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



Table 3. — Some southern Califomian fishes that feed day and 

 night, with the spectral absorbance maximum (X^jax' o^ P'8" 

 ments extracted from their retinae. 



'See Table 1, footnote 1. 



rare occasions that feeding was observed, this fish 

 moved only a few centimeters to snatch an object 

 in the sand. Eight specimens (130-196 mm SL, jc = 

 177) were collected from a variety of habitats dur- 

 ing the afternoon. Six (75%) contained food in 

 their stomachs, with the predominant prey being 

 the polychaetes Glycera capitata (30-85 mm), 

 Lumberineris sp. (20-90 mm), and terrebellid ten- 

 tacles. One had taken the gammarid Ampelisca 

 cristata (12 mm), and one a holothurian (17 mm). 

 Comparable data on nocturnal feeding was ob- 

 tained from eight specimens (66-194 mm SL, x = 

 136) collected during the hour before dawn. Again, 

 six (75%) contained food in their stomachs, with 

 polychaetes — Glycera sp. (35 mm), Nothria stig- 

 matis (8 mm), and a terrebellid (30 mm) — the 

 major prey, though less so than during the day. 

 Gammarids, especially Ampelisca cristata (2-6 

 mm) were important to these nocturnal individu- 

 als, as was the clam Solemya valvus (8-10 mm). 

 But these differences in prey selection between 

 day and night may relate to fish size rather than to 

 time of feeding: two Leiocottus hirundo collected 

 during the night were smaller (66 and 84 mm) 

 than any taken by day, and it was these that had 

 preyed mostly on gammarids. Aside from these 

 minor differences in food composition, feeding 

 habits appear similar day and night: stomachs of 

 the day feeders averaged 75% full, and contained x 

 = 4.2 items, compared with an average of 69% full 

 andic = 4.8 items for the night feeders. 



Pleuronectidae: Pleuronichthys coenosus 



The C-0 turbot rests immobile on sandy sub- 

 strata at all hours of day and night — usually ex- 

 posed but sometimes under a thin layer of sedi- 

 ment. Often it occurs in the same habitat as L. 

 hirundo, but more so than the cottid it ranges into 

 regions of open sand, where its highly variable 

 coloration often matches the surroundings. We 

 have observed feeding only in daylight, when typi- 

 cally this species rests motionless, with body 



somewhat elevated on dorsal and anal fins and 

 head poised above the substratum (Figure 12). Its 

 mobile, closely set eyes are oriented vertically on a 

 bony ridge, and function almost as if set in a tur- 

 ret. This arrangement permits the fish to scan the 

 seafloor close at hand, probably for moving sedi- 

 ments or other signs of prey that aire just below the 

 surface. Occasionally we have seen individuals 

 that had been immobile in one spot for some time 

 move a meter or so across the seafloor, pause for a 

 moment, and then drive their heads into the sedi- 

 ment. Usually we were unable to see what they 

 had taken, but daytime quarry were identified in 

 the 11 specimens that contained food out of 14 

 (161-212 mm SL, x = 186) collected from sandy 

 substrata during the afternoon (stomachs aver- 

 aged 47% full). The major prey were polychaetes, 

 especially terrebellid tentacles. Although we did 

 not observe feeding at night, prey were identified 

 in all 11 specimens (159-220 mm SL, x = 183.5) 

 collected during the hour before dawn (stomachs 

 averaged 72% full). Again, polychaetes, especially 

 terrebellid tentacles, predominated. Clearly its 

 trophic relationships are similar to those of L. 

 hirundo, except that it may be more able to feed at 

 night. 



DISCUSSION 



Events during twilight and at night in Califor- 

 nian marine habitats can be compared with 

 equivalents on tropical reefs. Tropical activity 

 patterns have been described (Hobson 1965, 1968a, 

 1972, 1974; Starck and Davis 1966; Collette and 

 Talbot 1972; Smith and Tyler 1972; Vivien 1973), 

 as has scotopic vision in tropical fishes (Munz and 

 McFarland 1973). Below we relate our findings 

 with Californian coastal fishes to these and other 

 studies made elsewhere. First we consider crepus- 

 cular and nocturnal activity patterns and then 

 scotopic spectral sensitivity, first in relation to 

 ambient light, and then to bioluminescence. 



Activity Patterns 



In relating diel activity patterns of fishes in 

 Californian waters near Santa Barbara to fishes 

 on tropical reefs, Ebeling and Bray (1976) referred 

 to the Californian species as "kelp-bed" fishes. We 

 assume they implied a broad concept of this term 

 that includes fishes sometimes in kelp forests, but 

 more characteristic of other habitats. This is be- 

 cause the tropical side of their comparison (which 



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