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Crepuscular and Nocturnal Activities of Californian Nearshore Fishes, with Consideration of Their Scotopic Visual Pigments and the Photic Environment'

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Crepuscular and Nocturnal Activities of Californian Nearshore Fishes, with Consideration of Their Scotopic Visual Pigments and the Photic Environment' CREPUSCULAR AND NOCTURNAL ACTIVITIES OF CALIFORNIAN NEARSHORE FISHES, WITH CONSIDERATION OF THEIR SCOTOPIC VISUAL PIGMENTS AND THE PHOTIC ENVIRONMENT' EDMUNDS. HOBSON?WILLIAM N. MCFARLANDPAND JAMESR. CHESS' ABSTRACT Activities in 27 of the major southern Californian nearshore fish species, wth emphasis on trophic relationships. were studied between 1972 and 1975 at Santa Catalina Island. Because these fishes onent pnmarily by vision, they are strongly influenced by the underwater photic environment, which wedefine with representative spectra. Wecenteron crepuscular and nocturnal events, but also describe daytime events for comparison. The species that feed mostly by day include Athennops affrnis, Paralabrax clathratus, Girella nigrrcans, Medialuna calrfornrensrs. Brachyrstrus frenatus, Cymatogaster aggregata, Damalrchthys uacca. Embiotoca jacksonr, Chromis punctiprnnrs. Hypsypops rubtcunda, Halrchoeres semicrnctus, Oxyjulrs calrfomrm, Semrcossyphus pulcher. Alloclinus holderr, Gibbonsra elegans. Heterostrchus mstratus, and Coryphopterus nrcholsc. Those that feed mostly at night include Scorpaena guttata. Sebastes atroutrens, S.sermnordes I subadult),S serriceps, Xenistius californiensrs. Seriphus polrtus. Umbrina roncador. and Hyperprosopon argentrum. Those that show no clear diurnal or nocturnal mode include Lerocottus hrrundo and Pleuronrchthys 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 twlight patterns in CalifoAia could mean reduced crepuscular predation there, but we believe that Californian 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 Californian 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 twlight, when the low levels of incident light shift bnefly to shorter wavelengths, enhances vision dunng the crepuscular periods of intensified threats from predators And the match wth 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 Californian scotopic (dim-light sensitive) visual systems are coastal waters orient by vision, and so are strongly operating (McFarland and Munz 1975~).A later influenced by the characteristics of underwater report will consider circumstances during day- light at different times of the diel cycle. Knowing light. We relate the crepuscular and nocturnal ac- that these variations in light are accompanied by tivities of the fishes and their scotopic visual pig- differing behavior patterns in the fishes (Hobson ments to the spectral composition of light in their and Chess 1976; Ebeling and Bray 1976), we con- warm-temperate habitat, and compare these rela- sider here circumstances during twilight and at tionships with the similar ties among activities, night. when light is reduced and the fishes' visual pigments, and light among fishes in tropical waters. We stress trophic relationships, because we con- 'Contribution No. 45 from the Catalina Marine Science sider these the major forces shaping activity pat- Center. Cniversitv of Southern California. 'Southwest Fisheries Center Tiburon Laboratory, National terns and related sensory systems in these fishes. Manne FisheriesService. NOAA, :3150 Paradise Drive.Tiburon. The species studied are among the more numerous CA 94920. and readily observed the nearshore warm- 5ection of Ecology md Systematics. Division ot B~oIoq~caI In Sciencw..Coi-nell L!niversity* lthaca. NY l4HS3 temperate eastern Pacific Ocean. Our accounts of .Manuscript accepted June 1980 1 FISHERY IIULLETIN VOL. 79. No 1. lYHl FISHERY BULLETIN VOL 79. NO 1 their activities cover observations over 15 yr in a cosine receptor head and calibrated in photons southern California-from San Diego north to per square centimeter per nanometer per second, Point Conception-but our more detailed obser- draws a quantal irradiance spectrum. Radiance of vations, along with the light measurements and the backlighting along a particular line of sight analysis of visual pigments, refer to Santa was measured by restricting the angle of view of Catalina Island (lat. 33"28 ' N, long. 118"29'W),35 the receptor head to a narrow cone (ca. 0.008 km from the mainland (Figure 1). Here the water steradians). Usually radiance was determined is consistently warmer and more transparent than along the zenith, horizontal, and nadir lines of on the adjacent mainland; during our study sur- sight. face temperatures ranged between about 11' and Because we were interested in comparing the 20" C, and underwater visibility generally ex- spectral distribution of submarine light for differ- ceeded 10 m. Thus, when related to comparable ent water conditions and along different lines of data collected earlier in the tropics (Hobson 1968a, sight, results have been normalized and are pre- 1972,1974;Munz and McFarland 1973; McFarland sented in terms of relative number of photons. The and Mum 1975a), these results offer a conserva- light levels that occur at twilight were beyond the tive measure of differences between warm- spectroradiometer's sensitivity for measurement temperate and tropical habitats. of spectral radiance. At twilight, therefore, spec- tral irradiance and not spectral radiance was METHODS measured. Irradiance data are reported in terms of absolute numbers of photons. Determining the Spectral Composition of To facilitate comparisons, several of the spectral Submarine Sunlight curves were indexed by calculating their APSOval- ues (Mum and McFarland 1973; McFarland and The spectral distribution ofsubmarine light was Munz 1975a). The AP5o value represents the measured with a Gamma 3000R spectroradiome- wavelength within the visible spectrum (400-700 ter4 mounted in an underwater housing (Munz nm) that halves the total number of photons under and McFarland 1973). The instrument, fitted with a spectral curve. Because underwater light is usu- ally homochromatic and fairly symmetrical in dis- 4Reference to trade names does not imply endorsement by the tribution, APSOprovides a useful single index to a National Marine Fisheries Servm. NOAA. spectrum. FIGURE1 -The study area in southern California Santa Cdtalina Island was the site of detailed observations. includ- - ing light measurements and analysis of visual pigments in fishes i ".,.."pW +- 32"L 8 IOUCTERS i i- 7 HOBSON ET AL. CREPUSCULAR AND NOCTURNAL ACTIVITIES OF CALIFORNIA FISHES Determining Activity Patterns in Fishes each retinal extract was homogeneous or con- tained more than one visual pigment. Pigment Our accounts of activity patterns in the fishes analysis was assisted by a computer program stem from direct underwater observations and (Munz and Allen 1968) designed to test for from study of gut contents. The underwater obser- homogeneity and also to characterize each visual vations were made using scuba and by snorkeling pigment by estimation of the wavelength of peak during all hours of day and night. The gut contents absorbance (Anax). Generally, the major photo- were from fishes speared at all hours of day and labile component in a vertebrate retinal extract is night, but primarily during late afternoon and the rod visual pigment, and the minor compo- within 2 h before first morning light-times nent(s) is the cone visual pigment(s) (Mum and which best distinguish diurnal and nocturnal McFarland 1975; McFarland and Mum 1975133. habits. To study the gut contents, the digestive Thus, in each retinal extract from the Catalina tract of each fish specimen was removed im- samples the dominant pigment is considered the mediately after collection and preserved in a 10% scotopic (or rod) visual pigment. formaldehyde solution. Analysis under a binocu- lar dissecting scope was performed later in the UNDERWATER PHOTIC ENVIRONMENT laboratory. We note in this report only major food items that we believe might add insight to our Coastal waters characteristically absorb light of accounts of diel activity patterns. More detailed shorter wavelengths than do oceanic waters be- accounts of the food habits are given elsewhere cause they contain more dissolved organic matter. (Hobson and Chess 1976; in prep.). All mea- They also scatter more light due to higher con- surements of fish size are of standard length (SL). centrations of suspended particulate matter. As a Although our accounts center on crepuscular and result, they transmit light of longer wavelengths, nocturnal events, we describe enough of what and, therefore, under a midday sun appear blue- happens in daylight to consider these events in the green, rather than blue like the open sea (see Jer- context of diel patterns. lov 1968 for classification of water types). Starting with these well-established facts, we attempted to Determining
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