September 1966 



COMMERCIAL FISHERIES REVIEW 



11 



The sonar equLpment was subjected to de- 

 tailed acceptance tests under the supervision 

 of the Defense Research Laboratory of the 

 University of Texas. The overall perform- 

 ance at sea was evaluated. The equipment 

 did not meet specifications in several areas: 

 The source level of the high frequency pro- 

 jector was about 10 decibels (referenced to 1 

 microbar) below that specified; the transducer 

 assembly did not scan or tilt properly at 

 speeds greater than 4 knots; minor lobes on 

 the vertical beam of the high frequency hy- 

 drophone was 10.5 decibels higher than ex- 

 pected; antifouling treatment of transducers 

 appeared ineffectual. 



To familiarize personnel with opera- 

 tional procedures, four types of sonar op- 

 erations were carried out: (1) tracking of 

 tuna schools, (2) searching with ship under- 

 way, (3) searching with ship hove to, and (4) 

 patrolling of long-line sets. 



To maximize opportunities to track 

 schools, the vessel approached bird flocks 

 which were located visually. Sonar con- 

 tacts were made with 28 schools. They were 

 2 schools of estimated 20-25 pound skipjack, 

 2 schools of estimated 12-14 pound skipjack, 

 7 schools of estimated 5-8 pound skipjack, 4 

 schools of estimated 1-3 pound skipjack, 1 

 school of estimated 100 -pound yellowfin, and 

 12 schools of unidentified fish. The greatest 

 distance of positive sonar contact with a 

 school; was 650 meters (2,1 32 feet). Success- 

 ful tracking varied from momentary con- 

 tacts to tracking a school of large skipjack 

 for 56 minutes. The sonar operator was able 

 to stay with the school even though it sounded 

 twice during that period. Successful tracking 

 of the elusive skipjack will require great skill, 

 persistence, and a technique which will have 

 to be developed step by step. 



A total of 42 hours was devoted to search- 

 ing with the vessel underway at 3-4 knots-- 

 38 hours were in darkness. Highlight of the 

 searching was the discovery of a surface 

 school of 100-pound yellowfin and a school of 

 large skipjack approximately 50 meters (164 

 feet) below the surface which eventually sur- 

 faced. Identifications were visual. Returns 

 of various descriptions were received from 

 12 unidentified targets. 



Searching with the sonar while the vessel 

 was not underway was done only at night- -2 

 nights (18 hours) in open ocean and 2 nights 

 (16 hours) anchored in 35 meters (114.8 



feet) of water. On each occasion a night 

 light was submersed 8 meters or 26.2 feet 

 below the surface to attract organisms. 

 During the 34 hours at this activity, three 

 characteristic types of sonar returns were 

 observed. Only one type was seen on any 

 given night but it recurred many times 

 throughout the night. One type was asso- 

 ciated with akule ( Trachurops crumeno- 

 phthalmus ) 35 centimeters or 13.8 inches 

 long caught at the stern of the vessel. 



Long-line gear was set on 4 days. A total of 

 60 baskets was set on the first day and 40 bas- 

 kets on subsequent days. The total catch was 5 

 big-eyed tuna ( Thunnus obesus) , 15 yellowfin 

 tuna (T. albacares), 6 skipjack tuna ( Euthynnus 

 pelamis ), 6 wahoo, 11 shortnose spearfish 

 ( Tetrapturus augustirostris) , 5 striped mar lin 

 ( Makairaaudax ), 1 unidentified marlin, 4 com- 

 mon dolphin ( Coryphaena hippurus) , 5 Alep- 

 Lsaurus sp., 5 great blue shark (Prionace 

 glauca) ," and 1 whitetip shark (Pterolamiops 

 longimanus). 



Of 127 sonar returns observed while the 

 vessel patrolled the longline, 3 were sub- 

 sequently matched with fish on the longline. 

 These were a shortnose spearfish, a yellow- 

 fin tuna, and a wahoo. A total of 62 of the 

 sonar returns was observed on the first day, 

 and experience from subsequent days sug- 

 gested that many of them were echo returns 

 from the gear itself. Eleven of the targets 

 were moving; a strong target was swimming 

 at a depth of 220 meters (721.6 feet). 



Some general observations of the cruise 

 were: (1) the sonar was used to determine 

 the depth of the longline on one occasion. 

 Midway between the two buoys the longline 

 was 103 meters or 337.8 feet below the sur- 

 face. (2) The sonar was used to determine 

 the depth of a 1 -meter (3.28 feet) plankton 

 net during a tow. The depth of the net was 

 calculated from the wire angle and the 

 length of wire out was 195 meters (639.6 

 feet) at the deepest part of the tow. The 

 depth of the net determined by the sonar at 

 the same time was 140 meters or 459.2 

 feet; (3) The ocean bottom was detected up to 

 1,600 meters, or 5,248 feet, the maximum 

 range of the sonar. 



Routine bathythermograph (BT) and weather 

 observations were made during the cruise 

 and all Alepisaurus sp. caught on the long- 

 line gear were preserved in formalin. 



