4.22 Changes in abundance 



Changes caused by hydrographic conditions are 

 referred to in general terms in 2.3. 



4.23 Average density 



Howard and Ueyanagi (1965) indicated catches of I. 

 platypterus by the number caught per tuna longline 

 operation (approximately 2,000 hooks) for a com- 

 posite year in the Pacific Ocean. In oceanic fishing 

 operations the catches are shown to be generally 1.1- 

 5.0 fish per operation while closer to land masses the 

 average density was approximately 5.1-10.00 fish per 

 operation in areas commonly fished by Japanese 

 longliners. 



For comparison, an average hook-rate of 0.168 

 sailfish per 100 hooks was obtained from 154 longlin- 

 ing operations in the equatorial western Indian Ocean 

 during 1964-67 (Merrett, 1971). This figure is similar 

 to that (0.14 for 100 hooks) obtained by Williams 

 (1967) during an earlier survey. 



4.24 Changes in density 



Kume and Joseph (1969a) showed that heavy long- 

 line fishing had affected the apparent abundance of 

 sailfish in the waters off Central America. The initial 

 hook-rate in 1964 was 10.6 per 100 hooks, 9.5 the 

 following year, and 5.8 in 1966. 



Williams (1970) examined the catches of a sport 

 fishery in the equatorial western Indian Ocean off the 

 Kenya coast from 1958-68 and his results are shown in 

 Figure 9. He indicated that, with effort relatively 

 stable, the catch and catch per unit effort (CUE) 

 paralleled one another over the 10-yr period. He 

 pointed out, however, that while the CUE and catches 

 have increased since 1962, there was a sharp decline in 

 the mean (and median) weight of fish caught. 



Kume and Joseph (1969a) indicated the seasonal 

 trends in density reflected by the catches of sailfish 



Figure 9.— Sailfish effort, catch, and catch per unit effort for 

 the 10 seasons from 1958 through 1968 at Malindi, Kenya (from 

 Williams, 1970). 



within 370-550 km of the coast in the tropical eastern 

 Pacific. They showed that in the northern hemisphere 

 the area of highest sailfish abundance is between 

 Guatemala and the mouth of the Gulf of California. In 

 the area around central Mexico sailfish appear abun- 

 dant all year; during the first quarter this is the only 

 area where they are. During the second quarter, there 

 appears to be a southerly extension of the area of high 

 abundance to as far south as lat. 10° N. This is main- 

 tained during the third quarter as well as a northward 

 movement of fish to about lat. 20°-22°N. By the 

 fourth quarter they reported a northward shift in the 

 southern limit to about 15°N and in the northern 

 limit to about lat. 25°N. 



Evidence of seasonal changes in density of sailfish 

 in the equatorial western Indian Ocean was given by 

 Williams (1967, 1970) and Merrett (1968a, 1971). In 

 the tuna longline survey off the East African coast 

 during 1958-60, Williams (1967) found a mean hook- 

 rate of 0.01 per 100 hooks during the southeast mon- 

 soon (April-October) while in the northeast monsoon 

 (November-March) it rose to 0.31 per 100 hooks. Con- 

 tinuing this survey (1964-67) in a wider area of the 

 equatorial western Indian Ocean, Merrett (1971) con- 

 firmed the earlier results by obtaining hook-rates of 

 0.11 per 100 hooks during the southeast monsoon and 

 0.35 per 100 hooks during the northeast monsoon. 

 Williams (1970) indicated more specifically the 

 seasonal variation in density off the Kenya coast. He 

 showed that, with few exceptions, sailfish are 

 restricted to the period October to March, with peak 

 catches coming in December and January. The 

 catches of the latter 2 mo constituted 47.6-77.3% of 

 the seasonal totals. 



4.3 Natality and Recruitment 



4.31 Reproduction rates 

 Nothing found in the literature. 



4.32 Factors affecting reproduction 

 Nothing found in the literature. 



4.33 Recruitment 



According to de Sylva (1957) some sailfish first 

 enter the catches of the sport fishery in the southern 

 Florida area during the winter at an age of about 6 mo. 

 Based upon de Sylva's age determinations, the age of 

 recruits to the East China Sea fishery reported upon 

 by Koto and Kodama (1962) is likely to be ap- 

 proximately 1 yr old (modal size: 140-175 cm). In the 

 sport fishery off Malindi, Kenya, Williams (1970) 

 found a modal size of 249-cm total length (29.5-31.3 

 kg), which is slightly longer at the same weight than 

 that of a 42-mo-old Atlantic fish. However, he pointed 

 out that this mode may be expected to include at least 

 two successive year classes and that a constant growth 



115 



