FISHERY BULLETIN: VOL. 76, NO. 1 



SIZE GROUP (STANDARD LENGTH) 



80-150 151-200 201-300 30l-400mm 



(-) 



BLUE 

 RKF. 



(-) 



KELP 

 BASS 



OLIVE 



RKF. 



(NAPLES) 



OLIVE 



RKF. 



(1-MILE) 



P 

 N 

 S 

 K 



(-) 



p 



N 

 S 



83% 



17% 

 17% 



222 



P<0.005 



05>P>0.025 



M P^oos 



Figure l. — Percentage frequency of prey types (bars and num- 

 bers) in stomachs offish in all size groups of the three species of 

 kelp-bed fishes from Naples Reef (all three species) or One-Mile 

 Reef (olive rockfish only) off Santa Barbara, Calif Prey types are 

 designated: P, plankton; N, nekton; S, substrate-oriented prey; 

 and K, kelp and other algae (with encrusting bryozoans), and are 

 represented by any constituent food item under the appropriate 

 prey-type heading in Table 2. Numbers in parenthesis are num- 

 bers of fish stomachs examined. Hatching shows significantly 

 different frequencies at the indicated probabilities determined 

 by chi-square tests (see text). 



and 4) September-November, a period of warm, 

 clear surface water with little vertical mixing. The 

 26 food items were ranked for each season by vol- 

 ume, using data from all size groups of fishes to 

 maximize sample size (Table 5). Seasonal varia- 

 tion in diet was also tested by frequencies of oc- 

 currence of subsets of items comprising major food 

 categories, using data from the 151- to 300-mm SL 

 size group only (Figure 2). 



Habitat 



Spatial distributions of the three species were 

 determined from underwater movies taken for 

 another project. Observations were made from 

 2.5-min Super-8-mm underwater movie strips in 

 color (cinetransects) filmed by scuba divers 

 swimming courses started at random either under 

 the kelp canopy or just over the bottom at study 

 sites near Santa Barbara and across the Santa 



Barbara Channel along Santa Cruz Island (Bray 

 and Ebeling 1975; Ebeling, R. Larson, and W. 

 Alevizon in prep.). An initial set of cinetransects 

 was filmed in 1970 over a variety of habitats and 

 areas at both localities. Then, during the fall sea- 

 sons of 1971-74, transects were filmed over per- 

 manent study sites at Naples Reef and at Santa 

 Cruz Island west of Prisoner's Harbor. Fish were 

 counted by species as the films were projected in 

 the laboratory. Environmental characteristics 

 were measured or scored either on station or dur- 

 ing projection. 



Breadth and Overlap 



Breadth and overlap of resource use were com- 

 puted from values of p, , the proportion of item i 

 used by each species, either at Naples Reef (food 

 and space) or off Santa Cruz Island (space only). 

 For food, p^ is the proportionate volume of any of 

 the 26 different food items included in the species 

 total (S); for space it is the proportionate abun- 

 dance of the species in any of the 297 cinetransects 

 taken over Naples Reef or 331 cinetransects taken 

 along Santa Cruz Island. Resource breadth, B = 



s 

 l/Xp^, can be thought of as the theoretical number 



i= 1 



of equally used food items (or spaces covered by 

 cinetransects) yielding a value of B equal to the 

 observed. For example, if all items are in equal 

 proportions, B equals S, the total items in the 

 spectrum (see Bray and Ebeling 1975). A Hill's 

 (1973) ratio was used to estimate the degree of 

 concentration of each species among cinetransects 

 (the unevenness of distribution offish numbers): 

 HR = exp(H')/5, where H' is the Shannon- 



s 

 Weaver measure of diversity , -2p, Inp,. Since i/' 



1=1 



is more sensitive to changes in the small to 

 medium values of proportionate abundances than 

 is B, their ratio is a sample-size independent mea- 

 sure of concentration of observations (Peet 1974). 

 Overlap between two species, / = 1.0 - [0.5 



s 



(X\pij - P'L I)], where p J is the proportion of item i 



1=1 



used by species 7 and s is the species total of food 

 items eaten (or cinetransects in which recorded), is 

 scaled from zero (complete discordance of item use) 

 to 1.0 (all items used in equal proportions) (e.g., 

 Whittaker 1960; Cody 1974; Ebeling and Bray 

 1976). 



260 



