Linkages between Japanese sardines and gyre spin-up Shoshiro Minobe (Hokkaido University)

Data & Method Data –Log Residual Recruitment for Japanese sardine, Pacific group (e.g., Yatsu et al FO) calculated by Dr. Honda RPS (ReProductive Success) with correction due to density effect –NCEP-NCAR reanalysis data –Our own subsurface temperature data from WOD m averaged temp (similar to sea-level height) –Satellite altimeter data Method –correlation –Linear Rossby wave model At each latitude, sea-level heights due to Rossby waves propagating westward are calculated from wind-stress curl

Feeding ground (summer) Nursery ground (spring) Spawning ground (winter-early spring) Schematics of areas for Sardine, Pacific group, low-stock level period.

Simultaneous correlation bewteen LNRR and SST DJF SST と同年の LNRR との相関 R < -0.4 over DJF KESA SST & LNRR Kuroshio extension southern region (KESA) SST explains well sharp decrease of LNRR in the end of 1980s. Noto & Yasuda (1999) suggested KESA SST controls sardine mortality (close to RPS) for the period Warm SST  shallower mixed layer  bad nutrient supply  larger mortality.

Simultaneous correlation bewteen LNRR and SST DJF SST と同年の LNRR との相関 R < -0.4 over DJF KESA -SST & LNRR Kuroshio extension southern region (KESA) SST cannot explain increase of LNRR in the 1960s and relatively large LNRR after 2005 SST explains well sharp decrease of LNRR in the end of 1980s. Noto & Yasuda (1999) suggested KESA SST controls sardine mortality (close to RPS) for the period Warm SST  shallower mixed layer  bad nutrient supply  larger mortality.

2005 年前後の SST 変化 DJF SST minus KESA あるいは近隣の海域で SST は下がっていない

0-400 m averaged temp & LNRR Recent increase may also be explained (insufficient data in recent years). Subsurface temp explains 1960s LNRR increase. Nishikawa & Yasuda (1999) suggested current speed is important for mixed layer based on OFES (ocean model) for the period Faster current  short resident time of water in Kuroshio Extension  shallower mixed layer  bad nutrient supply  larger mortality.

LNRR ： SST & 0-400m temp Corr. DJF SST & LNRR DJF KESA -SST & LNRR Rossby waves? Corr temp & LNRR Subsurface temp explains LNRR better than KESA SST. KESA m -temp & LNRR (r=0.63)

Eastward velocity anomalies to the west of eastward wind stress anomalies with a time-lag of Rossby wave propagation.

Lag correlation: Eastward wind-stress & LNRR Westward wind stress anomalies leading to high LNRR is consistent with Rossby wave hypothesis.

Rossby waves? Correlation in sea-level height between satellite altimeter SLH & Rossby model (Qiu 2003) Kuroshio extension west of 160E cannot explained ロスビー波モデル Not only KESA temperature south of Japan is also related as a gyre spin-up & down?

Correlations onto LNRR with Sea- level height and zonal velocity But this is in the region where Rossby wave model fails.

Sea surface height EOF1 (Satellite) Prominent decadal variability. Jet-trapped Rossby waves (thin-jet theory) might play a role. Lag correlation between PC1 and Sea surface height.

Conclusions Reproductive success expressed by LNRR for the Japanese sardine Pacific group is highly correlated with subsurface temperature in the Kuroshio extension southern area and in western subtropical gyre. It is interesting study in future whether gyre spin-up/down in addition to local speed up/down of the Kuroshio extension play an important (e.g., by transporting low-nutrient waters from the south).