SPAWNING OF YELLOWFIN TUNA 



63 



MAR APft MAY JUN JUL AUG SEP OCT NOV OcC 



Figure 11. — Comparison of monthly yellowfin tuna land- 

 ings for 1950 ( ) and the percentage of maturing 



females, as determined by the ovary weight-fish weight 

 regressions ( ). 



SUMMARY 



Ovaries from yellowfin tuna sampled from the 

 longline catches landed at Honolulu during 1950 

 •were used to determine the developmental changes 

 that take place in the gonads during the breeding 

 season, and data on the spawning of this species 

 in Hawaii are presented. 



It was found that several developmental groups 

 of ova are present in the ovaries of individual fish 

 during the breeding season. Based on diameter 

 measurements of the most mature ova present, 11 

 arbitrary stages of maturity were established 

 which trace the maturation of the ova from the 

 immature stage through the spawning stage. 



Several lines of evidence suggest that individual 

 fish mature more than one group of ova and have 

 several spawnings during the same season in 

 Hawaiian waters. The number of ova produced 

 in one spawning ranges from about 2,000,000 in 

 small females to about 8,000,000 in large females. 



Plotting ovary weight against fish weight 

 yielded linear relations whereby the spawning con- 

 dition of yellowfin tuna could be determined, thus 

 providing a simple guide for distinguishing 

 spawning from nonspawning fish without measur- 

 ing ova. 



The spawning period in Hawaiian waters dur- 

 ing 1950 extended from about the middle of May 

 to the end of October, and it was during this pe- 

 riod that the best catches of yellowfin tuna were 

 made in the longline fishery. 



LITERATURE CITED 



Clark, Frances N. 

 1925. The life history of Leuresthes tenuis, an ather- 

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 51pp. 

 1929. The life history of the California jack smelt, 

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 Game Comm., Fish Bull. No. 16. 23 pp. 

 1934. Maturity of the California sardine (Sardina 

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 California Div. Fish and Game, Fish Bull. No. 42. 

 49 pp. 

 (ioiisiL, H. C, and Robert D. Byers. 



1944. A systematic study of the Pacific tunas. Cali- 

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HATAI, SlIINKISnl, ET AX. 



1941. A symposium on the investigation of tuna and 

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 1950. [Trans, from South Sea Sci. (Kagaku Nanyo), 

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IIOEK, P. P. C. 



1895. Statistische und biologische untersuchungen an 

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KlSSELEVlTCH, K. A. 



1923. Materials on the biology of the Caspian herrings. 

 1. The fertility of the Wolga-Caspian herrings. 

 Astrachan Ichty. Lab. Kept., vol. 5, No. 1, pp. 15-55. 

 tin Russian. English resume, pp. 53-55.] 

 Mark, John C. 



1945. Observations on the spawning of oceanic skip- 

 jack (Katsuwoniis pelamis) and yellowfin tuna 

 {Ncothunnua macroptems) in the northern Marshall 

 Islands. U. S. Fish aDd Wildlife Service, Fish. Bull., 

 vol. 51, No. 44, pp. 201-206. 



Mastebman, A. T. 



1913a. Salmon and freshwater fisheries. 1. Report 

 on investigations upon the salmon with special refer- 

 ence to age-determination by study of scales. Fish. 

 Investigations, ser. 1, voL 1, pp. 3-111. Board Agri. 

 Fish. London. 

 1913b. Salmon and freshwater fisheries. 2. Report on 

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Olsen, Ynqve H., and Daniel Merriman. 



1946. Studies on the marine resources of southern 

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