Annual Variability in the Horizontal Distribution and Biological Characteristics of the Neon Flying Squid Ommastrephes bartramii in the Central North Pacific Ocean in the Early Summer Between 2011 and 2019

To clarify the effect of the oceanographic conditions on the distribution of the neon flying squid Ommastrephes bartramii in the central North Pacific, we examined the mantle length composition, sex, maturity, and age in days of the squid caught from late June to early July during 2011–2019. Squid were collected using a non-size-selective research driftnet at seven sampling stations situated along 175° 30’ E and between 35° 00’ N and 45° 00’ N. The autumn cohort females were mainly distributed in the northern part of the study area, whereas the autumn cohort males and the winter–spring cohort squid were distributed in the southern part of the study area. The proportion of the autumn cohort males to the total males fluctuated annually. At the southernmost sampling station where the autumn cohort males were mainly caught, a strong positive correlation was observed between the mean sea surface temperature from mid-May to late-May and the proportion of the autumn cohort males to the total males each year. These findings suggest that the distribution of the autumn cohort males changed with oceanographic conditions, and high sea surface temperature before the survey period studied in subarctic waters caused a northward shift of the distribution of the autumn cohort males. In contrast, no strong correlation was observed between the distribution of the autumn cohort females or the winter–spring squid and oceanographic conditions probably because oceanographic conditions in their horizontal distribution ranges did not vary greatly among the survey years.