Age and growth of the short-finned squid Illex coindetii in Galician waters (NW Spain) based on statolith analysis

Abstract

Age and growth of Illex coindetii in the fishery northwest of Spain were estimated from statolith growth increments. 341 statoliths were examined (170 males, 171 females) from individuals of 48–379 mm mantle length (ML). The maximum size of squids was 279 mm ML for males and 379 mm ML for females. Weight-at-length of mature males was greater than that of immature males and mature and immature females. Lifespan was estimated at 13 months for males and 15 months for females. Recruitment to the fishery occurred approximately at three months of age. Mantle length instantaneous relative growth rates were 0.72 mm d⁻¹ for males and 0.84 mm d⁻¹ for females. Weight growth rate was 2.22 g d⁻¹ for males and 3.66 g d⁻¹ for females. Maturity stages, however, influenced increase in weight in both sexes, such that weight-at-age was greater for mature than for immature individuals. The age at which individuals mature is variable, ranging from 140 to 271 d in males and between 183 and 285 in females. Growth rates in both sexes were dependent on the season of hatching. Squids hatched in winter attained larger sizes for the same age than squids in other seasons. These seasonal differences in growth were only evident after squids had reached 8 months of age. Reading daily increments in statoliths seems to be a reliable technique for studying the age and growth of Illex coindetii.