HOBSON ET AL.: CREPUSCULAR AND NOCTURNAL ACTIVITIES OF CALIFORNIA FISHES 



Figure 8. — a female Semicossyphus pulcher at rest on the seafloor at night, showing the typical pattern of its nocturnal hues. Its 

 exposed position is common in this and many other noctumally resting diurnal fishes in California. 



harbor the same fish as before, but this time posi- 

 tion No. 1 contained a small individual not seen 

 before. On the final return, position No. 5 once 

 more was occupied by what seemed to be the same 

 fish. Again, just one other position was filled — No. 

 6, which harbored the fish seen in position No. 9 on 

 the first night (recognized by a notch in its dorsal 

 fin), but which had gone unseen since then. Thus, 

 only one position, No. 5, sheltered a fish each time. 

 And contrary to what one might expect, of the nine 

 positions. No. 5 offered the least cover. It was sim- 

 ply a shallow depression on the reeftop where the 

 resting fish was largely exposed, and certainly 

 would not seem an effective shelter. 



Clinidae: Alloclinus holderi, Gibbonsia elegans, 

 and Heterostichus rostratus 



The three Californian clinids studied here — A. 



holderi, the island kelpfish; G. elegans , the spotted 

 kelpfish; andH. rostratus, the giant kelpfish — are 

 known to feed regularly by day, based on fresh food 

 in specimens collected during the afternoon (Hob- 

 son and Chess in prep.). But it is difficult to deter- 

 mine relative activity in these highly cryptic 

 fishes because they move so infrequently and, 

 therefore, often go unnoticed even when ftilly ex- 

 posed. Both A. holderi, which sits on rocks, and G. 

 elegans, which sits amid benthic algae, retire to 

 shelter at nightfall, as do various tropical clinids 

 (Starck and Davis 1966; Smith and Tyler 1972). 

 Heterostichus rostratus, on the other hand, often 

 hovers among columns of giant kelp during both 

 day and night (Figure 9). Our data comparing 

 relative feeding activity in H. rostratus between 

 day and night are limited, but indicate that day- 

 time feeding predominates. The one individual 

 (184 mm) collected during the hour before sunrise 



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