14:05 〜 14:20
[AOS13-14] Vertical habitat shifts of juvenile Japanese jack mackerel (Trachurus japonicus) estimated by otolith microchemistry
キーワード:耳石、耳石酸素安定同位体比、マアジ、鉛直生息層変化、初期生活史、東シナ海
Japanese jack mackerel (Trachurus japonicus) are distributed in the semi-demersal layer, while larvae are distributed in the surface layer in the East China Sea. Smooth vertical habitat layer shift (HLS) is important for their survival. However, details (start timing and duration) of HLS have been unclarified. To elucidate HLS, otolith oxygen stable isotope ratio (δ18Ooto), of which the value increases at lower temperature and higher salinity, was analyzed in high resolution by 5 days segment. From the history of δ18Ooto, HLS timing was estimated by two types of indices; HLS moment and HLS duration, which were identified by the largest δ18Ooto gap signal and gradual δ18Ooto change, respectively. In addition, daily ages and water temperature variances fish experienced were compared among three life history traits; the metamorphosis, the behavioral change from planktonic to self-swimming and the swimming ability increase. As a result, average HLS moment was estimated to be 42.2±18.2 daily age. HLS started at 28.0±11.0 daily age and average HLS duration was 27.9±16.2 days on average. The start of HLS duration corresponded to the start of metamorphosis, and development of swimming ability was happened simultaneously with HLS moment. From the δ18Ooto value of edge, observed temperature and salinity in the layer fish caught and the relationship between salinity and δ18Osw (δ18O of sea water) from the previous study, an equation between δ18O (δ18Ooto − δ18Osw) and temperature was estimated; Temperature(°C) = −3.51 (±0.49) × δ18O (‰) + 15.86 (±0.29). Temperature variance converted from δ18Ooto suggested that juveniles gradually shift habitat layer as they experience early life history traits, not suddenly after specific trait.