LOVE and EBELING: FOOD AND HABITAT OF THREE FISHES 



RESULTS 



Morphology, Size Groups, Gut Fullness 



Of the three species, the blue rockfish appeared 

 best adapted to eat a diverse array of small prey. It 

 has a shorter jaw (ca. 15% of SL) than the olive 

 rockfish and kelp bass (ca. 17%). It has about the 

 same number of gill rakers on the first arch as the 

 others (34-37); but has significantly smaller inter- 

 raker widths {X = 1.24 ±0.088 mm, 95% con- 

 fidence limits, n = 10) than the others pooled ix = 

 1.80 ±0.076, n = 20). Blue rockfish have a sig- 

 nificantly longer intestine (ratio, intestinal 

 length/SL of x = 1.41 ±0.147, n = 15) than either 

 kelp bass ix = 1.11 ±0.105, n = 18) or olive 

 rockfish (x = 0.807 ±0.098, n = 19). 



Tests justified comparing diets offish within the 

 151- to 300-mm SL size range, which included 82% 

 of all food-containing individuals (Table 1). 

 Within this range, only the median length of olive 

 rockfish from One-Mile Reef differed significantly 

 from the others (Kruskal-Wallace ranks location 

 test, P<0.05 including the One-Mile sample, 

 P>0.1 excluding it). Also (Figure 1), diets as ex- 

 pressed by frequencies of occurrence of prey types 

 were not significantly heterogeneous between 

 subgroups: largest chi-square value determined in 

 tests of the resulting 14 contingency tables of di- 

 mension two (presence or absence) by two (sub- 

 groups within this size range) = 2.31 (P>0.1). 



However, tests showed less justification for in- 

 creasing sample size by adding individuals from 

 outside the 151- to 300-mm size range (Figure 1). 

 Diets were often significantly heterogeneous be- 

 tween subgroups when either smaller (blue rock- 

 fish, olive rockfish) or larger (kelp bass) sizes were 

 included: 5 of 11 chi-square values determined in 

 tests of the resulting 11 contingency tables of di- 

 mension two (presence or absence) by three (sub- 

 groups both within and without the 151- to 

 300-mm range) were significant at P~ 0.05 or less. 



Scored stomach fullness in 151- to 300-mm 

 Naples Reef fish was about the same for all three 

 species: x = 2.72-2.75, an equivalent of about 46% 

 full. Intestinal fullness averaged somewhat great- 

 er: X = 2.76 (olive rockfish) to 3.00 (others). Blue 

 rockfish and olive rockfish in the smaller size 

 categories had fuller stomachs: x = 3.81-3.10, re- 

 spectively. Olive rockfish from One-Mile Reef had 

 less food in their stomachs ix = 2.15) but as much 

 food as the others in their intestines {x = 3.05). 



Intestinal contents usually resembled stomach 

 contents. 



Food 



Diets 



Blue rockfish ate mostly swimming, drifting, or 

 attached organisms in midwater under and about 

 the kelp canopy (Table 2, Figure 1). Tunicates, 

 hydroids, kelp, fish, and smaller planktonic prey 

 formed most of the fish's diet throughout the year. 

 Recognizable fish prey included juveniles of 

 pipefish, Syngnathus; blue rockfish; and C-O 

 soles, Pleuronichthys coenosus; and adults of 

 northern anchovy. Fish larvae made up but a 

 small part of the blue rockfish's diet. Pelagic 

 tunicates — the thaliaceans (salps) Salpa and 

 Doliolum and the larvacean Oikopleura — 

 constituted the largest volume of food consumed. 

 Among the relatively large numbers of small 

 plankters eaten, copepods ranked very low in vol- 

 ume, but relatively high in frequency of occur- 

 rence. Hydroids (especially Sertularia) ranked 

 high in volume consumed. The blue rockfish were 

 probably not merely ingesting hydroids to obtain 

 the caprellid amphipods that live there (Gotshall 

 et al. 1965), because caprellids were found along 

 with hydroids in only 2 of 20 stomachs. Some 73% 

 of the fish that contained kelp and other algae also 

 contained detached hydroids and encrusting bryo- 

 zoans (Membranipora). So most plant material 

 may have once borne epiphytic prey now detached. 

 And like tunicate tunics, algae per se was appar- 

 ently passed undigested, so fish probably eat 

 plants for the attached animals (Quast 1968d; 

 Bray and Ebeling 1975). 



Kelp bass foraged primarily in midwater, but 

 occasionally ate bottom organisms (Table 2, Fig- 

 ure 1). They ate mostly fish, which ranked first in 

 both total volume and frequency of occurrence. 

 Recognizable fish prey included juveniles of 

 rockfishes, pipefish, kelp greenling, Hexagram- 

 mos decagrammus, topsmelt, Atherinops affinis, 

 anchovy, and jack mackerel, Trachurus symmet- 

 ricus, and adults of anchovy and agonids. Kelp 

 bass ate no fish larvae and relatively less plankton 

 than did the other species. Thaliacean tunicates 

 (Salpa) contributed the largest volume of 

 plankton consumed; copepods and other small 

 crustaceans occurred at moderate frequency and 

 in fairly large numbers in a few individuals. Bass 

 ate relatively more substrate-oriented prey, with 



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