Natal origin and age-specific egress of Pacific bluefin tuna from coastal nurseries revealed with geochemical markers

Abstract

Geochemical chronologies were constructed from otoliths of adult Pacific bluefin tuna (PBT) to investigate the timing of age-specific egress of juveniles from coastal nurseries in the East China Sea or Sea of Japan to offshore waters of the Pacific Ocean. Element:Ca chronologies were developed for otolith Li, Mg, Mn, Zn, Sr, and Ba, and our assessment focused on the section of the otolith corresponding to the age-0 to age-1 + interval. Next, we applied a common time-series approach to geochemical profiles to identify divergences presumably linked to inshore-offshore migrations. Conspicuous geochemical shifts were detected during the juvenile interval for Mg:Ca, Mn:Ca, and Sr:Ca that were indicative of coastal-offshore transitions or egress generally occurring for individuals approximately 4–6 mo. old, with later departures (6 mo. or older) linked to overwintering being more limited. Changepoints in otolith Ba:Ca profiles were most common in the early age-1 period (ca. 12–16 mo.) and appear associated with entry into upwelling areas such as the California Current Large Marine Ecosystem following trans-Pacific migrations. Natal origin of PBT was also predicted using the early life portion of geochemical profile in relation to a baseline sample comprised of age-0 PBT from the two primary spawning areas in the East China Sea and Sea of Japan. Mixed-stock analysis indicated that the majority (66%) of adult PBT in our sample originated from the East China Sea, but individuals of Sea of Japan origin were also detected in the Ryukyu Archipelago.

Reading the biomineralized book of life: expanding otolith biogeochemical research and applications for fisheries and ecosystem-based management

“…In fully marine settings and for highly migratory fish species with ocean-wide or cosmopolitan distribution such as tunas and billfishes, otolith chemistry has also been used to investigate nursery area use and contribution rates as well as adult movements (Artetxe-Arrate et al 2021;Fraile et al 2016;Rooker et al 2008Rooker et al , 2021Wells et al 2021). These species regularly cross management boundaries, often migrating large distances to complete their life cycles and some exhibiting homing behaviour that further complicates stock assessment and management efforts (Collette et al 2011).…”

Otolith geochemistry reflects life histories of Pacific bluefin tuna

“…To the extent that PBT move through geochemically distinct water masses and physiological influences on biomineralization can be accounted for, PBT otolith geochemical records could allow for reconstruction of migratory movements and identification of migratory contingents. Previous studies utilized otolith chemistry to characterize signatures of young-of-theyear PBT collected on spawning grounds [27,28], to determine natal origins of PBT that migrated to the EPO [29], to document discrete profiles of juveniles collected in the EPO [30], and assess the timing of juvenile emigration from the WPO [31]. However, studies documenting continuous life histories for large PBF otoliths collected over wide areas of the north and south Pacific are needed to better understand influences of physiology and water mass environmental conditions on otolith chemical time series.…”

Natal origin of Pacific bluefin tuna Thunnus orientalis determined by SIMS oxygen isotope analysis of otoliths

“…δ 18 O otolith generally displays a negative correlation with water temperature, with minor differences in fractionation factors among species. Using such temperature dependence of the δ 18 O otolith , many studies have taken advantage of this techniques to reconstruct migration histories [ 35 ], horizontal and vertical distribution [ 36 ], and population structure [ 1 , 25 , 37 ] of various fish species. Previous studies have successfully distinguished the eastern (the Mediterranean Sea) and western (the Gulf of Mexico) stocks of Atlantic bluefin tuna (ABT, Thunnus thynnus ) using differences in water temperature and salinity reflected on the δ 18 O otolith values deposited during the young-of-the-year (YOY) period between nursery areas [ 37 , 38 ].…”

“…After spending several years in the CCLME, mature PBT return to the western Pacific to spawn [21]. Species like PBT whose spawning occurs seasonally in geographically limited areas are particularly vulnerable to ocean warming as early growth and survival of their offspring often depends primarily on water temperature [22,23] coupled with prey availability [24], resulting in the interannual recruitment variability [25][26][27]. Despite its importance for proper stock assessment and management, such climate-induced variability in the recruitment of PBT from each spawning ground remains largely unknown due to difficulties in monitoring long-term responses to climate stressors.…”