Working Group Report on Identification of Larvae and Juveniles 



W. M. Matsumoto - Chairman 



S . Ueyanagi 



W. Klawe 



M. Watson (Mrs.) 



H. Nakamura, Observer 



W. G. Van Campen, Interpreter 



Reference: Papers No. 



VII - 6. Yabe, H. , and S. Ueyanagi - Contributions to the study of the early life history 

 of the tunas 



9. Matsumoto, W. M. - Identification of larvae of four species of tuna from the 

 Indo -Pacific region. I. 



13. Watson, M. E. , and F. J. Mather, III -Species identification of juvenile tunas 

 (genus Thunnus) from the Straits of Messina, Northwestern Atlantic, and the 

 Gulf of Mexico 



Perhaps the phase of tuna life history 

 about which we have the least information is the 

 period beginning with spawning and ending prior 

 to the time the young enter the fishery . In order 

 to fill this gap, studies of tuna eggs, larvae, and 

 juveniles are undertaken. A prerequisite of these 

 studies is the positive identification of species at 

 the various stages of development. The purpose 

 of the Working Group meeting, therefore, was 

 to discuss the validity of species identification 

 of larval and juvenile tunas as presented in the 

 several papers, to point out differences of opin- 

 ion, and to make recommendations regarding 

 these differences. It was also the intention of 

 the committee to delve into the methods and gear 

 for collecting tuna in the early stages of growth. 



Identification of Larvae 



It was pointed out that the two papers on 

 larval tuna identification were not in agreement 

 concerning two species, albacore and bigeye. 

 Of the species which were described in both pa- 

 pers, general agreement was found for one spe- 

 cies, T. orientalis . Concerning the point of 

 difference, the authors of the first paper felt that 

 two types of larvae (A and B) could be distin- 

 guished from among the larvae which had no pig- 

 ment spots either on the dorsal or ventral edges 

 of the trunk (similar to yellowfin), primarily by 

 the locality (between 10° N. and 25° N.) and time 

 of capture, relative body width, and pigmentation 

 on the tips of the jaws. 



Regarding locality and time of capture, 

 it was suggested that care should be taken not to 

 rely too heavily on latitudinal distance from the 

 Equator as a determining factor in species iden- 

 tification, because surface water temperature 

 in the western Pacific is high even in high lati- 

 tudes during summer and fall, so that, if spawn- 

 ing or larval survival were dependent upon 

 temperature in any way, then latitudinal desig- 

 nation might become meaningless. 



The second paper had for identifying the 

 various species a different approach. Identifi- 

 cation was based on locality and time of capture 

 and the number of spawning species present, as 

 represented in longline catches for similar 

 months. Pigmentation on the dorsal and ventral 

 edges of the trunk and the position of the second 

 dorsal fin insertion, in the case of two species 

 (T. orientalis and T. tonggol ) , also were used. 



Results of X-ray technique failed, of 

 course, to corroborate either view regarding 

 the presence or absence of pigment spots on the 

 trunk. Since a large percentage of specimens 

 had no pigment spots and about 25 percent had 

 either one spot on the dorsal edge, or one spot 

 on the ventral edge, or one spot each on both 

 dorsal and ventral edges of the trunk, it was 

 felt that, although pigmentation is useful in iden- 

 tifying larvae, there may be enough variation so 

 that other characters should also be used. 



