FISHERY BULLETIN: VOL. 79, NO. 1 



Kyphosidae: Girella nigricans 



The opaleye does not seem to feed extensively at 

 night, although our limited observations on this 

 point are somewhat ambiguous. This rather tenu- 

 ous opinion rests heavily on two points. First, the 

 species feeds largely on algae, and various or- 

 ganisms that live on algae — a diet generally indi- 

 cative of diurnal feeding (Hobson 1965, 1974; Viv- 

 ien 1973). Second, kyphosids generally have been 

 found to feed by day (e.g., Randall 1967). On the 

 other hand, observations of kyphosids at night 

 have indicated a variable condition. Kyphosus in- 

 cisor reportedly rests ". . .in sheltered, though not 

 confined, locations on the reef-top" in the Florida 

 Keys (Starck and Davis 1966), andK. elegans has 

 been noted to behave similarly in the Gulf of 

 California (E. S. Hobson unpubl. obs.). ButK. ele- 

 gans, at least, is alert in these shelters, and K. 

 cinerascens in Hawaii not only swims above the 

 reef at night, but may feed at this time as well 

 (Hobson 1974). The presence of G. nigricans ". . .in 

 holes or on the bottom . . ." at night led Ebeling and 

 Bray (1976) to consider it diurnal. We agree with 

 them even though we frequently saw this species 

 swimming in the water column after dark, espe- 

 cially in the kelp forest. 



Limited study of gut contents suggest reduced 

 feeding in some G. nigricans at night. One (201 

 mm) sampled among the rocks during the hour 

 before sunrise had an empty stomach, but the 

 stomach of another (264 mm) that was swimming 

 above the bottom at this time was 20% full. Sixty- 

 seven percent of the gut contents in this second 

 individual consisted of motile animals, including 

 gammarids, caprellids, carideans, and the gas- 

 tropod Tricolia sp., whereas only 10% consisted of 

 algae. This material, much of it fresh, differed 

 sharply from that in gut contents of individuals 

 that had been feeding by day. Benthic algae consti- 

 tuted 81% of the material in all 11 individuals 

 (173-255 mm SL, x = 206) that were collected 

 during the afternoon, and whose stomachs aver- 

 aged 75% full; essentially all other items in these 

 individuals were sessile organisms that encrust, 

 or live attached to, algae — principally bryozoans 

 and hydroids. 



Kyphosidae: Medialuna calif orniensis 



We consider the halfmoon primarily diurnal for 

 essentially the same tenuous reasons that led us to 

 this conclusion for G. nigricans: many of its close 



relatives reportedly are diurnal, as documented 

 above, and it feeds heavily on plants (Limbaugh 

 1955; Quast 1968), a diet widely associated with 

 diurnal foraging. Furthermore, we saw M. 

 californiensis , like G. nigricans, in the water col- 

 umn in far fewer numbers at night than during the 

 day. But although we saw G. nigricans in larger 

 numbers close to rocky substrata at night, we saw 

 M. californiensis, which was exceptionally 

 numerous in the kelp forests by day, only in sharp- 

 ly reduced numbers there after dark. Reporting a 

 similar situation in a kelp forest at Santa Barbara, 

 Ebeling and Bray (1976) observed about half as 

 many M. californiensis on their transect line at 

 night as during the day. They summarized their 

 nocturnal observations by stating that this species 

 ". . . often appeared to be more sensitive to our pres- 

 ence than were individuals of other species near 

 the bottom, and we cannot deny the possibility 

 that Medialuna feeds at night." Leading to much 

 the same position, our study of gut contents from 

 14 specimens (146-243 mm SL,x = 196) collected 

 during the afternoon (Hobson and Chess in prep.) 

 shows that this largely herbivorous species un- 

 questionably feeds by day, but leaves unanswered 

 whether or not it also feeds at night. 



Embiotocidae: Brachyistius frenatus 



Although the kelp perch is basically diurnal 

 throughout life, this characteristic can be some- 

 what variable. When less than about 100 mm SL it 

 feeds primarily on zooplankters in the water col- 

 umn, and as it grows larger it increasingly turns to 

 tiny prey — mostly crustaceans — that it picks 

 from vegetation (Hobson and Chess 1976). At night 

 it occurs in most of the same places that it occupies 

 by day, but is more numerous in midwater aggre- 

 gations fully exposed along the outer edges of the 

 kelp forests (Hobson and Chess 1976). Describing 

 the nocturnal condition of this species, Bray and 

 Ebeling (1975) noticed that it "...tended to hang 

 motionlessly along the kelp stipes or even in open 

 water" and added that it was "...quiescent at 

 night and easily caught with a small hand net . . . ." 

 They concluded that B. frenatus feeds ". . . mostly, if 

 not exclusively, during the day" — an opinion 

 based on study of gut contents from specimens 

 collected every 2 h throughout the night. But Hob- 

 son and Chess (1976) reported that while B. fre- 

 natus is primarily diurnal, larger individuals also 

 feed to a limited extent at night. In addition to the 

 data presented in that paper, all of which involved 



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