LOVE and EBELING: FOOD AND HABITAT OF THREE FISHES 



better-fed individuals. Similarly, near Monterey 

 (ca. 300 km north of Santa Barbara), kelp beds 

 abound with all growth stages (Miller and Geibel 

 1973) eating mostly plankton, but including less 

 attached prey and more nekton as adults (Gotshall 

 et al. 1965). 



Kelp bass also show differences. Compared with 

 Santa Barbara fish, relatively more medium-sized 

 bass from off San Diego contained clupeiform 

 fishes (mainly anchovies, reflecting the bias due to 

 sampling from partyboats) and motile substrate- 

 oriented prey, such as crabs, shrimps, and am- 

 phipods; but fewer contained plankton, algae, 

 nonclupeiform fishes, and hydroids (Quast 1968c). 

 Other, more cursory results (Limbaugh 1955; 

 Young 1963) agree basically with Quast's. How- 

 ever, Turner et al. (1969), who examined kelp bass 

 speared from about oil platforms and other arti- 

 ficial reefs off southern California, found, as we 

 did, large numbers of pelagic tunicates in some 

 individuals. These researchers saw bass eating 

 chains of salps floating near the reefs. Bass would 

 first bite out and ingest the viscera of large salps, 

 then consume the tunics of the gutted prey; they 

 swallowed small salps whole. Quast (1968c) con- 

 cluded that larger kelp bass eat larger and more 

 motile prey, especially fish, and ingest more kelp. 

 Although we observed a similar trend, we have no 

 evidence that, as Quast suggested, large bass mis- 

 take kelp fragmented by boat propellers for fish 

 prey. 



These feeding differences in kelp bass cannot be 

 explained by distributional differences. Like San 

 Diego fish (Limbaugh 1955; Quast 1968b, c), all 

 sizes of Santa Barbara fish are frequently encoun- 

 tered from surface to bottom, and prefer areas of 

 dense kelp at the outer margins of the bed. Quast 

 (1968b) concluded, however, that kelp bass also 

 occupy reefs having little or no kelp. 



There is less information on geographic varia- 

 tion in feeding habits of olive rockfish. South of 

 Santa Barbara, olive rockfish and kelp bass repor- 

 tedly cooccur and even intermingle (Quast 1968d; 

 Turner et al. 1969), eat similar foods (Quast 

 1968d), and so may compete for the same cover and 

 food (Feder et al. 1974). Off Santa Barbara, how- 

 ever, the two may minimize interference by hav- 

 ing a relatively small overlap in spatial distribu- 

 tion. Considering the two species' superficial 

 similarities in body form and color pattern, Lim- 

 baugh (1955) suggested that olive rockfish may 

 ecologically replace kelp bass north of Santa Bar- 

 bara, where kelp bass dwindle in numbers (Quast 



1968a; Miller and Geibel 1973). 



Geographic variation in a fish's feeding habits 

 may reflect its environmental tolerances, range 

 limits, and numbers of competitors, as well as its 

 food supplies. Blue rockfish are more abundant off 

 central California, kelp bass are more abundant 

 off southern California, and olive rockfish occur 

 abundantly in both regions but, unlike the others, 

 are mostly restricted to Californian coastal waters 

 (Limbaugh 1955; Quast 1968a, d; Miller and 

 Geibel 1973). Because the Santa Barbara Channel 

 is near the northern limit of the San Diegan fauna 

 (Hubbs 1960; Quast 1968a), it harbors more cen- 

 tral Californian cool-water species (Ebeling et al. 

 1971; Ebeling, R. Larson, and W. Alevizon in 

 prep.). Hence all three species abound in Santa 

 Barbara kelp forests, and here, for example, the 

 olive rockfish may be better at capturing nekton, 

 thus reducing supplies for the other two. Off San 

 Diego, on the other hand, both rockfishes may 

 occur more sporadically (Quast 1968d) and com- 

 pete less intensely with the more numerous kelp 

 bass. Generally reduced planktivory off San Diego 

 may either reflect lower average plankton densi- 

 ties there (Smith 1971, 1974), or greater abun- 

 dances of larger, more preferred prey. 



Within the Santa Barbara area, habitat differ- 

 ences may affect prey availability and the species' 

 feeding habits. Like most areas of reef and kelp 

 (Feder et al. 1974; Miller and Geibel 1973), Naples 

 Reef may provide more refuges for larger prey. So 

 here, as suggested generally both from experi- 

 ments (e.g., Ivlev 1961) and theoretical models 

 (e.g., Schoener 1971; Estabrook and Dunham 

 1976), predators may concentrate on fewer 

 categories of larger, preferred prey in a greater 

 overall abundance of food. One-Mile Reef, on the 

 other hand, appears less intrinsically productive 

 because it is deeper than Naples Reef and supports 

 no giant kelp. So here larger prey may occur less 

 predictably and olive rockfish must switch to 

 plankton, including the tiniest of items, more fre- 

 quently. Santa Cruz Island reefs are even more 

 complex and productive than Naples Reef (Alevi- 

 zon 1975; D. Laur pers. commun.). Thus Santa 

 Cruz supports larger aggregations of olive rock- 

 fish, which tend more to segregate from equally 

 large aggregations of blue rockfish. 



Finally, food and space need not be the primary 

 factors that limit the sizes of the swdtch-feeder 

 populations. Severe storms, disease, and predators 

 may eliminate certain numbers of individuals. 

 Menge and Sutherland (1976) reviewed evidence 



269 



