which had swallowed a bigeye tuna weighing about 50 

 kg (about 110 lb). 



The blue marlin is known to feed at and near the 

 surface, but there are indications that it may also feed 

 in relatively deep water. Off Puerto Rico, deep-sea 

 fishes, such as Pseudoscopelus, were found in blue 

 marlin stomachs (Erdman, 1962). The deep-dwelling 

 squirrelfish, Holocentrus lacteoguttatus, was found in 

 Hawaiian blue marlin stomachs by Strasburg (1970). 



3.43 Growth rate 



There is very little information on growth rate 

 although estimates could be obtained from analyses of 

 modal progressions in length and weight frequencies. 

 Royce (1957) presented data on weight frequency for 

 central Pacific blue marlin but no modal progression 

 can be ascertained. Kume and Joseph (1969b) 

 presented and discussed data on the size composition 

 of blue marlin in the eastern Pacific, but they could 

 not estimate growth from progression of modal 

 groups. 



3.44 Metabolism 

 No information available. 



3.5 Behavior 



Feeding behavior is discussed above under 3.41. 

 There is no information on reproductive behavior. 



3.51 Migrations and local movements 



Ovchinnikov (1970) mentioned that, in the western 

 Atlantic, distribution by months indicate that the 

 blue marlin shows a tendency to seasonal migrations. 

 Mather et al. (1972) are of the opinion that longline 

 catches have produced no evidence that the blue 

 marlin moves between the northwestern and 

 southwestern Atlantic. These authors believe that 

 there may be two populations in the western Atlantic 

 or that there may be a single population which is un- 

 available to the fishery while the fish are migrating 

 between the areas. 



In the northwestern Atlantic, 561 blue marlin have 

 been tagged since 1955 and only 4 have been recap- 

 tured, all near their respective release points (Mather, 

 1971). Although these tag returns are inconclusive, it 

 does indicate that meaningful information can be ob- 

 tained if sufficient numbers of fish are tagged. 



For the central Pacific, Royce (1957) stated that 

 north of the equatorial area the seasonal occurrence of 

 blue marlin suggests a northward summer movement 

 followed by a return south in late autumn. Anraku 

 and Yabuta (1959) considered blue marlin in the 

 Pacific to be a single intermingling unit which moves 

 to the southeastern Pacific during the southern 

 summer and returns to the northwestern Pacific dur- 

 ing the northern summer. In the southeastern Pacific, 



Suda and Schaefer (1965) postulated a "strong active 

 migration" of blue marlin in the vicinity of lat. 20°S 

 long. 120°W. Howard and Ueyanagi (1965) indicated 

 that the blue marlin migrates between the North and 

 South Pacific towards the southeast and northwest, 

 respectively. Fish taking part in this seasonal migra- 

 tion are generally limited in size, 140 to 180 cm; a few 

 larger fish over 200 cm also take part in the migration. 

 This suggests differential migration by sex, migration 

 activity being greater in males. Howard and Ueyanagi 

 consider that migration between the North and South 

 Pacific indicates shift of habitat in accordance with 

 spawning and seasonal change of sea conditions. 



In the Pacific Ocean, 170 blue marlin have been 

 tagged from 1963 through 1970. There have been no 

 recoveries to date. 



Sonic tags have already proved useful in studies of 

 migration and local movements. A blue marlin was 

 tagged on 14 July in Hawaii 3.1 miles west of Keauhou 

 (Yuen, Dizon, and Uchiyama, 1974). The tag was in- 

 serted at 0935 and the fish was tracked by the NMFS 

 RV Charles H. Gilbert until 0800 the next morning. A 

 temperature sensitive sonic tag was selected in order 

 to also obtain information on the depth of the fish. 

 During the tracking period, the fish moved to about 25 

 miles north of the point of release on an erratic course 

 between the 183- and 549-m (100- and 300-fathom) 

 isobaths. Calculated speeds of the fish ranged from 

 0.6 to 4.4 knots with an average of 1.6. Swimming 

 depth varied from the surface to about 73 m (40 

 fathoms) but it was mostly in the upper 37 m (about 

 20 fathoms). 



3.52 Schooling 



According to published information, mostly in the 

 sport fishing literature, the blue marlin has never 

 been observed occurring in schools. Verbal reports 

 from anglers and sport fishing guides and my own 

 observations confirm this. Occasionally, two or three 

 fish will rise simultaneously to baits trolled from a 

 single boat which indicates a small aggregation but 

 not what would be termed a school. Ovchinnikov 

 (1970) states that, unlike the sailfish, the blue marlin 

 does not form "accumulations" in coastal waters. He 

 also reports that, in the open ocean, blue marlin rarely 

 gather in schools but are usually found "scattered 

 singly." 



Data on composition of blue marlin stocks by size 

 and sex are given by various workers for the Atlantic 

 and the Indo-Pacific. 



Royce (1957) recorded weight frequencies by month 

 for 4,712 central Pacific blue marlin but the sex was 

 not recorded. According to Strasburg (1970), Royce's 

 data show that the weight distribution was wide in 

 January when 45- to 136-kg (100- to 300-lb) fish 

 dominated the catch. By April, heavier fish 136 to 227 

 kg (300 to 500 lb), presumably females, were more 

 common. By June, smaller fish, presumably males, 



