115 110 



Figure 1. — Subareas selected for examination of striped 

 marlin catch rates. 



from data obtained through the courtesy of the Far 

 Seas Fisheries Research Laboratory. Size composi- 

 tion data from the same source were summarized by 

 quarters of the year for 1965 and 1967-70 for two 

 subareas (as shown in Figs. 6 and 7). Monthly ther- 

 mocline topography (Fig. 8) was obtained directly 

 from the atlas of Robinson and Bauer (1971). 



SEASONAL VARIATIONS IN CATCH 

 RATES 



Monthly variations in the catch rates for striped 

 marlin in waters off Baja California (subareas SW 

 and SE) and off southern Mexico (subarea M) are 

 shown for the years 1963-70 in Figures 2, 3, and 4. 



In subarea SW (Fig. 2), the catch rates are lowest 

 from January through April, begin increasing from 

 about May, reach a peak between July and October, 

 and then decrease after November. It is noted that 

 there are relatively small between-year differences 

 in catch rates in this subarea. 



In subarea SE (east of SW) the catch rates show a 

 marked between-year variation (Fig. 3). The wide 

 fluctuations appear to be especially noticeable in 

 March and April, e.g. the lowest monthly catch rate 

 in 1968 occurred in April, which was also the month 

 showing the highest catch rate for 1970. The 

 between-year variability was least during the July- 

 September period. 



In subarea M, off southern Mexico, catch rates 

 are generally low between January and March. They 



begin increasing in April and are highest between 

 May and July (Fig. 4). After August the catch rates 

 tend to become lower, although the year-to-year 

 fluctuation is considerable. 



SIZE COMPOSITION 



The average weight-frequency distribution, by 

 quarters of the year, was compiled for the two sub- 

 areas shown in Figure 6. In the waters off Baja 

 California (subarea S'), the modal weight of the 

 larger size group is observed at 3 1 to 35 kg during the 

 first quarter (I-Q), at 35 to 39 kg during the second 

 quarter (II-Q), and at 39 to 47 kg during the third 

 quarter (III-Q) (Fig. 7). The average modal weights 

 tend to increase from the first to the third quarters. 

 There is only one size group during the third and 

 fourth quarters. The modal weight during the fourth 

 quarter (I V-Q) is 27 to 31 kg and is smaller than that 

 of the third quarter. There are two size groups during 

 the first and second quarters, the modal weights 

 being 11 to 15 kg and 15 to 19 kg, respectively. 



Data for subarea M' are available only for the 

 second quarter. During the second quarter two size 

 groups are present — one with a mode at 27 to 31 kg 

 and the other at 43 to 47 kg. The modal group of the 

 smaller-size fish is the more dominant of the two 

 groups. 



7. 

 4.0 



23.0 



x: 

 u 



<u 

 (_> 



2.0 



Sub- 

 Area SW 



1.0 



JFMAMJJASOND 



Figure 2. — Monthly variations in catch rates of striped 

 marlin in subarea SW. 1963-70. 



303 



