CREPUSCULAR AND NOCTURNAL ACTIVITIES OF 



CALIFORNIAN NEARSHORE FISHES, WITH CONSIDERATION OF 



THEIR SCOTOPIC VISUAL PIGMENTS AND THE PHOTIC ENVIRONMENT^ 



Edmund S. Hobson,^ William N. McFarland,^ and James R. Chess^ 



ABSTRACT 



Activities in 27 of the major southern Califomian nearshore fish species, with emphasis on trophic 

 relationships, were studied between 1972 and 1975 at Santa Catalina Island. Because these fishes 

 orient primarily by vision, they are strongly influenced by the underwater photic environment, which 

 we define with representative spectra. We center on crepuscular and nocturnal events, but also describe 

 daytime events for comparison. 



The species that feed mostly by day include Atherinops affinis, Paralabrax clathratus, Girella 

 nigricans, Medialuna califomiensis , Brachyistius frenatus, Cymatogaster aggregata, Damalichthys 

 vacca, Embiotoca Jacksoni, Chromis punctipinnis, Hypsypops rubicunda, Halichoeres semicinctus, 

 Oxyjulis califomica, Semicossyphus pulcher, Alloclinus holderi, Gibbonsia elegans, Heterostichus 

 rostratus, and Coryphopterus nicholsi. Those that feed mostly at night include Scorpaena guttata, 

 Sebastes atrovirens, S. serranoides (subadult), S. serriceps, Xenistius califomiensis, Seriphus politus , 

 Umbrina roncador, and Hyperprosopon argenteum . Those that show no clear diurnal or nocturnal mode 

 include Leiocottus hirundo and Pleuronichthys coenosus. 



Activity patterns tend to be defined less clearly in the warm-temperate fish communities of Califor- 

 nia than in fish communities of tropical reefs. Included are the twilight patterns of transition between 

 diurnal and nocturnal modes, which are considered to be defined by predation pressures. The lesser 

 definition of twilight patterns in California could mean reduced crepuscular predation there, but we 

 believe that Califomian fishes, too, have evolved under severe threats from crepuscular and nocturnal 

 predators. We suggest this is evidenced in the spectral sensitivities of their scotopic visual pigments, 

 which cluster around 500 nm — the best position for vision during twilight and at night in Califomian 

 coastal waters. 



Although the scotopic system dominates vision in dim light, the spectral sensitivities of the scotopic 

 pigments are poorly matched to the major forms of incident light at night — moonlight and starlight. 

 Rather, they match twilight and bioluminescence, which favor similar spectral sensitivities. We believe 

 this benefits these fishes most on defense. The match with twilight, when the low levels of incident light 

 shift briefly to shorter wavelengths, enhances vision during the crepuscular periods of intensified 

 threats from predators. And the match with bioluminescence permits fishes to react to threatening 

 moves in nocturnal predators by responding to luminescing plankton that fire in the turbulence 

 generated by these moves. 



Most fishes that live in southern Califomian 

 coastal waters orient by vision, and so are strongly 

 influenced by the cheiracteristics of underwater 

 light at different times of the diel cycle. Knowing 

 that these variations in light are accompanied by 

 differing behavior patterns in the fishes (Hobson 

 and Chess 1976; Ebeling and Bray 1976), we con- 

 sider here circumstances during twilight and at 

 night, when light is reduced and the fishes' 



'Contribution No. 45 from the Catalina Marine Science 

 Center, University of Southern California. 



^Southwest Fisheries Center Tiburon Laboratory, National 

 Marine Fisheries Service, NOAA, 3150 Paradise Drive, Tiburon, 

 CA 94920. 



^Section of Ecology and Systematics, Division of Biological 

 Sciences, Cornell University, Ithaca, NY 14853. 



scotopic (dim-light sensitive) visual systems are 

 operating (McFarland and Munz 1975c). A later 

 report will consider circumstances during day- 

 light. We relate the crepuscular and nocturnal ac- 

 tivities of the fishes and their scotopic visual pig- 

 ments to the spectral composition of light in their 

 warm-temperate habitat, and compare these rela- 

 tionships with the similar ties among activities, 

 visual pigments, and light among fishes in tropical 

 waters. 



We stress trophic relationships, because we con- 

 sider these the major forces shaping activity pat- 

 terns and related sensory systems in these fishes. 

 The species studied are among the more numerous 

 and readily observed in the nearshore warm- 

 temperate eastern Pacific Ocean. Our accounts of 



Manuscript accepted June 1980. 

 FISHERY BULLETIN; VOL. 79, 



No. 1, 1981. 



