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



- 100 



400 



500 600 



WAVELENGTH (nm) 



700 



Figure 5. — Underwater spectral distributions of moonlight, 

 starlight, and bioluminescence. Values for bioluminescence are 

 for Noctiluca miliaris, as given by Nicol (1958), at zero range. 

 Values for moonlight and starlight, based on measurements in 

 Munz and McFarland (1977), are for down welling light at zero 

 range from a flat spectral reflector at a depth of 3 m in water 

 equivalent to typical conditions at Santa Catalina Island ( Jerlov 

 1968, Coastal Type 1). 



even greater effect than distance on the attenua- 

 tion and spectral modification of submarine light. 

 In the typical water we encountered at Santa 

 Catalina, for example, there was a fairly high 

 transmission of light between 425 and 575 nm. As 

 light travels from a source like N. miliaris under 

 these conditions its radiance attenuates slowly 

 and its spectrum shifts only slightly (Figure 6, 

 middle panel). On the other hand, as the same 

 light travels through water heavily loaded with 

 phytoplankton it attenuates rapidly and there is a 

 marked and continuous spectral shift toward the 

 green (Figure 6, lower panel). 



ACTIVITY PATTERNS AND 

 VISUAL PIGMENTS IN FISHES 



Because the photic environment contrasts 

 sharply between day and night, those visually 

 orienting fishes that are adapted to diurnal condi- 

 tions should be less suited to feed after dark, while 

 those adapted to nocturnal conditions should be 

 less suited to feed by day. This expectation has 

 been supported in studies of temperate species, 

 both marine (Hobson and Chess 1976; Ebeling and 

 Bray 1976) and freshwater (Emery 1973; Helfman 

 1979), just as it has in studies of marine fishes in 



400 500 600 



WAVELENGTH (nm) 



Figure 6. — Attenuation and spectral distribution of light emit- 

 ted by Noctiluca miliaris over distance in water of differing 

 clarities. The three panels of the figure each represent a different 

 water type (clarity), as defined by Jerlov (1968): Type lA (upper) 

 is equivalent to clear tropical seas; Coastal Type 1 (middle) is 

 equivalent to typical conditions at Santa Catalina Island; and 

 Coastal Type 7 (lower) is equivalent to conditions of heavy 

 phytoplankton bloom at Santa Catalina. The heavy outer curve 

 in each panel represents the light emitted by A'^. miliaris (left 

 axes) at zero range, and so is the same in each water type. The 

 inner curves in each panel represent relative attenuation of light 

 at distances ( in meters ) indicated by the accompanying numbers. 

 The broken line in each panel represents the transmission 

 values/meter (right axes) for that water type, as given by Jerlov 

 (1968). 



the tropics (Hobson 1965, 1968a, 1972, 1974, 1975; 

 Starck and Davis 1966; Collette and Talbot 1972; 

 Smith and Tyler 1972; Vivien 1973). Thus, in con- 

 sidering the impact of diel variations in the photic 

 environment it is meaningful to distinguish diur- 

 nal and nocturnal species, even though some near- 

 shore fishes feed at all hours — many by changing 

 their food or tactics between day and night, e.g., 

 the serranids Epinephelus labriformis in the Gulf 

 of California (Hobson 1968a) and E. merra in the 

 Indian Ocean (Harmelin- Vivien and Bouchon 

 1976) and the mullid Parupeneus bifasciatus in 

 Hawaii (Hobson 1974). 



