WILKINS: ABUNDANCE OF WIDOW ROCKFISH 



the University of Washington's Fishery Research In- 

 stitute (FRI) under contract with the NWAFC 

 (Gunderson et al. fn. 7, 8). The objectives of the work 

 were to evaluate the applicability of several resource 

 assessment techniques and refine the most prom- 

 ising approaches. In particular, it involved a compar- 

 ison of three methods of quantifying widow rockfish 

 abundance in small areas off southern Washington 

 and northern Oregon: conventional echo integration, 

 line transect survey theory (Burnham et al. 1980; 

 Seber 1980), and line intercept survey theory (Seber 

 1973, 1980). 



Methods 



This study involved three research cruises off 

 southern Washington and northern Oregon. Tables 

 2-4 present the dates of these cruises and specifica- 



8 Gunderson, D. R., G. L. Thomas, P. Cullenberg, D. M. Eggers, 

 and R. E. Thorna 1980. Rockfish investigations off the coast of 

 Washington. Annual report. Unpubl. manuscr., 68 p. Univ. Wash., 

 Fish. Res. Inst., FRI-UW-8021. 



tions of the vessels, fishing gear, and hydroacoustic 

 equipment employed. The field work entailed system- 

 atically transecting the survey areas, simultaneously 

 recording data from quantitative echo integration 

 equipment and sector scanning sonar. Data were col- 

 lected on the number of fish schools, their perpen- 

 dicular distance from the transect, their depth below 

 sea surface, the size and density of selected schools, 

 and the distribution of schools in relation to various 

 features of submarine topography. The echo integra- 

 tion system was used in a conventional manner to 

 obtain a measure of the density of fish within a 

 relatively narrow acoustic beam of 10°-11° directly 

 below the vessel (Fig. 9). Sector scanning sonar can- 

 not measure fish density, but by employing an ar- 

 ray of transducers radiating an acoustic signal over 

 a 200° x 9° semicircular wedge perpendicular to the 

 path of the vessel (Fig. 9), it can be used to count 

 schools within about 100-200 m to each side of the 

 vessel, measure their dimensions, and determine 

 their perpendicular distance from the transect. The 

 sonar's transducer array was aimed straight down- 

 ward for these studies. The entire wedge was 



ECHOSOUNDER 



SONAR 







s 



Figure 9— Schematic diagram depicting the analysis of echo sounder and sonar data collected during hydroacoustic line transect surveys. 



297 



