4.24 Changes in density 



Ueyanagi et al. (1970) reported on the annual 

 changes in longline catch and fishing effort for the 

 Atlantic Ocean during 1958 through 1966. Until 1962, 

 in the early stages of exploitation, the landings of blue 

 marlin increased with the expansion of the fishery. 

 After 1962, however, the catch per unit of effort show- 

 ed a definite decrease. The relative abundance of blue 

 marlin in 1965 is about one-fourth the level of 1962. 

 The relative abundance of blue marlin began to 

 decrease in the Atlantic Ocean after the fishing effort 

 extended over virtually the entire distributional area 

 of the species and after the annual landings exceeded 

 about 80,000 fish. 



Based on longline fishing data presented by Merrett 

 (1971) for the western Indian Ocean, the relative 

 abundance of the blue marlin decreased during the 

 period covered by the study. The catch rate decreased 

 from 0.204 fish per hundred hooks in 1964 to 0.020 fish 

 in 1966. 



For the blue marlin sport fishery in the northern 

 Gulf of Mexico, Nakamura and Rivas (1972) used 

 "number-of-fish-raised-per-hour-of-trolling" as an in- 

 dex of relative abundance. Their study only covered 



the 1971 fishing season (May through October) and 

 the relative abundance, by weekly periods, varied 

 from 0.012 to 0.130 fish-per-hour-of-trolling without 

 any marked peaks. 



See 2.1 and 2.3 for additional information on 

 seasonal variation of stocks. 



4.3 Natality and Recruitment 



4.31 Reproduction rates 

 No information available. 



4.32 Factors affecting reproduction 

 No information available. 



4.33 Recruitment 

 No information available. 



4.4 Mortality and Morbidity 

 4.41 Mortality rates 



No information available. 



o 

 * 



i 

 o 



300 



280 



260 



240 



220 



200 



180 



160 



140 



120 



IOO 



80 



60 



40 



20 







n r 



FEMALES 



(N=I04) 



"i 1 1 1 1 r 



"i r 



J I I L 



_ 



J L 



J_ 



_ 



140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 



LENGTH (CM) 



Figure 2. — The length-weight relationship of female blue marlin in the western Atlantic Ocean. 



11 



