HOBSON and CHESS: TROPHIC INTERACTIONS 



"Queenfish school in tightly packed aggregations 

 over sandy bottom." 



Four of five individuals (124-171 mm, x = 148) 

 collected shortly after they had arrived in the 

 study area at nightfall had an empty gut, and the 

 fifth contained just a single freshly ingested 

 shrimp (unidentified). We conclude that these 

 individuals had passed the previous day without 

 feeding. The evidence further suggests they do 

 not feed while en route from daytime schooling 

 sites to their feeding ground in the study area. 



All 31 specimens (114-193 mm, x = 151) sampled 

 in the study area at night, later than 3 h after 

 sunset and before first morning light, had material 

 in their guts— much of it fresh. All prey belonged 

 to groups known to occur in the water column. 

 Limbaugh (1955) reported that this species feeds 

 on "small free-swimming crustaceans and fish." 

 Below are ranked the species and species groups 

 taken as prey by this fish. 



1. MYSIDS (84: 22.5: 44.7) 



Siriella pacifica (84: 21.0: 39.6); Acanthomysis sculpta (52: 

 1.4: 5.0); erythropinid sp. (6: 0.1:<0.1). 



2. GAMMARIDEAN AMPHIPODS (89: 16.0: 21.6) 



Batea transversa (84: 15.6: 20.2); Ampelisca sp. (9: 0.2: 0.3); 

 lynsianassid spp. (6: 0.1: 0.2); Ampithoc sp. (3: 0.1: 0.1); 

 unidentified (3: <0.1: 0.8). 



3. POLYCHAETES, SWIMMING (31: 0.8: 21.8) 



Epitokous nereids (22: 0.7: 18.4); unidentified (9: <0.1: 3.4). 



4. CARIDEAN ADULTS AND JUVENILES (44: 0.7: 5.9) 



Eualus herdmani (28: 0.4: 2.0); Hippolyte clarki (19: 0.3: 2.0); 

 unidentified (3: <0.1: 1.9). 



5. ISOPODS (34: 0.7: 3.6) 



Paracercies sp. (22: 0.5: 1.7); gnathiid juveniles (13: 0.1: 0.2); 

 Limnoria sp. (3: 0.1: 1.1); Excorallana kathae (3: <0.1: 0.5); 

 Cirolana harfordi (3: <0.1: 0.1). 



6. FISHES (6: 0.6: 1.4) 



scales. 



7. NEBALIACEANS(6:0.1:0.2) 



Nebalia pugettensis. 



8. OSTRACODS(13:0.3:0.2) 



Vargula americana (6: 0.1: <0.1); Cycloeberis lobiancoi (3: 

 0.1: <0,1); Parasterope sp. A (3: 0.1: <0.1). 



9. CARIDEAN LARVAE (3: <0.1: 0.3) 



unidentified. 



10. BRACHYURAN MEGALOPS (3: <0.1: 0.2) 



unidentified. 



11. EUPHAUSID ADULTS AND JUVENILES (3: <0.1: <0.1) 



unidentified. 



12. CUMACEANS (3: <0.1: <0.1) 



Cyclaspis nuhila. 



A single small juvenile queenfish, 38 mm long, 

 was collected on 2 November shortly before first 

 morning light as it swam alone close over the sand. 

 Its full gut contained mysid Siriella pacifica, 

 gammaridean amphipod Batea transversa, and 

 isopod Limnoria sp. All of these forms are also 



prey of larger queenfish, but those taken by this 

 small individual were less than half the size of prey 

 routinely taken by the larger fish. 



Material that we collected at La Jolla in 1971 

 included some information on smaller juveniles. 

 Ten individuals (10-27 mm, x = 19) were collected 

 on the same day during the hour before first 

 morning light-all from the stomachs of larger 

 individuals of their own species. Of these, only the 

 two largest, 23 and 27 mm, contained prey of the 

 types taken by larger conspecifics: mysids and 

 gammaridean amphipods constituted 99% of the 

 diet of these two, with calanoid copepods repre- 

 senting the remainder. In contrast, calanoid 

 copepods were the major prey of the seven smaller 

 individuals (in six, 80% of the total diet). Fish 

 larvae (in one, 11% of the total diet), and cladocer- 

 ans (in one, 9% of the total diet), constituted the 

 rest. These limited data indicate that the 

 queenfish, like the olive rockfish above, changes as 

 it grows from a diet of copepods to one of mysids 

 and other plankters that appear after dark. The 

 queenfish, however, seems to make the change at a 

 smaller size, perhaps because it has a larger mouth. 

 Moreover, the data fail to show that the queenfish, 

 like the olive rockfish, feeds by day when subsist- 

 ing on copepods. 



Hyperprosopoti argenteutn— walleye surfperch 



The walleye surfperch, which can grow to 304 

 mm (Miller and Lea 1972), consistently schooled 

 during the day in about 2 to 5 m of water over sand 

 at the edge of the forest at the head of Fisher- 

 men's Cove. Usually these schools included 20 to 

 more than 100 closely spaced individuals. Members 

 of these schools appeared inactive, an impression 

 supported by the eight empty guts found in nine 

 individuals (115-173 mm, .f = 140) taken during 

 midafternoon (and the ninth contained only 

 well-digested fragments). Presumably describing 

 the daytime situation throughout southern 

 California, Limbaugh (1955) stated: "They school 

 in an aggregate cloud . . . over sand patches among 

 rocks." 



The schools dispersed at nightfall, and many 

 individuals spread along the seaward edge of the 

 forest at the perimeters of the cove. They swam 

 individually (Figure 10) or in small groups 1 to 3 m 

 above the bottom, usually over sand within a few 

 meters of, but sometimes within, the forest. Of the 

 35 (60-151 mm, x = 111) collected in the study area 

 between 4 h after sunset and daybreak, only one 



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