FISHERY BULLETIN: VOL. 70, NO. 3 



The smaller parrotfishes had sought shelter ear- 

 lier. Gone now too are the triggerfishes Suffla- 

 men bursa (140: 109-164 mm) and Rhinecan- 

 thus rectangulus (142: 114-170 mm), as well as 

 the filefishes Pervagor spilosoma (85: 64-120 

 mm) and Cantherines sandivichiensis (116: 84- 

 132 mm) , all of which had remained close to the 

 substrate throughout their active periods dur- 

 ing daylight and early twilight. Because most 

 of these and many other diurnal species are not 

 especially numerous on all of the study areas, 

 often none are in view for long periods even 

 during those times of day when they are most 

 active; therefore, it would not have been mean- 

 ingful to record the last individual of each spe- 

 cies that was seen to take cover, as was done with 

 the ubiquitous Thalassoma duperrey and a few 

 other species treated in this report. This pro- 

 cedure is meaningful only with species whose 

 members are so numerous and widespread that 

 in all study areas some of them are always in 

 view during their active periods. Nevertheless, 

 these species, as described above, are only rarely 

 seen in exposed positions after the water column 

 has been vacated. 



Many sedentary diurnal fishes find shelter 

 during this period too. One suddenly realizes 

 that such species as the hawkfishes Paracirrhites 

 forsteri (139: 93-181 mm), P. arcatus (82: 49- 

 101 mm), and Cirrhitops fasciatus (76: 39-91 

 mm) are only occasionally visible in locations 

 where they are numerous during daylight. The 

 same is true of the blennies Exallias brevis (94: 

 70-106 mm) and Cirripectus variolosus (73: 66- 

 80 mm) . Relative activity in species that are at 

 least overtly inactive is difficult to quantify. 

 Nevertheless, after the nocturnal situation pre- 

 vails, about 30 min after the free-swimming fish- 

 es vacate the water column, these sedentary di- 

 urnal fishes rarely occur in exposed positions. 



THE EVENING INTERIM PERIOD 



When the last of those diurnal fishes swim- 

 ming above the coral abruptly descend to the 

 ocean floor, about 10 to 15 min after sunset, the 

 evening interim period begins. At the outset, 

 many diurnal fishes still mill about in pockets 

 among the coral, close to the substrate. Promi- 



nent among these are the medium-sized surgeon- 

 fishes, such as Acanthurus achilles, that were 

 prominent in the milling aggregations earlier. 

 In addition, a few of the larger surgeonfishes, 

 like A. dussumieri (340: 302-390 mm), still swim 

 slowly over the coral in small scattered schools, 

 but these do not diminish the prevailing quie- 

 scence. The closely related moorish idol, ZaTiclus 

 canescens (108: 74-137 mm), still swims in 

 groups of three or four, but close to the sub- 

 strate. The butterfishes, family Chaetodonti- 

 dae, often remain paired, as during midday, but 

 some already show colorations that are different 

 from those seen in daylight; these include Chae- 

 todon auriga (151: 132-160 mm), C. ornatissi- 

 mus (119: ^b-lAQ mm) , C . multicinctus (84: 78- 

 94 mm), and C. unimaculatus (85: 66-102 mm), 

 which become progressively less active and stay 

 close to the coraL Damselfishes too, including 

 Pomacentrus jenkinsi (89: 80-100 mm), and 

 Plectroglyphidodon johnstonianus (60: 39-70 

 mm), though generally solitary, remain active 

 close to coral and rock shelter at this time. The 

 chaetodontid C entropy gepotteri (80: 69-86 mm) 

 behaves much like these damselfishes. 



Into this situation of rapidly diminishing ac- 

 tivity among diurnal species, the nocturnal spe- 

 cies begin to emerge from the caves and crevices 

 of the reef, in which they have passed the day- 

 time. The first to appear is the cardinalfish 

 Apogon snyderi (96: 82-130 mm), which re- 

 mains close to the substrate, frequently mixing 

 with the diurnal species that are settling there. 

 A second cardinalfish, A. menesemus (114: 90- 

 134 mm) , soon follows its congener into the open. 

 The initial sightings of A. snyderi and A. mene- 

 semus moving away from shelter were recorded 

 on four and five evenings, respectively (Figure 

 4). 



Several minutes later, when the diurnal spe- 

 cies still in view are becoming more and more 

 quiescent, the first of the squirrelfishes, the rel- 

 atively large Holocentrus sammara (162: 128- 

 202 mm), appears. This event was recorded on 

 four evenings (Figure 5) . Throughout the day, 

 some individuals of both A. snyderi and H. sam- 

 mara hover in view at the entrances to their di- 

 urnal retreats; consequently, one must be thor- 

 oughly familiar with these fishes to recognize 



722 



