NSWC/WOL/TR 76-161 



1. The size of the area of visible kill is determined with 

 a range finder from a fixed platform. 



2. A surface trawl is towed through the area, collecting 



a representative sample of floating dead fish. (Ideally, personnel 

 on the tow boat communicate by radio with observers on the fixed 

 platform who record the boat ranges and bearings as a function of 

 time from an elevated position. Times of entry and departure from 

 the kill area, and other significant information, are also recorded. 

 A tape recorder is useful for this purpose.) 



3. A bottom trawl is then towed through the area, collecting 

 a representative sample of dead fish that have settled to the bottom 

 and benthic species that may be present. Times, ranges, and bearings 

 are recorded as before. 



4. The fish in both trawls are sorted, measured, and 

 weighed. 



5. The ratio of volume swept to the total volume is calculated 

 and is used to estimate the total fish kill. (This can be simplified 

 by calculating in terms of the surface and bottom areas and adding 

 the two results.) 



This procedure can be expected to be most reliable when the 

 following conditions are met: 



1. The area of kill is circular. 



2. The radius can be measured accurately. 



3. The fish population density is uniform throughout the 

 test site. 



4. There are sufficient fish to be statistically significant. 



5. There is no current. 



6. There is little wind. 



7. The dead fish float to the surface or sink to the bottom 

 before trawling begins. 



8. The collection efficiency and frontal area of the trawl 

 are known. 



9. The path of the boat can be accurately determined. 



10. The water is not too deep for effective handling of the 

 bottom trawl. 



11. The bottom is level and smooth. 



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