100 



(8.4) 



(9.9) 



(9.5) 



(12.9) 



(7.3) 



(12.1) 



Figure &. --Proportions of skipjack greater than 60 and 70 cm. long, from the length- 

 frequency samples taken during various months by the Hawaiian fishery. Total catch in 

 millions of pounds accompanies each panel. The shaded portion shows the summer peak 

 fishing period. 



catches are correlated with relatively high pro- 

 portions of fish between 60 and 70 cm. The oc- 

 casional influx of large fish during the nonsum- 

 mer period consists of fish larger than 70 cm. 



Length -Frequency Distributions 

 of Eastern Pacific Samples 



Length-frequency distributions for various 

 regions in the northern-eastern Pacific fishery 

 area, compiled by quarter years, are available 

 in Broadhead and Barrett (1964). The most com- 

 plete set of these data is from the coastal area 

 of Baja California and the Revillagigedo area. 

 These quarterly length-frequencies have been 

 superimposed for each year in figure 7. 



Figure 7 shows that an increase in size is not 

 always evident from quarter to quarter: size may 

 decrease, remain stable, or increase from one 

 quarter to the next. A decrease in size during a 

 subsequent quarter-year can be interpreted as an 

 influx of smaller size fish replacing the larger 

 fish of the previous quarter or the removal of 

 the latter by emigration or mortality. Stability 

 in size could be interpreted as a lack of growth, 

 a balance of growth and removal of fish as they 

 become larger . or a constant replacement of one 

 group by another of equivalent size in any one 

 quarter. An increase in size between quarters 

 may be due to growth of the present inhabitants 

 of an area, to the influx of large fish, or the re- 

 placement of smaller size fish by larger size 

 fish. 



The data of figure 7 were examined to deter- 

 mine the nature of the predominant shift in size 

 between quarters. The between-quarter differ- 

 ences in size were classified either as an in- 

 crease, a stability, or a decrease in size. These 

 classifications, which, of course, are subjective, 

 are presented in table 1. They show that in- 

 creases occur less frequently than decreases or 

 stability. Many of the increases occur between 

 the third and fourth quarters. The Baja Califor- 

 nia samples have more increases. 



A pattern seems evident for the Baja California 

 samples in that the fewest increases in size occur 

 between the second and third quarters. .Also for 

 some sets of years, the fourth-quarter size dis- 

 tribution seems related to the first-quarter size 

 distribution of the next subsequent year. Fur- 

 thermore, the data tend to indicate that the sizes 

 are more similar within years, particularly for 

 the second, third, and fourth quarters, than be- 

 tween years. 



There are also differences in skipjack size 

 among the areas of the eastern Pacific. Broad- 

 head and Barrett (1964) show that small skipjack 

 (modal length < 50 cm.) are predominant in the 

 Baja California area, large fish (modal size 

 > 60 cm.) are most common in the Gulf of Cali- 

 fornia and the Mexican coast at least in the first 

 quarter of the year, and finally fish of interme- 

 diate size are found in the Revillagigedo area. 

 However, the size composition of the Revilla- 

 gigedo samples has shifted relative to the Baja 

 California samples. From 1958 to 1960 the sizes 



