DEEP OBSERVATIONS OF ANCHOVY 

 AND BLUE SHARKS FROM DEEPSTAR 4000 



Visual observations from manned deep-submer- 

 sibles have recently contributed to the knowledge 

 of the vertical distribution of marine organisms. 

 Prior to the introduction of these craft, vertical 

 distribution patterns were established using 

 sampling gear such as nets. This was gener- 

 ally sufficient in the case of the smaller, easily 

 captured forms since many of the nets used in 

 these studies could be opened and closed at pre- 

 determined depths so that selected strata would 

 be sampled exclusively. In the case of the larger, 

 more active fishes, however, knowledge of their 

 depth ranges has been mostly speculative. Sam- 

 pling of these animals has normally been accom- 

 plished using commercial fishing gear which is 

 generally indiscriminate with respect to the 

 depth of capture. This has been true of the two 

 species in question, the northern anchovy, En- 

 graulis mordax Girard, and the blue shark, Pri- 

 onace glauca (Linnaeus). 



One method used to establish the depth of an- 

 chovy schools has been to locate them with echo 

 sounders during the day when they are deep, 

 then remain over them until they rise to the 

 surface at night. Once the schools are at the 

 surface, identification can be made with mid- 

 water trawls. Common daytime depths of these 

 schools are between 140 and 220 m (personal 

 communication with K. F. Mais, California De- 

 partment of Fish and Game). Information on 

 vertical distribution of blue sharks has been re- 

 ported by Strasburg (1958). Analysis of long- 

 line fishing data from the central Pacific showed 

 that these sharks were often captured on the 

 deepest hooks. Although the exact depth of the 

 hooks at the time of capture was not known, the 

 approximate depths were in the 110-150 m 

 range. This report, then, should serve as a vis- 

 ual verification of this previous information. 



Dive 502 of the submersible Deepstar 4000 

 was made on 9 November 1968 at lat 32°26'N, 

 long 117°23'W, west of the Coronado Islands. On 

 the way to the dive site from San Diego aboard 

 the mothership Searchtide, a continuous echo- 

 gram was made on a Gifft GDR-T depth re- 



corder' driving a hull-mounted UQN-1 trans- 

 ducer at 12 kHz. Shortly after cresting the 

 Coronado Escarpment, where the bottom 

 dropped off to the deeper water of the San Di- 

 ego Trough, hyperbolic targets appeared in the 

 160 to 270 m region of the recording. Under- 

 way at 12 knots, the largest of these had dimen- 

 sions of 600 m horizontally, and 70 m vertically. 

 As Searchtide hove-to at the dive site, these 

 targets appeared as in Figure 1. Interspersed 

 with the large targets were several discrete 

 targets which appear on the record as lines, 

 rather than large masses. The bottom depth at 

 the site was approximately 1,200 m and its trace 

 was programmed out of the recording. 



1103 



1125 



1205 



TIME (PST) 



Figure 1. — Echogram recorded during Deepstar dive 

 502. The large targets between 150 and 250 m were 

 observed to be schools of anchovy. The discrete traces 

 may have been blue sharks. During the underway por- 

 tion, the ship was repositioning over the submersible for 

 tracking purposes. The acoustic return from Deepstar, 

 a 2-m-diameter sphere, is labeled to provide a qualitative 

 comparison of acoustic reflection strength. 



The dive began at 1103 (PST), and a slow 

 descent (13 m/min) was made to 100 m where 

 two blue sharks were observed. This shark is 

 a common species which is easily identified vis- 



' Reference to trade names in this publication does not 

 imply endorsement of commercial products by the Na- 

 tional Marine Fisheries Service. 



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