LARSON and DeMARTINI: DISTRIBUTION OF FISHES IN KELP FOREST 



TABLE 2.— Bathymetric sampling strata at the San Onofre kelp bed. 

 Weighting factors (WJ are shown for the above-bottom strata and 

 for the above-bottom versus bottom strata. 



'Weighting factor for above-bottom strata combined. 



which time fish that were distinguishable on film 

 were identified, counted, and assigned to maturity 

 classes as above. 



Transect Volume 



The volume of visual bottom transects was con- 

 sidered to be fixed, and the volume of water-column 

 cinetransects to be dependent on underwater 

 visibility. The volume of bottom transects was fixed 

 at75mX 3mX 1.5 m = 337.5 m\ since the length of 

 transects was measured, and the height and width of 

 transects were fixed at values less than horizontal 

 visibility. Cinetransect length was taken as the 

 average distance covered in simulated, 3-min cine- 

 transects swum by three divers over a metered line. 

 Each diver swam two simulations against the current, 

 and two with the current. The cross-sectional area of 

 a cinetransect was treated as an ellipse with a minor 

 (vertical) axis of 1.5 m, the distance above and below 

 the diver that fish were photographed. The major 

 axis of the ellipse was a function of camera range, the 

 distance at which fish could be distinguished on film. 

 The particular function was cos 30° X camera range, 



since divers photographed fish within a 120° arc (60° 

 on each side of the transect axis) (Fig. 2). Thus, the 

 volume of cinetransects at a given depth on a given 

 day was calculated as 



V= 1.5 ttL (cos 30° X CR), 



where V was cinetransect volume in cubic meters; 

 1.5, the minor axis of the ellipse; L, the cinetransect 

 length as determined above; and CR, the camera 

 range at that depth on that day. Camera range itself 

 was estimated as a function of the horizontal 

 visibility at a depth on a sampling date. 



The relationship between camera range and 

 horizontal visibility was estimated empirically under 

 different conditions. The main "other condition" 

 that we evaluated was the orientation of the camera 

 to the sun. In trials run at different visibilities, two 

 fish of similar appearance (usually a kelp perch, 

 Brachyistius frenatus, and a white seaperch, 

 Phanerodon furcatus) were held on a spear by one 

 diver and photographed with our usual equipment by 

 another diver at distances decremented from the 

 limits of horizontal visibility (measured as described 

 above). At each visibility, trials were run with the 

 camera facing into the sun and with the camera facing 

 away from the sun. Two observers viewed the film 

 from each trial and determined camera range as the 

 greatest distance at which the two fish could be dis- 

 tinguished on film. The criteria for distinguishability 

 were the same as those used in evaluating whether or 

 not to count a fish when we viewed regular 

 cinetransects. 



Data for camera range versus horizontal visibility 

 were fit to several asymptotic functions. The fitting 



CINETRANSECT VOLUME 



A. CINETRANSECT 

 SHAPE 



B. CINETRANSECT 

 CROSS SECTION 



Camera Range 



FIGURE 2.— A. Estimated shape of area sampled in under- 

 water transects taken with motion pictures (cinetransects). 

 The length of 76 m was estimated from simulated tran- 

 sects. B. Elliptical cross section of a cinetransect, with 

 minor axis (a) of 1.5 m and major axis (b) calculated from 

 camera range when divers surveyed a 120° horizontal arc 

 about the central axis of the transect. 



