Influence of oceanic climate variability on stock level of western winter–spring cohort of Ommastrephes bartramii in the Northwest Pacific Ocean

ABSTRACT: The western winter–spring cohort of Ommastrephes bartramii exhibited dynamic stock level associated with concurrent shifts in the Pacific Decadal Oscillation (PDO) during 2002–2011. To explore the potential mechanism on regional oceanic conditions related to the large-scale PDO phenomenon affecting O. bartramii stocks, we examined variations in the environmental condition on the spawning ground for recruitment, spatial distribution of fishing effort, and habitat hotspots on the fishing ground during different PDO phases. The PDO was found to be highly correlated with the biophysical environmental conditions on the spawning and fishing grounds of O. bartramii. The suitable spawning zone (SSZ) considered as an indicator of incubation condition was not sufficient to explain the recruitment variability. However, the changing chlorophyll a (Chl-a) concentration induced variations in feeding condition for squid paralarvae and juveniles, primarily influencing the O. bartramii recruitment. Comparing to the cold PDO phase, high frequency of fishing effort occupied the regions with lower sea surface temperature (SST) and relatively enhanced Chl-a concentration during the warm PDO phase. The location of fishing efforts tended to be intensive and shifted westward and northward in the cold PDO phase. Moreover, the warm PDO yielded prominently enlarged squid habitat hotspots. This study suggests that stock level of western winter–spring cohort of O. bartramii can be explained by the local environmental conditions including the food availability on the spawning ground, SST, and Chl-a concentration on the fishing ground affecting squid spatial distributions, which could be reflected by the PDO climate variability in the Northwest Pacific Ocean.