20 



COMMERCIAL FISHERIES REVIEW 



Vol. 28, No. 7 



The laboratory scientist says, "We have 

 found that two environmental indicators can 

 be related to better than average fishing. The 

 first is when the change of winter cooling of 

 the surface water to spring warming occurs 

 in February rather than in March. The sec- 

 ond is when waters bathing the islands during 

 the fishing season have a salinity of less than 

 34.8 parts per thousand. The first index, 

 since it occurs in February or March, is of 

 predictive value with respect to the main 

 skipjack season during the summer months. 

 This year the initial warming of the water 

 took place in March and therefore indicates 

 a fishing season with below average availabil- 

 ity of skipjack tuna." The fact that the water 

 warmed late, he points out, does not neces- 

 sarily preclude favorable low salinity water 

 from entering the islands region during the 

 spring. However, he says, "As of March 31, 

 Koko Head salinities have not yet begun their 

 seasonal decline. In the 10 years since 1956, 

 this has occurred only twice. That was in 

 1957 and 1960, when salinities began their 

 decline in early April, The 1957 and 1960 

 skipjack seasons were both below average. 

 Both 1957 and 1960 followed years with well 

 above average catches. The forecast for 

 1966 therefore is for below average landings, 

 as in 1960." 



The scientist points out that the physical 

 mechanisms which bring "favorable" water 

 to the islands are unknown and until they are 

 determined, the skipjack forecasts can be of 

 only general value. 



According to John C. Marr, the Bureau's 

 director of the Hawaii Area, whenever the 

 fishery differs substantially from the predic- 

 tion, more is learned about skipjack. In 196 5, 

 for example, the fishery was much better 

 than was expected on the basis of the Koko 

 Head data. It turned out that during 1965 the 

 catch of skipjack per unit of bait used was 

 much greater than had been the case for any 

 previous year. 



Note: See Commercial Fisheries Review , Jidy 1965 p. 19. 



5[c :^c :^ 5j: >|c 



TUNA BIOLOGICAL STUDIES CONTINUED: 



M/V " Charles H. Gilbert " Cruise 90 

 (March 31 -April 6, 1966): The return of live 

 yellowfin, skipjack, wavyback skipjack, and 

 frigate mackerel to Kewalo Basin for density 

 and red muscle size determination for loco- ■ 

 motion and hydrodynamic studies was one of 

 the main objectives of this cruise by the re- 



search vessel Charles H. Gilbert , of the U.S. 

 Bureau of Commercial Fisheries Biological 

 Laboratory at Honolulu, Hawaii. The area of 

 operations was within 100 miles of Oahu and 

 Kauai. 



Research vessel Charles H. Gilbert of the U.S. Bureau of Com- 

 mercial Fisheries. 



Other objectives of the cruise were to: 

 (1) collect and return live scombrids to be- 

 havior tank facilities for sensory threshold 

 and behavior experiments; (2) return yellow - 

 fin that have been chilled in ice for a packing 

 company to determine if blood streaks in 

 cooked fish can be avoided; (3) collect blood 

 samples for subpopulation analysis (Subpopu- 

 lations Program) of skipjack in the Hawaiian 

 Islands; (4) collect fresh samples of fish eye 

 lenses and brains for enzyme studies; and 

 (5) acquaint sea scouts with data collection 

 at sea and seamanship. 



Densities from 2 yellowfin and 1 skipjack 

 that were returned live to Kewalo Basin were 

 determined but scombrids of desired species 

 and size were not caught for red muscle size 

 determination. A total of 8 wavyback skipjack 

 was returned live to behavior tank facilities, 

 10 yellowfin were returned to the packing 

 company, 5 of which were chilled in ice and 

 5 were bled and chilled, 75 skipjack blood 

 samples were collected and chilled, and eye 

 lenses and brains of 2 dolphin and 5 wavyback 

 skipjack were collected. 



Thermograph and barograph were oper- 

 ated continuously during the cruise and the 

 usual standard watch for fish, birds, and 

 aquatic mammals was maintained. 



Trolling lines were out continuously be- 

 tween Kewalo Basin and each fishing station; 

 total trolling time was 40 hours 50 minutes. 

 Two skipjack ( Katsuwonus pelamis ), 11 wavy- 

 back skipjack ( Euthynnus affinis) , 18 yellow- 

 fin ( Thunnus albacares) , 3 dolphin ( Coryphaena 

 hippurus ) and 1 wahoo (Acanthocybium solan- 



