Effects of marine environment variation on the growth of neon flying squid (Ommastrephes bartramii) in the north Pacific Ocean

The neon flying squid (Ommastrephes bartramii) is a dominate economic species in the north Pacific Ocean. Marine environment variation has a profound impact on the marine organisms and their growth. As a short lifespan oceanic cephalopod, O. bartramii is highly susceptible to the climate change in different degrees, such as the Pacific Decadal Oscillation (PDO), El Niño and La Niña. Consequently, investigation on growth of O. bartramii affected by variable marine environment becomes an important and basic part for cephalopod research. Based on 6091 samples of O. bartramii collected in fishing season (from August to October) from 2009 to 2012 and 2015 to 2016 in the north Pacific Ocean, the growth of O. bartramii was studied combined with the marine environmental factors in the present study. The results indicated that significant difference of fishery biological characteristics was found between different gender and marine environment years. Viewed from the difference of the dominated mantle length (ML) and body weight (BW) group, maximum values of both ML and BW occurred in 2016, while minimum values occurred in 2010 and 2015. The b values of ML-BW relationship in all sampling years were significantly different with 3, which showed allometric growth. The mature stage of both female and male squids concentrated in stage II, and the proportion of mature female squid was less than that of male squids. The maturation of ML of O. bartramii was positively correlated with the Pacific Decadal Oscillation index with one-year lag. Samples in El Niño years were greater than those in La Niña years, and individuals in El Niño year with very strong intensity were the smallest. The El Niño event with very strong intensity caused low sea surface temperature (SST) and low Chlorophyll a (Chl. a) concentration which was not beneficial to the growth and their gonad development of O. bartramii. Higher SST and Chl. a concentration provided favorable environment for O. bartramii, resulting in a greater body size and early maturation. The present study suggested that the growth and gonad development had significant difference among different marine environment years, and the synthetic actions of PDO, El Niño/La Niña, SST and Chl. a concentration were the dominate factors that affected the growth of O. bartramii.