Fish Bulletin No. 82. A Comparison of the Populations of Yellowfin Tuna, Neothunnus macropterus, From the Eastern and Central Pacific
The present study is a continuation of the work published in 1948 by the senior author. At that time the attempt was made to determine whether or not the yellowfin tuna from Japan and from the Hawaiian Islands comprised populations distinct from and nonintermingling with that of the eastern Pacific region exploited by the California fleet. Using body measurements, empirical regression lines for those characters investigated were established for the eastern Pacific population, based upon 13 separate samples comprising a total of approximately 1,900 fish. It was found that, although these samples differed significally in a statistical sense from one another when tested by methods of analysis of variance, nevertheless all sample regression lines from these grounds conformed to the empirical population regression lines within narrow limits. When the data from the Japanese and Hawaiian samples were compared with the local population regression lines, it was found that in some characters these samples diverged from the local stock by amounts many times greater than the most divergent local sample. (Local, as used herein, refers to the eastern Pacific population.) The Japanese fish diverged more than the Hawaiian, but in all cases the direction of divergence was the same, suggesting a closer relationship between the Japanese and Hawaiian populations than existed between either of these with the local stock. The tentative conclusion was therefore drawn that the local, or eastern Pacific, stock of yellowfin tuna was separate and distinct from that of the central and western Pacific. While this conclusion represented the most probable hypothesis upon which to formulate a management program, it was nevertheless based upon a single small sample from each of the two distant regions. Every effort was therefore made to obtain additional and larger samples in order to check this important conclusion. In the summer of 1948 we succeeded in getting a sample of 58 yellowfin tuna caught in the vicinity of the Hawaiian Islands during the course of a cruise of the State's research vessel N. B. SCOFIELD. This sample was derived in part from Johnston Island (16° 31' N., 169° 25' W.) and in part from those banks and islands situated between French Frigate Shoals and the island of Kauai. It is therefore a composite sample from the region rather than from any one specific area. The fish in this sample were relatively small and the range in body length extended from 224 to 851 millimeters. Three of the smallest fish were eliminated from the final sample because lack of small calipers prevented us from making comparable measurements. The residual range in body length was from 514 to 851 millimeters. Because of this restricted size range, we attempted to supplement the sample by obtaining measurements from larger yellowfin delivered to the Honolulu markets at the time we were in port. Here we added 24 measurements to each series, made upon large, locally caught yellowfin, and thus extended the range to 1,638 millimeters. A few months later we were fortunate in obtaining comparable measurements upon 94 fish in a load of yellowfin tuna caught in the central Pacific in February, 1949, by the vessel CALISTAR. Again, this is a composite sample as the fish in the load were caught in part at Palmyra Island (5° 52' N., 162° 02' W.) and in part at Fanning Island (3° 50' N., 159° 20' W.). In April, 1950, before this analysis was completed, a small shipment of yellowfin tuna from the Fiji Islands was received by a local canner. of this shipment we obtained measurements upon 13 yellowfin, all caught in the vicinity of Suva. These three additional samples afforded the desired opportunity to check the tentative conclusions drawn from the analysis of the original samples; and in addition, the four available samples from the central pacific furnished material for a preliminary test of the homogeneity of the stock within that region.