COMPARISON OF YELLOWFIN TUNA OF HAWAIIAN WATERS AND OF 



THE AMERICAN WEST COAST 



By MiLNER B. SCHAEFER, Fishery Research Biologist 



The yellowfin tuna of the vicinity of the Hawai- 

 ian Ishiuds, like the form from the adjacent waters 

 of the American west coast (Schaefer 1948), is 

 here referred to Neothunnus macropterus (Tem- 

 niinck and Schlegel) 1842. As has been pointed 

 out pre\nous]y (Schaefer and Walford 1950), it is 

 possible that the various Pacific forms, the form 

 from the Indian Ocean, and perhaps also those 

 from the Atlantic, should be considered a single 

 species of world-wide distribution. The data 

 presented herein support such a conclusion. 

 This cannot be finally settled until populations 

 from more places have been carefully studied, 

 particularly a series from the Indian Ocean from 

 which was described the specimen of A^. argen- 

 tiinttatus (Cuvier and Valenciennes) 1831, which 

 should be considered the type of this species. 

 It is also my opinion that the species now re- 

 ferred to the genera Thunnus, Neothunnus, Para- 

 thunnus, and Kishinoella should all be referred, 

 as has been done by Fraser-Brunner (1950), to a 

 single genus, Thunnus. However, since this 

 paper is written to compare the yellowfin tima 

 from the vicinity of the Hawaiian Islands with the 

 form from the waters adjacent to the American 

 west coast in order to settle the question whether 

 they are racially distinct, questions of taxonomy, 

 sjmonymy, and nomenclatm-e will be passed over 

 at this time, and for convenience both forms will 

 be referred to the commonly accepted name 

 A'', macropterus. 



The yello^vfin tuna is the object of an extensive 

 and intensive fishery along the American west 

 coast from California to the Galapagos Islands. 

 In the Hawaiian Islands there exists a minor 

 fishery that promises to be expanded in the near 

 futm-e to encompass other islands of the mid- 

 Pacific and to increase in intensity in the presently 

 exploited region. Wliether the population of the 

 Hawaiian region is part of the same stock of 

 fish as that fished along the American west coast, 

 or is an independent stock, is a question of con- 



siderable practical importance: if they are the 

 same stock, the new fisheries would merely add 

 to the strain on the stock already being exploited ; 

 if they are independent, there is being tapped an 

 essentially virgin resom-ce. 



Schaefer (1948) has pubhshed measurement 

 data and counts of denumerable characters on 

 yellowfin tuna from the waters of the Pacific 

 near Costa Rica. Godsil (1948) has published 

 the measui-ements of a few selected dunensions 

 taken from a very large number of specimens 

 from several sampling localities, extending from 

 the tip of lower California to Panama. Godsil 

 and Bj'ers (1944) have also published gdl-raker 

 coimts of value to the present study. Those 

 data and those presented herein from the Hawai- 

 ian Islands are dii'ectly comparable, having been 

 taken in the same manner. Details of measure- 

 ment methods are given in the papers cited and 

 by Marr and Schaefer (1949). Measm-ements 

 were made by several field assistants, but all 

 followed identical procedures. 



For tliis study, Hawaiian yellowfin tuna were 

 measm-ed during 1949, between February 21 and 

 September 28. They were selected to give as 

 even a representation as practicable of all sizes 

 of fish available. All specimens were fresh and 

 recently landed from commercial fishing vessels. 

 Most specimens were measm-ed at the Honolulu 

 fresh-fish wholesale auction market, not only a 

 very convenient place to work but almost ideal 

 from a sampling standpoint. 



The fish handled there are caught by flag- 

 lines which, by the nature of their operation, 

 sample the fish population very widely. De- 

 scription of the fishery and the method of handling 

 and marketing the fish ^vill be foimd in June 

 (1950). Smaller sizes of yellowfin tuna, under 

 about 80 cm. in total length, are seldom taken 

 by the flag-line fishery. These small fish are 

 frequently taken by pole-and-line fishmg, in the 

 same manner as on the American west coast, 



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