TRUMBLE ET AL.: STRAIT <)E GEORGIA HERRINC FISHERY 



Figure 1.— Strait of Georgia standard 

 track line pattern (....)• Solid lines and 

 10-fathom contour (--•) define survey 

 subareas (from Lemberg 1978). 



fathom contours on the outside. Spawning occurs 

 on adjacent shorelines. 



The surveys were conducted at night when the 

 herring were less patchily distributed and 

 further off bottom. Transects were evenly spaced 

 and designed for maximum mileage during 

 hours of darkness. At about 0.5 h per transect, 

 plus turn around and set up time between 

 transects, each survey required the approxi- 

 mately 6 h of darkness. 



Data were integrated for density (kg/m 3 ) at 

 preselected depth intervals for each transect; 

 depth interval densities were accumulated for a 

 depth zone, usually 5-40 m below the surface to 

 calculate an average density (kg/m 2 ) for each 

 transect. Extrapolation of average density to the 



surface area represented by each transect, 

 summed over all transects, provided biomass 

 estimates. The acoustic estimates of maturing 

 adult herring biomass were available the after- 

 noon following each survey. 



Midwater Trawling Procedures 



The midwater trawl sampling was done from 

 chartered 20-24 m commercial fishing trawlers 

 simultaneously with the acoustic surveys. This 

 procedure has two advantages in addition to 

 synopticity. First, the vessel requirements for 

 the acoustic vessel are less demanding so that a 

 smaller, less expensive vessel could be used. 

 Second, it was possible to direct the towing 



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