SKIPJACK TUNA SPAWNING IN THE MARQUESAS ISLANDS AND TUAMOTU 



ARCHIPELAGO 



By Howard O. Yoshida, Fishery Biologist (General) 

 Bureau of Commercial Fisheries Biological Laboratory, Honolulu, Hawaii 



Spawning of skipjack tuna (Katsmvonus pelamis) in 

 the Marquesas and Tuamotu areas was investigated by 

 examining ova from 402 pairs of ovaries collected during 

 exploratory fishing cruises, August 1956 to June 1958. 

 Investigated were size at first spawning, spawning 

 season, frequency of spawning, fecundity, use of the 

 gonad index as a measure of maturity of skipjack, and 

 the relation of stage of sexual development to schooling 

 behavior. 



The length at first spawning of skipjack in the two 



ABSTRACT 



areas was found to be about 43 cm., although a few fish 

 as large as 50.7 cm. apparently were not yet ready to 

 spawn. Spawning activity reached a peak during 

 November-April. The data indicate a possibility that 

 individual skipjack may spawn more than once during 

 a season. Number of ova extruded per spawning was 

 estimated at 0.1 to 2 million. The gonad index could 

 not be used as a measure of sexual development. Skip- 

 jack schools tended to have fish in a similar stage of 

 sexual development. 



From 1956 to 1959 the staff of the Bureau of 

 Commercial Fisheries Biological Laboratory at 

 Honolulu investigated the tuna resources of waters 

 of French Oceania around the Marquesas Islands 

 and the Tuamotu Archipelago. A study of the 

 spawning of the skipjack tuna, Katsuwonus 

 pelamis (Linnaeus), which appears to be the most 

 abundant surface-schooling species of tuna in 

 this aren, was included in the investigations. 



This study is based on the systematic micro- 

 scopic examination and measurement of the ova 

 in skipjack ovaries, generally following the method 

 described by Clark (1934). Skipjack spawning 

 studies, based generally on the examination of 

 gonads or on the capture of larvae and juveniles, 

 have been made in many different areas of the 

 Pacific. On the basis of the examination of 

 gonads, Matsui (1942) inferred that skipjack 

 may spawn throughout the year in the vicinity 

 of Palau; Marr (194S) concluded that spawning 



Xute.— Approved for publication Oct. 22, 1964. 

 FISHERY BULLETIN: VOLUME 65, NO. 2 



occurs in the northern Marshall Islands, and 

 confirmed this by the capture of two juveniles; 

 Yabe (1954) and Yao (1955) found evidence of 

 spawning in the southern waters of Japan; Brock 

 (1954) postulated that they spawn in Hawaii from 

 late February, March, or April to the first part 

 of September; Schaefer and Orange (1956) and 

 Orange (1961) hypothesized that they spawn in 

 the vicinity of the Revilla Gigedo Islands in the 

 eastern Pacific; and Wade (1950a) found evidence 

 of their spawning in Philippine waters. 



By virtue of the capture of larvae and juveniles, 

 Schaefer and Marr (1948) demonstrated the 

 existence of a spawning ground off Central 

 America; Wade (1950b and 1951) found further 

 evidence that skipjack spawn in Phdippine waters; 

 Shimada (1951) deduced that spawning occurs 

 around the Phoenix Islands; and Matsumoto 

 (1958) showed that they spawn in a wide area in 

 the central Pacific Ocean. The present study 

 demonstrates the existence of yet another spawn- 

 ing locality in the Pacific. 



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