in the western and central North Pacific, between lat. 

 2° and 24°N. In April and November the fish tend to 

 concentrate in the equatorial Pacific between lat. 

 10°N and 10°S. As in the Atlantic, the blue marlin in 

 the Pacific Ocean is less abundant towards the East. 

 In the extreme eastern Pacific, off the continental 

 coast, the fish usually occurs between lat. 23°N and 

 3°S. Kume and Joseph (1969b) indicate that blue 

 marlin occur in heaviest concentrations at about lat. 

 20°S and west of long. 110°W, north of lat. 13°N; 

 however, their relative abundance is quite low. Kume 

 and Joseph (1969a) record longline catches along the 

 Peruvian coast as far south as lat. 12°S. 



In the Indian Ocean, the blue marlin is known to oc- 

 cur around Ceylon, Mauritius, and off the east coast 

 of Africa (Morrow, 1959a, 1964). Off the east coast of 

 Africa, between the equator and lat. 13°S, the blue 

 marlin is apparently abundant during the southeast 

 monsoon period, April to October (Merrett, 1971). 



2.2 Differential Distribution 



2.21 Spawn, larvae, and juveniles 



Areas of occurrence and seasonal variations: Three 

 larvae were reported by Gehringer (1956) from the 

 western Atlantic off Georgia (lat. 30°57'N, long. 

 79°37'W). These were later identified as blue marlin 

 larvae by Ueyanagi and Yabe (1959). Two postlarvae 

 were recorded from Jamaica by Caldwell (1962). 

 Eschmeyer and Bullis (1968) recorded four larvae and 

 postlarvae from the western Atlantic (two off Cat Cay, 

 Bahamas, one at lat. 32°06'N, long. 72°00'W and one 

 at about 40 miles northest of Fort Pierce, Fla.). 

 Bartlett and Haedrich (1968) recorded 85 larvae from 

 off Brazil between Cabo de Sao Roque and lat. 26°S. 

 Ueyanagi and Yabe (1959) recorded about 400 lar- 

 vae from the western Pacific, and Ueyanagi (1964) 

 reported that 1,015 larvae had been collected in the 

 Pacific. Ueyanagi et al. (1970) have given the seasonal 

 distribution of larval blue marlin for the Atlantic. 



2.22 Adults 



Areas of occurrence and seasonal variations: In most 

 areas within its range the occurrence of adult male 

 marlin appears to be seasonal and in some regions 

 there is also a seasonal variation by sex. 



The seasonal variation and relative abundance of 

 blue marlin in the northern Gulf of Mexico have been 

 discussed by Nakamura and Rivas (1972). Off Puerto 

 Rico the largest numbers of blue marlin have been 

 caught during August, September, and October, and 

 the smallest catches have been made in December 

 (Erdman, 1962). In Hawaii, blue marlin catches are 

 also highest in summer and lowest in winter (Royce, 

 1957; Strasburg, 1970). 



Very large blue marlin, probably females, are 

 reported to occur off the south coast of Jamaica in the 

 summer while similar large fish are reported off the 



north coast in the winter (de Sylva, 1963). Nine blue 

 marlin specimens taken in late December and early 

 January from Jamaican waters were examined by me; 

 all were males. Off Puerto Rico, males and females oc- 

 cur in about equal numbers in July and August; larger 

 males tend to appear in May and there is a sudden in- 

 crease of small males in September (Erdman, 1968). 

 In the eastern Pacific, extreme differences in sex 

 ratios between certain regions suggest strongly the 

 possibility that blue marlin segregate into distinct 

 areal groups according to sex (Kume and Joseph, 

 1969b). 



2.3 Determinants of Distribution Changes 



Effects of ecological determinants: The distribution 

 of the blue marlin is mostly confined to the tropics 

 within the 24°C surface isotherms of both 

 hemispheres, and is noted to shift northward and 

 southward according to season. In the western Atlan- 

 tic off the northeastern United States, blue marlin 

 have been taken in waters with surface temperatures 

 ranging from 23.9° to 28.3°C (Squire, 1962). Blue 

 marlin catches were recorded at 47 longline stations 

 occupied during the past 22 yr by National Marine 

 Fisheries Service (NMFS) vessels in the Caribbean 

 Sea, Gulf of Mexico, and off the southeastern United 

 States; surface temperatures at these stations ranged 

 from 21.7° (February) to 30.5°C (July). 



In certain regions water masses and currents ap- 

 parently affect the horizontal and seasonal distribu- 

 tion of the blue marlin. For example, in the northern 

 Gulf of Mexico the occurrence of blue marlin seems to 

 be controlled by the so-called "Loop Current." This 

 current, an extension of the Caribbean Current, flows 

 northward into the Gulf through the Yucatan 

 Channel. Its northward extent is seasonal and reaches 

 its maximum in the summer. 



Water color also affects the occurrence of the blue 

 marlin, at least in the northern Gulf of Mexico, where 

 the fish shows preference for blue water (Nakamura 

 and Rivas, 1972). 



There is indication of a periodic fluctuation in 

 abundance which is probably due to ecological in- 

 teraction with other species of marlin. For example, 

 within the fishing season (April to November) in the 

 northern Gulf of Mexico, anglers tend to catch more 

 blue marlin when the white marlin catch is lowest and 

 vice versa (Nakamura and Rivas, 1972). A similar 

 phenomenon was reported by Strasburg ( 1970) for the 

 blue and striped marlins around Hawaii. Strasburg 

 suggests that perhaps each responds to some en- 

 vironmental factor, such as temperature or food, in a 

 way which excludes the other. 



2.4 Hybridization 



There are no records of hybridization for the blue 

 marlin. 



