Inference on the stocks relationship of neon flying squid (Ommastrephes bartramii) in the North Pacific based on demographic analysis

• Main Authors: CHIH-SHIN CHEN, 陳志炘
• Other Authors: TAI-SHENG CHIU
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/25233032333420406780

博士 === 國立臺灣大學 === 動物學研究所 === 91 === The neon flying squid, Ommastrephes bartramii (Lesueur), is a widespread oceanic squid, ranged from subtropical to temperate zones. In this study, tempo-spatial distribution patterns of the squid were extracted from catch analysis, based on the data set of 1986 - 2000. Demographic parameters, which included hatching date and growth pattern, were estimated from statolith microanalysis, based on squid samples taken from 1997 — 1998. In general, the species is subdivided into 2 stocks geographically and 2 cohorts seasonally in the North Pacific, and each group can be characterized by specific traits. Finally, I propose a migration model for the species, in order to linking the demographic differences to the prevailing North Pacific temperature regimes. The evidences that support my proposition are followed. 1. In the catch statistics analysis, there are apparent two interrupted fishing grounds of NE and NW, demarcated by a longitudinal line around 165°- 170°E. The CPUE scatter plots indicated that high concentration of squid was located at 40°N in the NE, while it shifted to 44°- 45°N in NW. 2. By principal component analysis on the CPUE’s and environmental factors, I found two scatter groups corresponding to the NE and NW stocks. In the meanwhile, higher abundance of the squid in the NE Pacific was correlated to water temperature and salinity, and further that water temperature had higher estimation power to locate a higher abundance site. The concentration of squid in the North Pacific was also associated with the strength of the Subarctic Front Zone. 3. By back-estimation of hatching dates, calculated from statolith daily counts, two geographical population of O. bartramii had two distinguishable hatching seasons. Two cohorts of autumn and winter were identified in the northeastern (NE) North Pacific, while only a comparable winter cohort was distinctive in the northwestern (NW). The seasonal cohorts illustrated by large-sized female can be separated by a size at 350 mm mantle length. 4. By fitting the ML-at-age into various growth functions, we found the growth pattern varied among groups. The NE small females and males, and NW large females grew innately as fitted by a power function; however, NE large females, and NW small females and males decreased their growth rate gradually as described by Gompertz function. Finally, a large-scale migration pattern of O. bartramii in the North Pacific was considered collectively: the squid spawning in the Subtropical Domain and feeding in the Subarctic Front Zone in general. Further detailed that the NW-S female and male squids migrate a short route, as they encounter lower temperature at their earlier life. Longer migratory route is possibly for large females as they experienced longer life span (> 230 d and > 350 mm ML). Indistinguishable growth parameters shown by NE and NW large females suggest a bifurcating population originated from eastern North Pacific, and part of the population migrates across the geographic boundary at a longitude of 170°E.