Age and growth patterns in squid Berryteuthis magister and B. septemdentatus

The purpose of the study was to reveal differences in age and growth patterns in two closely related species: Berryteuthis septemdentatus from the Japan Sea and schoolmaster gonate squid B. magister from the Bering Sea based on the analysis of age determining structures such as statoliths. Methods included preparation and processing of statoliths (extraction, gluing and grinding) and counting increments (growth lines) followed by further statistical analysis of daily increments and obtaining characteristics of squids’ age and growth. Results suggested that there were species-specific patterns in growth rates of these two squid species. It appeared that, at earlier ontogenetic stages, growth rates in B. septemdentatus are higher than in B. magister; however, at later ontogenetic stages, individuals of B. magister grow faster than B. septemdentatus. Discussion on the revealed differences in growth patterns between these two morphologically and phylogenetically close species suggested that higher growth rates in B. septemdentatus at earlier ontogenetic stages might be related to larger size of ripe eggs and, henceforward, to larger size of newly hatched paralarvae. However, as the squid grow, growth rates in B. septemdentatus become slower than in B. magister presumably due to colder deepwater habitat in the Japan Sea for the former species compared to deep-sea areas occupied by the latter species. Scientific novelty includes new information on growth rates and age in B. septemdentatus and its comparison with those in the schoolmaster gonate squid B. magister as revealed by the analysis of age-recording structures (statoliths), and the use of relatively large size range of B. septemdentatus with mantle length from 141 to 203 mm.