ON THE CLARIFICATION OF LARVAL TUNA IDENTIFICATION 



PARTICULARLY IN THE GENUS Thunnus ^ r.A v 



Walter M. Matsumoto,^ Elbert H. Ahlstrom,'' S. Jones,^ 

 WiTOLD L. Klawe,* William J. Richards/ and Shoji Ueyanagi" 



ABSTRACT 



A Larval Tuna Identification Workshop was held at the Bureau of Commercial Fisheries Biological 

 Laboratory (now the National Marine Fisheries Service, Southwest Fisheries Center), Honolulu, 

 Hawaii, on March 2-6, 1970, to resolve conflicting views on the identification of larvae of Thunnus 

 alalunga and T. albacares and to clarify the status of larval identification of other Thunnus species. 



The identification of T. alalunga (Yabe and Ueyanagi, 1962), T. albacares (Matsumoto, 1958), T. 

 obesus (Matsumoto, 1962), and T. thynnus (Yabe, Ueyanagi, and Watanabe, 1966) was agreed upon 

 as correct, except that the description of T. albacares should include the appearance of black pigmen- 

 tation at the tip of the lower jaw when the larva attains a length of about 4.5 mm SL and that the 

 lower size limit of reliable identification of T. alalunga be set at about 4.5 mm SL until further studies 

 indicate more precisely whether the black pigmentation at the tip of the lower jaw in T. albacares 

 appears earlier. There was no difference in appearance of T. thynnus larvae from the Atlantic and 

 Indo-Pacific Oceans. The identification of T. tonggol and T. maccoyii larvae was not conclusive. The 

 larvae of T. atlanticus required further study. 



The workshop further concurred that juveniles (13-200 mm SL) of several species of Thunnus may 

 be separated by internal and external characters: T. atlanticus by vertebral count, T. alalunga by 

 shape of first elongate haemal spine and arrangement of pterygiophores of the second dorsal fin rel- 

 ative to two adjacent neural spines, and T. thynnus by configuration of lateral line and arrangement 

 of pterygiophores of the second dorsal fin; and that juveniles of T. obesus and T. albacares may be sep- 

 arated from the previous three species by arrangement of pterygiophores of the second dorsal fin, but 

 not from each other. 



The proper identification of larval tunas has 

 been a perplexing and difficult problem for many 

 years. Although progress in the past two dec- 

 ades has resulted in agreement on the identifica- 

 tion of larvae of a number of species {Katsu- 

 womis pelamis, Euthyymus alletteratus, E. af- 

 finis, E. lineatus, Thimnus thynnus, T. obesus, 

 and Auxis spp.) , there is still some disagreement 



^ National Marine Fisheries Service, Southwest Fish- 

 eries Center, Honolulu, HI 96812. 



^ National Marine Fisheries Service, Southwest Fish- 

 eries Center, La Jolla, CA 92037. 



^ Department of Zoology, University College, Trivan- 

 dum-1, India. (Formerly: Central Marine Fisheries 

 Research Institute, Mandapam Camp, South India.) 



* Inter-American Tropical Tuna Commission, La Jolla, 

 CA 92037. 



^ National Marine Fisheries Service, Southeast Fish- 

 eries Center, Miami, FL 33149. 



* Far Seas Fisheries Research Laboratory, Shimizu, 

 Japan. 



and confusion on the identity and description of 

 T. alalunga and T. albacares. At the present 

 time there are two diflferent descriptions given 

 for T. alalunga (Matsumoto, 1962; Yabe and 

 Ueyanagi, 1962). The identity of other tunas, 

 such as T. tonggol, T. maccoyii, and T. atlanticus, 

 has yet to be confirmed or resolved. 



One of the chief problems in larval tuna iden- 

 tification is the difficulty in obtaining good series 

 of larvae for study. Tuna larvae are seldom 

 taken in sufficient numbers by the usual collect- 

 ing methods, and individuals over 10 mm stan- 

 dard length (SL) are taken rather infrequently. 

 Additionally, although the young of a number 

 of tuna species are found together in many parts 

 of the ocean, some species are localized in certain 

 areas. Consequently, it is extremely difficult for 

 workers in diflferent parts of the world to have 



Manuscript accepted September 1971. 



FISHERY BULLETIN; VOL. 70, NO. I, 1972. 



