Abstract
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 4 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 73–93% by year. Subadult PBT collected in the CCLME over the following 4 years (2015–2018) were then age-class matched to baselines using mixed-stock analysis. Natal origin of trans-Pacific migrants in the CCLME ranged 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.
Highlights
Characterizing population dynamics and connectivity for highly migratory species remains challenging, especially for species that cross ocean basins
In the western Pacific, there have been multiple efforts to identify natal origin, all capitalizing on the difference in spawning time between the two spawning areas
Shiao et al [6] measured oxygen isotopes from the otolith core to the margin, which became enriched as temperatures cooled in the winter and resulted in an earlier increase in otolith oxygen values for fish spawned in the Sea of Japan (SoJ) relative to ECS
Summary
Characterizing population dynamics and connectivity for highly migratory species remains challenging, especially for species that cross ocean basins. Pacific bluefin tuna (PBT, Thunnus orientalis) is widely distributed throughout the North Pacific Ocean and western South Pacific Ocean [1,2], the dynamics within this range are not well understood and uncertainties about stock structure continue to complicate fisheries management [3]. PBT is managed under the assumption of a single stock in the Pacific Ocean with two discrete spawning areas in the western Pacific Ocean (WPO). One located around the Philippines north to the Ryukyu Islands incorporating both the Philippines Sea and East China Sea (hereafter: East China Sea, ECS) with spawning occurring from royalsocietypublishing.org/journal/rsbl Biol.
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