Age, growth and maturation of Illex coindetii (Cephalopoda: Ommastrephidae) in the eastern Adriatic Sea

Analysis of statolith growth increments was used to determine age and describe growth pattern of broadtail shortfin squid Illex coindetii in the central eastern Adriatic Sea, an important demersal resource in the Adriatic basin. Size-at-age data were obtained from a large sample (N = 476, including 249 males and 227 females) of individuals with dorsal mantle length (ML) from 55 to 216 mm and body weight (BW) from 5.7 to 356.9 g. Estimated age ranged from 52 to 186 days, with an average of 108 days, suggesting the species has a life span of six months. No statistically significant difference in statolith length was found between the sexes. The back-calculation analysis showed that Adriatic I. coindetii hatches continuously throughout the year, with two alternative spawning periods, in summer and winter. Therefore, a generation born in summer reproduces in winter, and generation born in winter reproduces in summer. Hatchlings of the autumn–winter period were significantly larger and heavier with slower growth than their offspring hatched in summer and spring that exhibited faster growth and matured at younger age. Estimated age at first maturity were 137.4 and 109.2 days, for females and males, respectively. Growth was best described by Schnute and logistic model that display asymptotic tendencies by the end of the life span. There were no major differences in growth pattern between different cohorts of each sex, with faster growth recorded at younger age.