FISHERY BULLETIN: VOL. 76, NO. 1 



hydroids (especially Sertularia), caprellid am- 

 phipods, and kelp ranking highest among such 

 items. Most caprellid amphipods were found in 

 stomachs containing substantial amounts of hy- 

 droids and bottom algae, indicating that fish may 

 ingest such turf for the contained animals. About a 

 third of all pieces of kelp bore attached bryozoans 

 (Membranipora) or hydroids. 



Whether speared from Naples Reef or angled 

 from One-Mile Reef, olive rockfish ate relatively 

 more fish than did the others (Table 2, Figure 1). 

 Recognizable fish prey in Naples Reef individuals 

 included juveniles of blacksmith, Chromis 

 punctipinnis, anchovy, pipefish, blue rockfish, 

 other olive rockfish, and adults of topsmelt and 

 anchovy. One-Mile Reef fish had eaten adult an- 

 chovies and a young pipefish. Fish larvae made up 

 a relatively large part of the diets of olive rockfish 

 from both localities. One-Mile Reef fish ate more 

 kinds and greater numbers of small zooplankton. 

 Individuals of all sizes ingested and retained such 

 tiny prey as ostracods, cladocerans, and small 

 copepods (e.g., Coryceus emarginata). During the 

 winter, copepods and zoea larvae actually out- 

 ranked fish prey in volumes consumed. Many 

 polychaetes, which occurred commonly in fish 

 from either area, were of the small nereid variety 

 found in the kelp canopy (Quast 1968c) and 

 swarming in the midwater plankton at night 

 (Hobson and Chess 1976). Only olive rockfish con- 

 tained parasitic copepods among their stomach 

 contents. Although these copepods were identified 

 as Caligus, an obligatory ectoparasite, olive 

 rockfish were not observed to clean (i.e., pick such 

 prey from off other host fishes). 



Individual Variation 



On any given day, individuals of the same 

 species tended to select the same food item. Within 

 particular collections of 2-9 individuals, 67% of a 

 cumulative total of 96 blue rockfish, 60% of 72 kelp 

 bass, and 60.5% of 86 olive rockfish had the same 

 item dominating their stomach contents. 



Occasionally, individuals of all three species 

 selected items from the same major prey category, 

 although not necessarily the same item (Table 3). 

 Plankton dominated the stomach contents of most 

 individuals sampled together in a February and in 

 an April collection, while nekton and substrate- 

 oriented prey were favored by those in three May 

 and in one October collections. Yet fish in two 

 November and two January collections showed 



262 



little communality of diet. And even when they 

 tended to select items from the same prey type, as 

 in the February, April, May, and October collec- 

 tions, they often selected different items. For 

 example, most blue rockfish collected on 22 Feb- 

 ruary 1972 had mostly salps or chaetognaths in 

 their stomachs; kelp bass contained either salps or 

 copepods; and olive rockfish contained larval fish. 

 On the other hand, all blue rockfish and most kelp 

 bass in the 21 January 1972 collection had eaten a 

 single planktonic item, namely salps. 



Fish usually selected the same prey type during 

 a particular feeding bout (Table 4). For all species 

 pooled, 76% of the individuals contained more 

 than 95% by volume of items in a single major prey 

 category (prey type), and 39% contained but a 

 single item (20% with relatively small items, 19% 

 with large items). Combinations of prey types var- 

 ied among the three species: usually plankton and 

 substrate-oriented prey for kelp bass, and 

 plankton and nekton for olive rockfish (Table 4). 

 Of all fish containing kelp, etc. (Figure 1), about 

 40% also contained relatively large amounts of 

 substrate-oriented prey, about 15% each also con- 

 tained relatively large amounts of plankton or 

 nekton, and the remainder contained kelp only. 

 About 83% of 81 specimens with recognizable prey 

 in both stomach and intestine had the same prey 

 type dominating the contents of both. 



Seasonal Variation 



Considering all 26 food items, diets were 

 weakly, though usually significantly concordant 

 among seasons (Table 5). Fish ate relatively 

 greater volumes of plankton during winter-spring 

 periods, and more nekton or substrate-oriented 

 prey during summer-fall. Showing the greatest 

 seasonal variation (least concordance), the blue 

 rockfish's diet included 93% plankton (by volume) 

 in the winter, 75% in the spring, and less than 8% 

 in summer-fall. Tunicates ranked high from De- 

 cember to August, while kelp (with encrusting 

 animals), hydroids, and, later, fish, ranked high 

 from March to November. Similarly, olive rockfish 

 from One-Mile Reef contained 80%, 25%, and 

 < 10% plankton (by volume) in the first three sea- 

 sonal periods, respectively. Small crustaceans 

 ranked high from December to August, while fish 

 and polychaetes ranked high from March to 

 November. Individuals of both species ate larval 

 fish during late winter and spring when such prey 

 are most abundant. Seasonal trends for the others 



