Pelagic Environment 



159 



more important they contained fishes which 

 had air bladders and thus were good sound 

 reflectors. Although neither squids nor 

 fishes were abundant in net hauls, others 

 may have been able to avoid capture. When 

 the benthograph was placed in operation, it 

 was hoped that the sound scatterers might 

 be identified from photographs and the ques- 

 tion resolved, but few large organisms were 

 photographed in the correct depth range 

 (Fig. 137). The small objects that scatter 

 light were found from counts on the photo- 

 graph negatives to be abundant in a broad 

 zone which included, but was much wider 

 than, the deep scattering layer. Even the 

 depth of maximum concentration of light- 

 scattering objects was diff'erent from the 

 depth of maximum concentration of sound- 

 scattering objects. More certain relation- 

 ships between echoes and photographed ob- 

 jects might be expected of an echo sounder 

 attached to a camera and suspended in the 

 deep scattering layer. Such a device de- 

 scribed by Johnson, Backus, Hersey, and 

 Owen (1956) has shown a good correlation 

 between echoes and the presence of small 

 fishes. 



Recently, precise measurements of light 

 generation at depth by Kampa and Boden 

 (1956) show the existence of flashes having 

 a wavelength of about 489 m/i, blue-green. 

 The maximum frequency and intensity of 

 the flashes are greatest within the deep 

 sound-scattering layer (Fig. 138), and the 

 color and intensity match that of individual 

 specimens of the euphausids that are known 

 to be present in the layer. Curiously, the 

 intensity of the flashes is 10 to 100 times the 

 intensity of general illumination with which 

 the euphausid is associated during its diurnal 

 cycle of movement. 



In summary, it seems likely that euphau- 

 sids and small fishes are major causes of the 

 layer, even though they and other organisms 

 are present in concentrations commonly less 

 than one per cubic meter of water. 



Bathypelagic Zone 



A small amount of work has been done 

 within the bathypelagic zone of the basins 

 off the coast through deep hauls of nets, 



dredging of basin floors, and photography. 

 In addition to collections by the Albatross 

 and Scripps Institution of Oceanography 

 prior to 1915 and some later unpublished 

 work, about 33 net hauls between 270 and 

 1300 meters have been made aboard R/V 

 Velero IV since 1949 with nonclosing hoop 

 nets 2 meters in diameter and 8 meters long. 

 These depths span the bottom of the meso- 

 pelagic and the top of the bathypelagic 

 zones (Hedgpeth, 1957). Crustaceans that 

 were recovered include mysid, euphausid, 

 and decapod shrimps, hyperiid and gam- 

 maridean amphipods, and copepods. Of 

 the 31 species of shrimps identified up to 

 1952, 13 were found only in hauls that 

 reached depths greater than 800 meters 

 (J. S. Garth, personal communication). 

 They include cosmopolitan, temperate 

 northern Pacific, tropical eastern Pacific, and 

 weak endemic elements. A summer peak 

 of abundance was indicated for some spe- 

 cies. As elsewhere, these crustaceans are 

 bright red, but because of high absorption 

 of red by sea water they appear at depth to 

 be black. 



Many deep-sea fishes (Fig. 139) were 

 obtained along with the crustaceans, per- 

 haps because the fishes feed on them. Most 

 common are Cyclothone spp. of the family 

 Gonostomatidae, six species of which are 

 known to occur in the region. At least 60 

 per cent of all specimens taken are of this 

 genus, and they were found at all depths 

 sampled (to 1300 meters). They are black, 

 slender, range from 2 to 8 cm in length, and 

 have small eyes. Next most abundant in 

 the bathypelagic zone is Lampanyctus leu- 

 copsarus, a lantern fish of the family Mycto- 

 phidae. Representatives of this family were 

 found by Tucker (1951) to be the most com- 

 mon fish in the deep sound-scattering layer 

 of the mesopelagic zone. Having phospho- 

 rescent organs, their black slender bodies 

 range up to 12 cm long. Third most com- 

 mon is Leuroglossus stilbius, a black and 

 silver herring-like fish of the family Argen- 

 tinidae which also reaches lengths as great 

 as 12 cm. Many other curious and bizarre 

 fishes have been found, but only in small 

 numbers. Few collections and studies have 

 been made of fishes living close to the bot- 



