FISHERY BULLETIN: VOL. 70, NO. 3 



the reef, directly below their midwater feeding 

 grounds. 



Just as they do in the evening, many smaller 

 herbivores, including the surgeonfishes Zebra- 

 soma flavescens and Ctenochaetiis strigosiis, as 

 well as the parrotfish Scarus sordidus, migrate 

 from one area to another, but the patterns are 

 not yet defined. Again, the picture is obscured 

 by the many other individuals of these same spe- 

 cies throughout the study areas that do not join 

 these migrations. Thus, as in the evening, it 

 remains unknown just what sort of redistribu- 

 tion most of these fishes achieve. Nevertheless, 

 the patterns seem to relate to the transition to- 

 ward the diurnal situation. 



Ascent of the Plankton-Feeding Damselfishes 



Adults of the larger plankton-feeding damsel- 

 fishes, Ahudefduf ahdominalis, Chromis ovalis, 

 C. verater, and Dascyllus albisella, join the surge 

 of diurnal fishes that rise into the water column 

 10 to 15 min before sunrise. Because they all 

 ascend above the reef at about the same rate, 

 the most readily observed, D. albisella, is repre- 

 sentative. On five mornings, stationed in one 

 location where the water was 8 m deep, I noted 

 when a particular aggregation of D. albisella 

 was clear of cover, and then as it gradually 

 ascended into the water column, I estimated 

 when it had attained levels of 3 m, and (on three 

 mornings) 5 m above the reef (Figure 9). 



The smaller plankton-feeding damselfishes 

 Chromis leucurus and C. vanderbilti rise above 

 the reef later than do these larger species. On 

 nine mornings, at a variety of locations, I noted 

 when the first individual of C. leucurus moved 

 out away from shelter (Figure 10). These fish 

 remained in about this position, solitary and with 

 shelter close at hand, for some time; at 15 min 

 after sunrise they had moved a little farther 

 from shelter, but otherwise their position was 

 unchanged. C. vanderbilti follows an even later 

 schedule. On the one occasion that it was re- 

 corded, solitary individuals first appeared close 

 to shelter at 1 min after sunrise, and 11 min 

 later had just begun to aggregate in pockets 

 among the rocks. 



15 10 5 5 10 



TIME RELATIVE TO SUNRISE (min) 



Figure 9. — Ascent of an aggregation of Dascyllus al- 

 bisella into the water column during morning twilight. 

 A. When the aggregation was first clear of cover above 

 the reef on five mornings. B. When the aggregation 

 had risen to 3 m above the reef on five mornings. C. 

 When the aggregation had risen to 5 m above the reef 

 on three mornings. For explanation of symbols, see 

 legends for Figures 2 and 4, except that this figure 

 represents morning events. 



Emergence of Other Diurnal Fishes 



Throughout the time that the diurnal fishes 

 noted above are resuming activity on the reef, 

 the many sedentary diurnal fishes become in- 

 creasingly evident, including the hawkfishes 

 Paracirrhites forsteri, P. arcatus, and Cirrhitops 

 fasciatus and also the blennies Exallvas brevis 

 and Cirripectus variolosus. These begin moving 

 out from shelter during the interim period, but 

 so unobtrusively that their initial appearance 

 usually goes unnoticed. 



When the milling assemblages and migrating 

 schools dominate the scene, additional fishes be- 

 come active close among the rocks and corals, 

 including the triggerfishes Sufflamen bursa and 

 Rhinecanthus rectangulus, as well as the file- 

 fishes Cantherines sandwichiensis and Pervagor 

 spilosoma. These too, being scattered and rel- 

 atively inconspicuous, often go unnoticed at first 

 appearance. 



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