marlin ventured beyond a bottom depth of 2,000 m 

 (Fig. 3). This marlin appeared to be returning to 

 shallower water when contact with it was lost. 



Swimming Depths 



The choices of swimming depths were quite dif- 

 ferent among the three marlin tracked. The largest 

 marlin (# I ). estimated at 270 kg (600 lb), spent half of 

 the time within 10 m of the surface, a sixth of the time 

 between 10 and 30 m, and the remaining third of the 

 time deeper than 30 m. The maximum swimming 

 depth, which was 80 m, was reached only on one 

 occasion. The next largest marlin tracked (about 135 

 kg or 300 lb) remained at depths between II 5 and 185 

 m throughout the SVi h that it was tracked. The last 

 and smallest blue marlin tracked (about 70 kg or 150 

 lb) remained in a depth zone of 60-85 m before it went 

 to the bottom after 2 h. 



The vertical movements of the largest marlin did 

 not show any pattern that could be related to time of 

 day. The other marlin were not tracked long enough 

 to determine if any pattern existed. 



Swimming Speeds 



Swimming speeds of the three marlin were calcu- 

 lated based on the distance traveled every half hour. 

 Results are in Table 2. The average swimming speed 

 of the last marlin is high compared with the others 

 especially in terms of body lengths per second. Mar- 

 lin #1 and #3 had an average swimming speed of 

 0.23 body length/sec. Marlin #5, in contrast, aver- 

 aged 0.45 body length/sec. The higher speed of the 

 last marlin may be a reflection of the distress of a 

 dying marlin. 



The maximum for the largest ( # I ) and the smallest 

 fish (#5) were 0.62 and 0.68 body length/sec com- 

 pared with 0.32 body length/sec for marlin #3. The 

 two larger marlin (#1 and #3) both had minimum 

 speeds of 0.09 body length/sec while the minimum 

 speed of the smallest was 0.19 body lengthysec. 



DISCUSSION 



A counterclockwise eddy west of the northern half 

 of the island of Hawaii persists there most of the time 

 ( R. A. Barkley , pers. comm.). The area of our marlin 

 tracking coincides with that part of the eddy which 

 flows northward. The fact that all three marlin 

 tracked exhibited a northerly movement suggests 

 the possibility that the blue marlin orients or drifts 

 with currents. 



One of the problems in tracking marlin is getting 

 one that will survive the trauma of being caught. Of 

 the five marlin tagged two died and one probably 

 died. Three others were caught and not tagged be- 

 cause of their poor condition. To enhance the prob- 

 abilities of success in marlin tracking, consideration 

 should be given to ways of attaching the tag without 

 catching the fish. 



ACKNOWLEDGMENT 



We wish to acknowledge the generosity and coop- 

 eration of anglers Alex Smith and Darrell Turner 

 and skipper Monty Brown and Wes Vannatta for 

 donating their catch for tagging. Special thanks go to 

 Bart Miller and his mate. Murray Mathews, of the 

 boat Christel for their enthusiasm and patience. We 

 also wish to thank Jack Benson and the students of 

 his Marine Technology training course of Leeward 

 Community College. 



Table 2. — Swimming speeds of blue marlin. 



268 



