Age, growth and population structure of jumbo flying squid Dosidicus gigas off the Peruvian Exclusive Economic Zone based on beak microstructure

The beak is a hard structure of cephalopods with relatively constant shape, which records a lot of biological and ecological information. Based on samples collected by Chinese squid jigging vessels off the Peruvian Exclusive Economic Zone from July to October 2013, we explored the feasibility of age estimation and growth pattern with the upper beak of Dosidicus gigas. The internal rostral axis and longitudinal increments could be clearly identified on the upper beak rostrum sagittal sections of this species. Checks and abnormal structure were observed in some beaks. Ages estimated were from 123 to 298 days for females and from 106 to 274 days for males. Back-calculated hatching dates were from December 2012 to May 2013. All of the samples were from the austral summer/autumn spawning cohort. Hatching peak occurred between January and March. Growth in mantle length (ML) and body weight were best described by exponential functions and there were no significant differences between females and males. The maximum absolute daily growth rate and instantaneous growth rate of ML were 2.12 mm/day and 0.59/day, respectively. This study suggests that the upper beak could be used for estimating age, growth and population structure of D. gigas.