forest. The sea floor in this region is sand, and lies 

 under more than 30 m of water. Because black- 

 smiths habitually settled among rocks at night, 

 the offshore feeders migrated to resting areas 

 inshore at day's end. At the migration's peak, 

 groups of 100 or more blacksmiths spaced perhaps 

 50 m apart streamed along established routes. 



As the migrators swam between feeding 

 grounds and shelter areas, they passed among 

 many other blacksmiths, most of which were 

 actively feeding and which gave the migrators no 

 overt notice. Most of the blacksmiths in the vicin- 

 ity of the study area were nonmigrators that 

 found nocturnal shelter among rocks lying below 

 their mid-water feeding grounds. 



Most of the blacksmiths within the forest bor- 

 dering the study area began descending toward 

 the sea floor by sunset, and by 35 min after sunset 

 the vast majority had taken shelter among the 

 rocks. They rested here throughout the night, and 

 their lack of feeding during this period is indicated 

 by the empty guts we found in all 11 individuals 

 (111-143 mm, .r = 122) collected among rocks 

 during the 2 h immediately before first morning 

 light. 



In the morning, blacksmiths among the rocks 



FISHERY BULLETIN: VOL. 74, NO. 3 



became noticeably active about 40 min before 

 sunrise. They began to rise among the kelp 

 columns about 25 to 30 min before sunrise, and to 

 feed about 5 to 10 min later. At about the same 

 time that blacksmiths within the forest were 

 rising into the water column, the migrating in- 

 dividuals streamed along their courses to the 

 ofi'shore feeding grounds, reversing the courses 

 they had followed inshore the night before. 



DISCUSSION 



Trophic relationships among the fishes and 

 zooplankters near shore at Santa Catalina Island 

 diff"er strikingly between day and night (Table 9), 

 broadly paralleling the situation described earlier 

 in the water column above tropical reefs (Hobson 

 1965, 1968, 1972, 1973, 1974). This section discusses 

 these difi'erences and their evolutionary 

 implications. 



The Mid-Waters in Daylight 



Zooplankters populating the nearshore water 

 column at Santa Catalina during the day- 

 including radiolarians, cladocerans, copepods, and 



Table 9.- Percent of each fish species that took prey in each major food category. 



594 



