FISHERY BULLETIN: VOL. 79, NO. 1 



400 



500 600 



WAVELENGTH (nm) 



700 



Figure 4. — Changes in downwelling submarine light through sunset near the surface at Santa Catalina Island during a phyto- 

 plankton bloom. Although there is relatively less blue light under these conditions, a blue shift at and following sunset is nonetheless 

 evident when compared with daylight under bloom conditions (Figure 2). P25, Pgf,, and P^j identify those wavelengths that divide the 

 number of visible photons into equal quarters. 



fire" of the ship's wake, the luminescent shroud 

 about porpoises running before the bow, and the 

 showers of sparks that trail fishes dashing below 

 the hull. At Santa Catalina Island, biolumines- 

 cence from plankton was visible in the water at all 

 times of the year, more so at some times than at 

 others. 



Most marine bioluminescent plankton emit 

 light in the blue region of the spectrum (Tett and 

 Kelley 1973). For example, light from Gonyaulax 

 polyedra and Noctiluca miliaris (which is repre- 

 sentative of most dinoflagellates) peaks near 475 

 nm, and more than half of the photons are emitted 

 below 500 nm (Hastings and Sweeney 1957; Nicol 



1958). Because of the skewed emission spectra 

 from these organisms (Figure 6), however, fishes 

 close to the luminescent source would absorb more 

 photons with visual pigments that have k^^^ val- 

 ues nearer 490 nm than 475 nm. 



In any event, the spectral quality of biolumines- 

 cence received by the fishes is modified by two 

 variables — distance the fishes are from the light's 

 source, and clarity of the intervening water. Be- 

 cause the water more effectively absorbs the 

 longer than the shorter wavelengths, a fish farther 

 from a target in clear water will receive relatively 

 more photons at the shorter wavelengths (Figure 

 6, upper panel). Water clarity, however, has an 



