HOBSON ET AL.: CREPUSCULAR AND NOCTURNAL ACTIVITIES OF CALIFORNIA FISHES 



specimens <100 mm long, 6 of 14 (102-114 mm SL, 

 X = 106.8) collected during the hour before dawn 

 contained prey, many of them fresh. The major 

 nocturnal prey, which included the gammarid 

 Batea transversa (2-4 mm), the caprellid Caprella 

 californica (8-14 mm), and the isopod Paracercies 

 cordata (1-6 mm), were organisms that rise into 

 the water column at night. We believe these prey 

 were captured in the water column because most 

 were in fish that had been aggregated in midwater 

 outside the seaward edge of a kelp forest. Perhaps 

 Bray and Ebeling (1975) found no evidence of noc- 

 turnal feeding because their sample comprised 

 mostly smaller fish. Significantly, the major or- 

 ganisms apparently taken in the water column at 

 night include the same species picked from the 

 surface of algae by day. 



Embiotocidae: Cymatogaster aggregata 



The shiner perch, which is even more variable in 

 its diel behavior than Brachyistius frenatus, has 

 two basic feeding modes: it captures zooplankton, 

 mostly crustaceans, in the water column, and it 

 captures organisms, again mostly crustaceans, 

 that are in, on, or close above a sandy bottom. The 

 planktivorous habit predominates among indi- 

 viduals smaller than about 65 mm SL and con- 

 tinues to be important throughout life, whereas 

 feeding on sand-dwelling forms becomes increas- 

 ingly important to individuals >65 mm SL until it 

 predominates among the largest individuals. The 

 planktivorous habit is diurnal, whereas feeding on 

 or close to a sandy bottom occurs during both day 

 and night, but mostly at night. 



Thus, the small juveniles are primarily day 

 feeders: of 23 (53-64 mm SL, x - 58.2) collected 

 during the afternoon, 12 (53%) contained food, the 

 major items being zooplankters (mostly copepods). 

 Only two (12%) also included prey that may have 

 been taken from the seafloor (gammarid frag- 

 ments). In comparison, only 2 of 17 (37-64 mm SL, 

 X = 46.5) collected during the hour before dawn 

 contained food: one (58 mm) contained just a few 

 cumacean fragments, but the other (54 mm) con- 

 tained a variety of sand-dwelling crustaceans, 

 some fresh, including the cumacean Cyclaspis 

 nubila (2-4 mm), the gammarid Acuminodeutopus 

 heteruropus (1-2 mm), and the tanaid Leptochelia 

 duhia (2-4 mm), along with sand. 



The changes in food habits that appear among 

 individuals >65 mm SL were similarly defined. Of 

 34 (67-110 mm SL, x = 91.8) collected during the 



afternoon, 27 (79%) contained food presumably 

 taken by day: 19 (70%) of these had fed exclusively 

 on zooplankton (primarily calanoid and cyclopoid 

 copepods and cladocerans), 4 (15% ) had taken only 

 sand-dwellers (primarily tanaids and gam- 

 marids), and 4 (15%) had fed on both zooplankton 

 and sand-dwellers in large numbers (combina- 

 tions of the above forms, with the two types sharp- 

 ly separated in the guts). In comparison, of 46 

 (66-120 mm SL,x = 85.9) collected during the hour 

 before dawn, 37 (80%) contained prey, many fresh, 

 that appeared for the most part to have been taken 

 at night. Significantly, all these prey were sand- 

 dwellers, the major forms being the cumacean 

 Cyclaspis nubila (2-4 mm), the gammarids 

 Acuminodeutopus heteruropus (1-2 mm) and Am- 

 pelisca christata (2-4 mm), the tanaid Leptochelia 

 duhia (3-4 mm), and the ostracod Euphilomedes 

 carcharondonta (1-2 mm), along with sand. 



Embiotocidae: Damalichthys vacca and 

 Embiotoca jacksoni 



Damalichthys vacca, the pile perch, and E. 

 jacksoni, the black perch, both appear to be strictly 

 diurnal feeders. During daytime, adults of D. 

 vacca feed primarily on moUusks and other heav- 

 ily shelled prey, whereas adults of E. jacksoni take 

 an exceptionally wide variety of benthic or- 

 ganisms, including polychaetes, mollusks, gam- 

 marids, caprellids, isopods, and mysids (Lim- 

 baugh 1955; Quast 1968). At night we observed 

 both species hovering close to the seafloor, gener- 

 ally in exposed positions. On the other hand, Ebe- 

 ling and Bray (1976) reported D. vacca "... scat- 

 tered in the water column at night." That neither 

 species feeds after dark is evidenced by the ab- 

 sence of fresh food in their guts at that time (Ebe- 

 ling and Bray 1976). 



Pomacentridae: Hypsypops rubicunda and 

 Chromis punctipinnis 



Although the Californian pomacentrids — H. 

 rubicunda, the garibaldi, and C . punctipinnis , the 

 blacksmith — are strictly diurnal fishes that re- 

 main relatively inactive in their nocturnal shel- 

 ters, they nevertheless remain alert throughout 

 the night. Hypsypops rubicunda, in fact, often ap- 

 pears restless as it moves in its shelter place. This 

 species is solitary during both day and night, and 

 its nocturnal shelter is a specific hole or crevice in 

 the well-defined territory that also includes its 



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