Beak length analysis for the identification of two morphologically similar species common names Uroteuthis edulis (Hoyle, 1885) and Uroteuthis duvaucelii (D'Orbigny, 1835) (Cephalopoda: Loliginidae) in the southern East China Sea

In this study, beak length characteristics were described and used to predict the individual size and separate 2 morphologically similar species of the family Loliginidae: Uroteuthis edulis and Uroteuthis duvauceli. The samples were collected using bottom trawl methods in May, September and December from the southern East China Sea in 2015. The data presented here indicates that identification was possible with a high accuracy using various ratios of beak lengths indices. Differences were observed among various length indices and the corresponding ratios. Also, the beak length indices were affected presumably due to the individual growth of each specimen. Additionally, relationships between a durable beak measurement versus both mantle length (ML) and body weight (BW) were studied. Rostral length (RL) linearly increased with ML and BW. The beak lengths did not change with the fluctuation of the ML. Significant differences (P < 0.05) were observed between 5 upper beak ratios and 6 lower beak ratios. The data presented here indicated that beak ratios could be used as a variable to identify the two species in a stepwise discriminant analysis. Additionally, linear discriminant functions of upper and lower beak morphological variables were developed for the two loliginids. The data presented here indicate results that have a high level of correctness in species classification.