Feeding habits of neon flying squid Ommastrephes bartramii in the transitional region of the central North Pacific

We examined the feeding habits of the neon flying squid Ommastrephes bartramii from late spring to mid-summer in relation to its northward migration in the transitional waters of the central North Pacific. The winter-spring cohort (ca. 15 to 25 cm in May and 20 to 35 cm in July) and the autumn cohort (ca. 30 to 45 cm in May and 35 to 50 cm in July) were identified by their dorsal mantle lengths. In May and July, the winter-spring cohort was distributed only in the transition zone (TZ) south of the subarctic boundary. This cohort preyed primarily on crustaceans such as euphausiids and amphipods in May, but in July, their primary prey shifted to the sternoptychid fish Maurolicus imperatorius. In May, the larger-sized autumn cohort was also distributed only in the TZ, but in July, these individuals migrated to the transitional domain (TD) north of the subarctic boundary. The main prey of the autumn cohort were micronektonic animals that dominated the TZ in May: the transitional-water myctophid Symbolophorus californiensis, and 2 subtropical myctophids, Ceratoscopelus warmingi and Electrona risso. Secondary important prey items included the transitional-water squid Onychoteuthis borealijaponica and subarctic gonatid squids such as Gonatus berryi and Berryteuthis anonychus. In July, the main prey species in the TD were S. californiensis and O. borealijaponica, both of which also migrated from the TZ into the TD, crossing the subarctic boundary in summer. We estimated the feeding impact of the autumn squid cohort on myctophids in the TD during summer.