mercial Fisheries Biological Laboratory, Honolulu. 

 On a cruise in January and February 1968 off Kona 

 and off Johnston Island, 65 fish were caught, tagged, 

 and released; 44 were striped marlin, 10 were short- 

 bill spearfish, 7 were yellowfin tuna, and 1 each were 

 blue marlin, albacore, bigeye tuna, and wahoo. The 

 fish were tagged with a tubular yellow plastic tag that 

 was inserted in the back of the fish just below the 

 dorsal fin. The tags were serially numbered and 

 bore the name and return address of the Laboratory. 

 It is hoped that fishermen who land the tagged fish 

 will return the tag to the Laboratory, along with 

 information on the date, location, and size of the fish. 



Other scientists have deduced the nature of billfish 

 migrations by less direct means. Striped marlin 

 show a general poleward migration in warm weather, 

 followed by movement toward the Equator in winter. 

 Although the northern and southern populations of 

 Pacific striped marlin are thought to be discrete, 

 there may be an influx of small southeast Pacific fish 

 into the Hawaiian fishery in the summer. It is also 

 possible that the striped marlin that appear in south- 

 ern California in the summer come from the south. 



William F. Royce in 1957 summarized the avail- 

 able information on blue marlin movements with the 

 statement, "Thus, north of the equatorial area the 

 seasonal occurrence suggests a summer movement 

 northward followed by a return south in the late 

 autumn."- 7 A similar conclusion was drawn by 

 other authors, who also suggested a differential mi- 

 gration by sex in which males have greater migra- 

 tional activity than females. They suggested further 

 that the migrations may be related to sea conditions 

 and to spawning. 



Estimating Billfish Weight 



Graphs have been constructed that allow one to 

 estimate a fish's weight simply by measuring its 

 length. Three are included in this report (figs. 5, 6, 

 7). To estimate the weight of a blue marlin of 175 



2/ 



— Royce, William F. 1967. Observations on the 



spearfishes of the central Pacific. U.S. Fish Wildl. 



Serv., Fish. Bull. 57: 497-554. 



