Global population structure of 
yellowfin tuna, Thunnus albacares, 
inferred from allozyme and 
mitochondrial DIMA variation 
Robert D. Ward 
Nicholas G. Elliott 
Bronwyn H. Innes 
Adam J. Smolenski 
Peter M. Grewe 
CSIRO Division of Marine Research 
GPO Box 1538, Hobart, Tasmania 7001, Australia 
E-mail address (for Robert Ward): Bob.Ward@marine.csiro.au 
Abstract .—Yellowfin tuna, Thun- 
nus albacares, were sampled from one 
region of the Atlantic Ocean, two re- 
gions of the Indian Ocean, and six re- 
gions of the Pacific Ocean. One of the 
Indian Ocean collections could not be 
allozymically analyzed; the remaining 
eight collections were examined for four 
polymorphic allozyme loci (ADA*, FH*, 
GPI- A*, and GPI-B*, rc=540 to 677). All 
nine collections were examined for mi- 
tochondrial DNA variation (n= 767), 
with two restriction enzymes (Bel I and 
Eco RI ) that detect polymorphic restric- 
tion sites in yellowfin tuna. Allele fre- 
quencies at three of the allozyme loci 
were homogeneous across collections, 
whereas GPI-A* showed highly signifi- 
cant differentiation (PcO.OOl). The 
GPI-A* data, taken together with the 
geographic location of the collections, 
suggested the existence of at least four 
yellowfin tuna stocks: Atlantic Ocean, 
Indian Ocean, west-central Pacific 
Ocean, and east Pacific Ocean. Mito- 
chondrial DNA differentiation was 
more limited, but spatial heterogene- 
ity of the 24 observed haplotypes over 
the nine regions (P=0.048) and three 
oceans (P=0.009) was significant. The 
mtDNA data did not differentiate west- 
central Pacific Ocean collections from 
east Pacific Ocean collections but did 
support the separation of Atlantic 
Ocean, Indian Ocean, and Pacific Ocean 
stocks. 
Manuscript accepted 10 February 1997 
Fishery Bulletin 95:566-575 (1997). 
The yellowfin tuna, Thunnus alba- 
cares (Bonnaterre), supports impor- 
tant fisheries in tropical and sub- 
tropical oceans. Catches have in- 
creased from about 600,000 metric 
tons (t) in 1982 and 1983 to about 
1,100,000 t in 1993 and 1994; in 
1994, about 63% of the catch came 
from the Pacific Ocean, about 24% 
from the Indian Ocean, and 14% 
from the Atlantic Ocean (FAO, 
1996). Given the size and circum- 
global nature of the resource, there 
is considerable management inter- 
est in determining stock structures. 
It is only comparatively recently 
that yellowfin tuna has been recog- 
nized as a single species (Gibbs and 
Collette, 1967); its high degree of 
morphological variation led Jordan 
and Evermann (1926) to recognize 
seven yellowfin tuna species. How- 
ever, a major morphometric study by 
Royce (1964) revealed that intra- 
oceanic differences could be greater 
than interoceanic differences and 
that several characters showed cli- 
nal variation. He concluded that the 
morphometric data are best ex- 
plained by a single worldwide pan- 
tropical species, a conclusion con- 
firmed by Gibbs and Collette ( 1967). 
Most stock structure studies of 
yellowfin tuna have focused on the 
large Pacific Ocean component of 
the catch. Here, tagging experi- 
ments indicated that yellowfin tuna 
usually migrate hundreds rather 
than thousands of kilometers and 
that their movements do not range 
far both east-west or north-south 
(Joseph et al., 1964; Bayliff, 1979; 
Hunter et al., 1986; Lewis, 1992). 
Morphometric studies have pro- 
vided commensurate results, with 
Mexico and Ecuador fish being 
much more similar to one another 
than to fish from the central (Ha- 
waii) and western (Australia, Ja- 
pan) Pacific (Schaefer, 1991). Stud- 
ies of the microchemical composi- 
tion of larval portions of otoliths in 
West Pacific fish (Indonesia, Phil- 
ippines, Coral Sea, Hawaii) have 
shown some differences, indicating 
that such analyses may be useful in 
determination of spawning origins 
(Gunn and Ward 1 ; Gunn 2 ). Genetic 
studies of four to five polymorphic 
1 Gunn, J. S„ and R. D. Ward. 1994. The 
discrimination of yellowfin tuna sub-popu- 
lations within the AFZ. Phase 1: a pilot 
study to determine the extent of genetic 
and otolith microchemical variability in 
populations from different parts of the Pa- 
cific and Indian Oceans. Final Report (91/ 
27) to Fisheries Research and Development 
Corporation, Deakin, ACT, Australia. 
2 Gunn, J. S. 1996. CSIRO Division of 
Marine Research, Hobart, Tasmania, 
Australia. Unpubl. data. 
