Migration patterns and changes in hatching date of neon flying squid Ommastrephes bartramii distributed in the northwestern Pacific Ocean in early summer and caught in fishing grounds off the coast of northeastern Japan in winter

We examined specimens from the winter–spring cohort of the neon flying squid Ommastrephes bartramii caught off the coast of northeastern Japan in early summer and the following winter for mantle length, sex, maturity, and age to determine their hatching dates as well as their growth and migration patterns. Squid specimens were collected with a research driftnet in July 2018 in the northwestern Pacific and by squid jigging off the coast of northeastern Japan in November 2018 and January 2019. The ages of 300 specimens were estimated from statolith increment counts and used to back-calculate hatching dates. Hatching dates ranged from September 2017 to July 2018. The peak hatching dates varied with the survey season, even for the same winter–spring cohort. Squid caught in July 2018 hatched mainly from February to April, while those caught in November 2018 hatched mostly during April and May and those caught in January 2019 hatched principally during May and June. This pattern indicates that squid migrate among fishing grounds and that stocks are gradually replaced by late-hatching squid.