Growth characteristic of statolith of Todarodes pacificus in the Sea of Japan during the winter of an El-Nino year

Todarodes pacificus is one of the most abundant cephalopod resources in the Northwest Pacific Ocean. Understanding of its fishery ecology is the basis for sufficient exploitation of this resource. Statolith are a vital material for studying the age and growth, population structure and life history of cephalopods. The morphological growth patterns of statoliths of T. pacificus was studied for the first time using samples collected in the Sea of Japan by Chinese squid jigging fishery fleets in December 2018 (an El-Nino period). The results indicated that the dorsal dome, lateral dome and wing dome of the statoliths were relatively large and the rostrum dome was relatively small. The result of principal component analysis indicated that the total statolith length (TSL), lateral dome length (LDL), wing length (WL) and maximum width (MW) could be used as morphological parameters to study the morphological growth of statolith. The analysis of covariance (ANCOVA) indicated that there was no significant difference in the relationships between these morphological parameters versus mantle length (ML) and body weight (BW) in different genders. Based on the result of the Akaike’s information criterion (AIC), the relationships between ML, BW and TSL, LDL, MW were best described by power functions growth models, but linear function growth models were more effective for WL. The absolute morphological growth of statolith was gradually decreased, while the relative morphological growth of statolith was maintained steadily with increasing individual growth. This research not only provides reference for study of life history of T. pacificus thorough statolith, but also provides scientific basis for growth pattern of hard tissues of cephalopods under the effect of extreme weather patterns.