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Appendix I: Procedure used for estimating 

 the swept transect area 



At each sample unit (submersible (iive site), we estimated 

 the total swept transect area, where the swept area (m^) = 

 (average area swept per second [m-^/sec]) x (total elapsed 

 time [seconds] ). The average area swept per second ( m'^/sec) 

 was computed for a set of randomly selected thirty second 

 portions of each transect. Conceptually, we determined the 

 average area swept per second for the subsampled areas 

 from a series of adjacent trapezoids (Fig. 1). 



For each trapezoid, we determined swept area (A,) by 

 measuring the width that was swept (/, ) and distance that 

 was swept (T,), where 



A =-(/,+/,.: )?;• 



2 



The process involved a frame-by-frame analysis of the 

 video image, which required tracking an object from the 

 center of the video monitor display to the bottom edge of the 

 video display for a known time interval ( Fig. 2 ). The elapsed 

 time for this interval was obtained from the video frame 

 count, and was used to calculate area swept per second. 



Width-swept estimates (/,) were calculated from 1 ) the 

 distance between the laser spots on the video monitor 

 display (w,), 2) the width of the video monitor display (V), 

 and 3) the known distance between the lasers (W) (20 cm), 

 where 



Submersible path 



Area 3 



Area 2 



Area 



Figure 1 



Schematic representation of adjacent trapezoids. 



/; = 



VW 



(1) 



Because the width that was swept varied as the submers- 

 ible distance olT bottom varied, it was measured for each 

 block. The following procedure was performed in sequence: 



