FISHERY BULLETIN: VOL. 74, NO. 4 



1971). Similarity (Q is scaled from (no resem- 

 blance at all) to 1.0: 



C= 1.0 - V2 12\Pu - Pj, 

 I = 1 



where P,j = the proportionate abundance of 

 species i in day sample j, and P,,^ = that in night 

 sample k. 



Though the mid-water zone abounded with 

 fishes during the day, it appeared sparsely 

 populated at night (Table 4). Day-night similarity 

 within the mid-water zone was the least (C = 0.12) 

 for the four zones. Six of the 10 species recorded 

 from the mid-water zone at night were surf- 

 perches, while three of the remaining four were 

 rockfishes. Hyperprosopon argenteum accounted 

 for 62% of the total fish recorded in this zone. 

 Damalichthys vacca, along with Sebastes serra- 

 tioides and adult S. mystinus, were often seen 

 scattered in the water column at night. 



Although the suprabenthic zone underwent a 

 substantial reduction in fish abundance at night, 

 its day-night species similarity was the highest 

 (C = 0.67) for the four zones. During both day and 

 night, the suprabenthic zone was dominated by 

 surfperches. At night, surfperches comprised the 

 four most abundant species, accounting for almost 

 80% of the total fishes observed in the suprabenthic 

 zone (Table 4). Although Pacific electric rays 

 {Torpedo californica) were never recorded over the 

 transect lines, they were often encountered 

 nearby, swimming slowly and hovering above the 

 bottom (Bray, Hixon, and Ebeling unpubl. data). 

 Swell sharks {Cephaloscylliu m ventriosu m), whose 

 nocturnal activities were investigated by Nelson 

 and Johnson (1970), were occasionally seen swim- 

 ming just above the reef at night. 



Fish observed in the bottom zone increased from 

 7.4% of the total individuals recorded from all 

 zones during the day to 17.1% of the total at night 

 (Table 4). The zone's relatively low day-night 

 species similarity (C = 0.28) was due to variations 

 in numbers of the demersal ambusher-type 

 predators and increases in numbers of "resting" 

 surfperches. Among the ambusher-type species, 

 e.g., numbers of painted greenling, Oxylehius 

 pictus, decreased from 179 counted during the day 

 to only 6 at night, and numbers of two common 

 rockfishes increased: the black-and-yellow, S. 

 chrysomelas, almost doubled and the gopher, S. 

 carnatus, almost tripled (Table 4). 



At night, most fishes were observed in the 

 shelter zone. Although only 2% of the day total of 

 fishes were seen in holes and crevices, 50% of the 

 night total were observed there (Table 4). Day- 

 night species similarity was fairly low (C = 0.36), 

 largely because of the increase in numbers of 

 individuals of Chromis punctipinnis observed in 

 holes: from only 13 counted during the day to 610 

 counted at night (Table 4). Individuals of 

 Pimelomefopon pulchrum and S. mystinus were 

 also commonly seen in the shelter zone at 

 night. 



These counts of fishes inhabiting holes, 

 especially at night, may be conservative because 

 we could not completely census the numerous deep 

 holes and crevices along the transect line. This 

 problem certainly influenced our counts of in- 

 dividuals of 0. pictus and juvenile S. mystinus. 

 Nocturnal counts of both species were much lower 

 than those made during the day, and the in- 

 dividuals that were observed at night were invar- 

 iably hiding deep in holes. Subsequent nighttime 

 applications of small amounts of the anesthetic 

 quinaldine to holes that first appeared vacant 

 often yielded several 0. pictus and 5 to 20 juvenile 

 S. mystinus. Similar applications of this anes- 

 thetic during the daytime occasionally revealed 

 these fishes, but in far smaller numbers. 



The vertical positions of the 25 species of fishes 

 during the day and night are summarized in Table 

 4. Data on some species are fragmentary because 

 individuals of these species were rarely encoun- 

 tered along the transect line. However, general 

 observations made during hundreds of hours of 

 diving during both day and night tend to sub- 

 stantiate conclusions based on these data. For 

 example, we saw but two kelp bass along the 

 transect line at night, one in mid-water, the other 

 on the bottom. In surrounding areas, we saw many 

 individuals resting on the bottom, several in 

 mid-water, but very few in holes. Eighteen of 24 

 species recorded during the day were most com- 

 mon in the suprabenthic and mid-water zones 

 above the reef. Only the treefish, .S. serriceps, was 

 most common in the holes of the shelter zone. Of 

 the 23 species recorded at night 16 were most 

 common in contact with the reef, either in the open 

 positions of the bottom zone or in the holes of the 

 shelter zone. Only two species, Hyperprosopon 

 argenteum and S. serranoides, were most common 

 in the mid-water zone. 



The day-night differences in the activities of 

 many species involved considerable shifts among 



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