surveys. Echo sounder return 

 signals were processed by an echo integrator capable 

 of measuring voltages in variable-sized depth inter- 

 vals. The echo integrator produced periodic printouts 

 of summed integrated voltage values which corre- 

 sponded to relative fish densities along the transect 

 in various depth intervals. Analog data (receiver out- 

 put voltages) were recorded onto magnetic tape as 

 a back-up procedure and for further processing. The 

 sonar CRT display screen was video-taped for play- 

 back and data reduction in the NWAFC laboratory. 



Survey design of the 1980 and 1981 FRI studies 

 off southern Washington was generally similar, 

 though some aspects differed. In 1980, preselected 

 tracklines were run and were between lat. 46°20'N 

 and 46°48'N and between 55 and 183 m isobaths at 

 intervals of of 3.7 km. When a significant aggrega- 



tion of fish was encountered, its bounds were deter- 

 mined by making several mapping runs perpen- 

 dicular to the main trackline. Trawling followed to 

 determine the species composition of the aggrega- 

 tion and to collect biological samples. Most of the 

 1980 work was done during daylight with the intent 

 of mapping and measuring yellowtail rockfish, 

 Sebastes flavidus, schools. After encountering 

 numerous widow rockfish schools at night, it became 

 apparent that this species' schooling behavior was 

 better suited for evaluating this methodology. 

 Thereafter, three nights were spent transecting a 

 smaller "widow rockfish subarea". Diel behavior and 

 distribution were examined by making several repeti- 

 tions of three selected tracklines. Near the end of 

 this cruise an area occupied by a dense aggregation 

 of widow rockfish schools was encountered. A short 

 nonrandom transect was run to obtain comparable 

 line intercept and line transect results. 



In 1981, tracklines spaced every 3.7 km were 

 transected between the depths of 128 and 220 m off 

 northern Oregon between lat. 45°50'N and 46°18'N. 



Figure 10.— Measurements and calculated dimensions of fish schools from videotaped sonar records. 



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