CATCH RATE, SIZE, SEX, AND FOOD OF TUNAS AND OTHER PELAGIC FISHES 

 TAKEN BY TROLLING OFF OAHU, HAWAII, 1951-55 



By 



Albert L. Tester 



and 



Eugene L, Nakamura 



Fishery Research Biologists 



Pacific Oceanic Fishery Investigations 



Honolulu, Hawaii 



During 1951 to 1955 inclusive, the 46-foot 

 research vessel S a 1 p a (frontispiece) of the 

 Hawaii Marine Laboratory, University of Hawaii, 

 conducted trolling operations off Kaneohe Bay on 

 the windward or northeast side of Oahu. Fishing 

 was undertaken primarily to stock the ponds of 

 the Coconut Island laboratory with tunas and 

 other pelagic fishes for studies of their response 

 to stimuli. The studies were supported by three 

 annual contracts (June 1951 to May 1954) between 

 the University of Hawaii and the Pacific Oceanic 

 Fishery Investigations. 



Incidental to the fishing operations, data 

 were accumulated on the catch rate, size, sex, 

 and food of the several species which were 

 caught. The data are summarized in this report 

 primarily to make them available to other re- 

 search workers studying the biology of these 

 pelagic species. Such inferences as may be 

 made concerning the life histories of the fish 

 are presented briefly and should be considered 

 tentative in view of the paucity of data in many 

 instances. 



The species discussed in this report are 

 referred to by their common English names as 

 follows: 



Scientific name 



Katsuwonus pelamis 

 Euthynnus yaito 

 Neothunnus macropterus 

 Auxis thazard 

 Coryphaena hippur us 

 Car anx stellatus ? 

 Acanthocybium solandri 



English name 



Skipjack 



Little tunny 



Yellowfin 



Frigate mackerel 



Dolphin 



Jack 



W ahoo 



and 1952, ordinarily six cotton trolling lines 

 were used, two (about 90 feet in length) from 

 each of two outrigger poles, and one (about 30 

 feet) from each side of the stern. During 1953 

 to 1955, the four outrigger lines were used, but 

 for the most part only one line was trolled from 

 the stern and, on infrequent occasions, even 

 this was omitted. Since the catch rate is calcu- 

 lated as the average catch per hour rather than 

 per line per hour—' this introduces a bias in 

 year to year comparisons, but this is considered 

 insufficient to account wholly for the changes in 

 catch rate to be noted later. 



Stainless-steel leader wires (about 6 feet 

 in length) were snapped to the ends of the cotton 

 lines. To these were attached a variety of 

 lures. Trolling was conducted at a speed of 

 about 6 knots, which kept the lures on or near 

 the surface. After capture, viable fish were 

 retained in the ship's livewell. 



Fishing was confined mostly to the morning 

 hours, with the ship leaving the dock at the 

 Coconut Island laboratory between 0700 and 0800 

 hour s and returning between 1200 and 1300 hours. 

 On clearing Kaneohe Bay we would usually bear 

 towards Mokumanu Island (fig. 1) and then head 

 out to sea, the course being governed by such 

 bird flocks as were sighted within the area of 

 fishing. Often the ship would circle under a 

 working bird flock for several minutes. When- 

 ever strikes were made, trolling would be con- 

 tinued in the vicinity until there was reasonable 

 assurance that no further catches could be made. 

 Occasionally trolling would be terminated, even 

 though more fish could have been caught in the 

 vicinity, in order to avoid delay in transporting 

 viable fish to the ponds at Coconut Island. The 

 general fishing area, shown in figure 1, was 



METHODS 



Fishing methods used in 1951 have been 

 described by Tester (1952) and, in general, did 

 not change in subsequent years. During 1951 



— Accurate data on number of lines used 

 per trip are not available in some years. 



