Application of a continuous time delay-difference model for the population dynamics of winter-spring cohort of neon flying squid (Ommastrephes bartramii, Lesueur 1821) in the North-west Pacific Ocean

A continuous time delay-difference model (CD-DM) was applied to the Chinese neon flying squid ( Ommastrephes bartramii ) jigging fisheries data (2001–2004) in the north-west Pacific Ocean. The continuous time delay-difference model (CD-DM) was modified from the discrete-time delay-difference model (D-DM), in which recruitment, growth and mortality rates are treated as varying continuously over time. Some commercially important stocks, such as shrimp and O. bartrami with recruitment, growth and mortality rates all varying continuously over time, may be better analysed by a continuous delay-difference model. We estimated the growth and recruitment of O. bartramii on the basis of the CD-DM, and biological reference points (BRPs) and accuracy of estimates are discussed in this study. We obtained population sizes of 183.9–201.8 million squid during early September 2004. The status of the stock was not in a sustainable state at this time with the available data, which suggests that measures should be taken for the sustainable utilization of this stock. The ability to calculate reference points without need of a full age-structured data makes CD-DM an attractive option for data-poor fisheries. We provided an alternative method for assessing O. bartramii stock and bridged the gap between simple surplus production models and complex fully age-structured models.