Natal origin of Pacific bluefin tuna from the California current large marine ecosystem

Natal origin of subadult (age-1) Pacific bluefin tuna (PBT, Thunnus
orientalis) from the California Current Large Marine Ecosystem (CCLME) was
determined using natural tracers in ear stones (otoliths). Age-0 PBT
collected from the two known spawning areas in the western Pacific Ocean
(East China Sea, Sea of Japan) were used to establish baseline signatures
from otolith cores over four years (2014-2017) based on a suite of trace
elements (Li, Mg, Mn, Sr, Zn, and Ba). Distinct chemical signatures
existed in the otolith cores of age-0 PBT collected from the two spawning
areas, with overall classification accuracy ranging from 73-93% by year.
Subadult PBT collected in the CCLME over the following four years
(2015-2018) were then age-class matched to baselines using mixed-stock
analysis. Natal origin of trans-Pacific migrants in the CCLME ranged from
43-78% from the East China Sea and 22-57% from the Sea of Japan,
highlighting the importance of both spawning areas for PBT in the CCLME.
This study provides the first estimates on the natal origin of subadult
PBT in this ecosystem using otolith chemistry and expands upon the
application of these natural tracers for population connectivity studies
for this species.