Variations of life history parameters in two geographical groups of the neon flying squid, Ommastrephes bartramii, from the North Pacific

Abstract

The neon flying squid, Ommastrephes bartramii (Lesueur), is a widespread subtropical to temperate species, and is composed of several tempo-spatial groups in the North Pacific. We analyze the growth parameters of two allopatric stocks with two seasonal cohorts using statolith microstructure, and propose a tempo-spatial migration model. We used 571 statoliths, obtained from juvenile/adult squids (175–527 mm mantle length, ML). Based on precise digitized statolith growth marks, various early life demographic traits were estimated by the back-calculation method. Two cohorts of autumn and winter were identified in the northeastern (NE) North Pacific, while only a comparable winter cohort was found in the northwestern (NW). There was a significant difference in the relationships of statolith radius (Ra) to increment numbers (In) between NE and NW stocks. However, linear ML to Ra relationship exhibited no geographic difference in large females (>350 mm ML), but significant difference between NE and NW in both small females (<350 mm ML) and males. Growth in length (ML) at week ( t) is best fitted by a power function of innate growth for NE small females and males, and NW large females; however, the Gompertz function of decreasing growth rate is better for NE large females, and NW small females and males. Variations on demographic traits confirm two geographic stocks of NE and NW, and two seasonal cohorts of NE stock. Indistinguishable growth parameters shown by NE and NW large females suggest a longer life history of the population, which migrates across the geographic boundary at a longitude of 170°E. The ambient temperature, that corresponding to their early life stages, could be a plausible factor in later growth difference.