stability or decreases in size 



Table 1. --Between quarter Increases in size (+) and ^^-^^^j.^^ „^ „^^i 



(-) for major portion of skipjack length distributions sampled from fish taken in 

 the Baja California and Revillagigedo region of the eastern Pacific. Blank spaces 

 indicate no data. These changes in size are interpreted from data presented by 

 Broadhead and Barrett (1964) 



the eastern Pacific and Hawaiian fisheries for 

 only 3 years (1954, 1959, 1960) have been pub- 

 lished. As previously noted the most complete 

 set of data from the eastern Pacific is from Baja 

 California and Revillagigedo samples. Since the 

 fairly consistent relationship of sizes between 

 areas of the northern-eastern Pacific already 

 has been indicated, it will suffice to compare the 

 Baja California size distribution with that of the 

 Hawaiian fishery. To place the material on a 

 com par able basis with that of the eastern Pacific, 

 the Hawaiian data have been compiled by quarter- 

 years and plotted on an increased scale (fig. 8). 

 These composite curves are, of course, weighted 

 by the number of fish in each size for each month 

 or subregion included in the sample. The large 



600 700 



LENGTH (MM ) 



Figure 8. --Length- frequency distributions of 

 skipjack taken during the third quarter of 

 the year from fisheries off Baja California 

 and the Hawaiian Islands. Note that the 

 Hawaiian length- frequencies are plotted on 

 an increased scale. Data on Baja California 

 samples are taken from Broadhead and Barrett 

 (1964). 



number of samples and measurements suggests 

 that the curves are fairly representative of 

 lengths in the population for the considered time 

 period and that they have an accuracy suitable 

 to illustrate the points to be discussed. 



In general the curves for the Hawaiian samples 

 arebimodal; those for the Baja California sam- 

 ples for the most part have a single mode. The 

 connotations of unimodal and bimodal, in this 

 case, refer to the general appearance of the 

 curves and are not intended to exclude the possi- 

 bility of more than one modal group within a 

 particular mode. 



Discrepancies in the length-frequency distri- 

 butions, during the various quarters, between 

 Hawaiian and Baja California samples may be 

 attributed to a variety of causes. Some of these 

 causes are probably related to differences in the 

 time sequence--between Hawaii and the eastern 

 Pacific--of the previously mentioned phenomena 

 which affect stability in size (i.e. , balances among 

 growth, immigration, and emigration). Of par- 

 ticular interest are the third quarter length- 

 frequencies because these generally reflect peak 

 catches in the Hawaiian and eastern Pacific. It 

 is likely that they, more than the samples at 

 other times of the year, most accurately repre- 

 sent the total population. 



The data for 1960 and 1954 show remarkable 

 similarities between the eastern Pacific and the 

 small-size Hawaiian fish. The minimum sizes 

 of fish from both fisheries are about the same, 

 and their distributions appear to have several 

 parallelisms in frequency. The 1959 distribu- 

 tions are, however, quite different. It would 

 seem, at least in some years, that the Hawaiian 

 and Baja California-Revillagigedo fish have com- 

 mon elements in size-frequency distribution. 



Movements 



This section considers skipjack movements as 

 inferred from tagging studies conducted by the 

 lATTC. These studies have yielded many short 

 distance recoveries and a total, to date, of three 

 midocean recoveries. 



