FISHERY BULLETIN: voL 76, NO. 1 



METHODS 



Food 



For interspecific comparisons, collections were 

 made over a single isolated reef, where the three 

 species probably exploit a common forage base. 

 Naples Reef is a large rocky outcrop surrounded on 

 all sides by sand flats and forested by lush stands 

 of giant kelp, Macrocystis. It is located about 1.6 

 km offshore, 24 km west of Santa Barbara (lat. 

 34°25'N. long. 119°57'W). Covering an area of 

 about 2.2 ha, the reef averages 8-10 m in depth, 

 although its rocky crest projects to within 5 m of 

 the surface. It is separated from similar habitats 

 by sand and cobble flats at 16-20 m (Ebeling and 

 Bray 1976). 



We tried to collect fish as randomly as possible. 

 One of us (Ebeling) using a pole spear shot fish as 

 they were encountered, with two exceptions: he 

 ignored small juveniles and often missed large 

 kelp bass ( >300 mm SL, standard length), which 

 were consequently underrepresented in the collec- 

 tions. Thus the samples probably reflect the usual 

 size distribution of fish between ca. 100 and 300 

 mm SL over the reef (Table 1). In this way, 324 

 specimens were collected between 0900 and 1500 h 

 during all seasons from March 1971 to June 1972. 

 Of these, 80% had food in their stomachs. 



We made considerable effort not to bias stom- 

 ach-content composition. Underwater chumming 

 or disturbing the bottom were never used as ways 

 to attract fish near the collector. Spearing was 

 begun only after it was ascertained that no sport 

 fishing involving chumming with live bait (usu- 

 ally northern anchovy, Engraulis mordax) occur- 

 red within visual range of the collecting site. An 

 initial practice of securing individual fish in plas- 

 tic bags or locking their mouths with paper clips 

 was soon discontinued when no individual was 

 seen to regurgitate food. All specimens were 

 placed immediately in an ice chest aboard the div- 



ing skiff. In the laboratory, they were measured 

 (nearest millimeter SL), slit open, and their intes- 

 tines detached and measured (millimeters SL). 

 Other trophic structures (jaw length, gill rakers 

 on first arch, and greatest width between gill rak- 

 ers) were measured on a few typical specimens of 

 about 225 mm SL. Specimens were then fixed in 

 10% Formalin^ and preserved in 50% isopropanol. 



To investigate the effect of habitat on the olive 

 rockfish's diet, one of us (Love) collected an addi- 

 tional 110 individuals from One-Mile Reef, an 

 open, rocky reef located 1.6 km offshore of Santa 

 Barbara Harbor, about 20 km east of Naples Reef 

 Of these, 72 (65.5% ) had stomachs containing food 

 (Table 1). Too deep and turbid to support kelp, this 

 reef is made up of a strip of rocky bottom at about 

 27 m depth, with 1.5-5.0 m high rock piles scat- 

 tered along its length. From January to October, 

 fish were caught by angling with artificial lures 

 and by gill net. No sport fishing or chumming were 

 seen to occur during collecting. Fish were pre- 

 served and processed as before. 



Gut fullness was estimated before stomach con- 

 tents were sorted and identified. Degrees of full- 

 ness of stomach and of the first half of the intestine 

 were scored from 1.0 (empty) to 5.0 (full). Stomach 

 contents were sorted taxonomically into 26 food 

 items (Table 2). The volume of each item was mea- 

 sured by liquid displacement. The "nekton" cate- 

 gory of items (prey type) included all nonlarval 

 fish and squid prey. The substrate-oriented prey 

 type included all prey (except fish) that live on or 

 about reef and plant surfaces. Such prey are either 

 motile like shrimps, amphipods, and small crabs, 

 or attached like hydroids, bryozoans, and the 

 algae itself. Plant material was identified as 

 either kelp (Macrocystis) or other algae, mostly 

 low lying browns and reds. In computing percent 

 volumes and frequencies of occurrence of prey per 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Table l. — Number, size, and food containment of specimens examined of the three species of kelp-bed fishes (blue rock- 

 fish, kelp bass, and olive rockfishi from Naples Reef or One-Mile Reef (olive rockfish only) off Santa Barbara, Calif See also 

 Figure 1. 



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