HOBSON and CHESS: TROPHIC INTERACTIONS 



bered categories are the same as those in which the 

 zooplankters are organized in Tables 1 and 2 and in 

 the text above. The few additional major categor- 

 ies include various nonplanktonic organisms that 

 some of these fishes had taken in small numbers. 

 Listed under each major category, according to 

 rank within that category, are the species and 

 species groups that are the actual prey of the fish. 

 Following most entries throughout the listing are 

 sets of three values in parentheses; these values 

 relate certain characteristics of the entry to the 

 food habits of the fish. (The values were derived 

 from calculations based only on fish that contained 

 identifiable material. Fish with empty guts or 

 containing only unidentifiable material were not 

 considered.) The first value in parentheses is the 

 percent of fish that contained the item(s); the 

 second value is the mean number of individuals of 

 the item(s) that were taken, and the third value is 

 the mean percent of the diet volume represented 

 by the item(s). Rank as prey was determined by a 

 ranking index, which is not shown, but which is the 

 product of the first and third values in 

 parentheses. 



Following the above format, the prey organisms 

 are: 



1. CALANOID AND CYCLOPOID COPEPODS (83: 44.4: 59.5) 



calanoids, including Acartia tonsa and Lahidocera sp. (81: 

 40.3: 54.9); cyclopoids, including Corycaeus sp. (38: 4.1: 4.6). 



2. GAMMARIDEAN AMPHIPODS (29: 0.4: 11.4) 



Batea transversa (18: 0.3: 7.6); unidentified fragments (11: 

 0.1:3.8). 



3. CARIDEAN LARVAE (20: 0.4: 3.2) 



unidentified species. 



4. MYSIDS(11:0.3:4.5) 



Acanthomysis sculpta (3: 0.1: 2.0);erythropinid sp. (3: 0.1: 

 0.5); unidentified fragments (7: 0.1: 2.0). 



5. CLADOCERANS (20: 1.1: 2.4) 



Evadnc sp. 



6. OTHER COPEPODS (18: 0.3: 2.2) 



unidentified monstrilloids. 



7. EUPHAUSID ADULTS AND JUVENILES (11: 0.1: 1.3) 



unidentified fragments. 



8. BRACHYURAN MEGALOPS (5: 0.1: 4.8) 



unidentified. 



9. HARPACTICOID COPEPODS (18: 0.4: 1.2) 



harpacticoid sp. A (7: 0.1: 0.7); PorcelUdium sp. B (5: 0.1: 0.2); 

 Porcellidium sp. A (2; 0.1: 0.1); unidentified fragments (5: 

 0.1:0.2). 



10. TANAIDS(10:0.2:2.4) 



Leptochelia dubia (7: 0.1: 1.2); unidentified fragments (3: 0.1: 

 1.2). 



11. REPTANTIAN ZOEA (11: 0.1: 1.3) 



unidentified. 



12. FISHES (5: 0.2: 2.0) 



unidentified larvae. 



13. ISOPODS (2: <0.1: 1.1) 



Paracercies sp. 



14. GASTROPODS (2: 0.4: 0.5) 



Tricolia sp. 

 1.5. EUPHAUSID LARVAE (2: <0.1: 0.1) 

 calyptopsis. 



16. CIRRIPEDIAN LARVAE (5:<0.1: <0.1) 



cypris. 



17. BRYOZOAN LARVAE (2: <0.1:<0.1) 



cyphonautes. 



Small juveniles took calanoid copepods as their 

 major prey from the time they began feeding at 

 sunrise until they ceased feeding at the end of the 

 day. In 10 specimens collected during May and 

 June (the only times for which calanoids in this 

 material were identified to species), about 22% of 

 the calanoids were Acartia tonsa, and although 

 the rest remained unidentified (except for a single 

 specimen of Lahidocera sp.), many probably were 

 immature individuals of this same species. 



A number of the prey listed above occurred only 

 in specimens collected during early morning. 

 These are: the gamaridean amphipods, the tan- 

 aids, the euphausids, the lone isopod, the megalops, 

 and all mysids except those in one individual (see 

 below). Most of these items were extensively 

 digested, in sharp contrast to the freshness of the 

 calanoids and other food materials in the early- 

 morning specimens. Clearly, they had been in the 

 guts for some time, probably since the previous 

 night. Nevertheless, judging from the empty guts 

 in most individuals of this size at daybreak it 

 would seem that nocturnal feeding is insignificant. 



Only later than about 30 min after sunrise did 

 the olive rockfish begin taking Evadne sp., but this 

 cladoceran then became a consistant component of 

 the diet for the rest of the day. Evadne is slightly 

 smaller and more transparent than the other prey 

 organisms, and to capture it the rockfish may need 

 more light. The only mysid taken during the day 

 was Acanthomysis sculpta, of which two in- 

 dividuals that appeared recently ingested were 

 found in one olive rockfish during midafternoon. 



INTERMEDIATE JUVENILES. -Individuals 

 between about 55 and 65 mm long were highly 

 inconsistent in so far as whether they fed by day or 

 by night (many did both). The nocturnal situation 

 among intermediate individuals is represented by 

 18 specimens (55-63 mm, x = 58) collected before 

 sunrise from open water during the hour before 

 first morning light, and also from developing 



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