Akihiko Yatsu

Night‐time vertical distribution and abundance of small epipelagic and mesopelagic fishes in the upper 100 m layer of the Kuroshio–Oyashio Transition Zone in Spring

In order to simultaneously compare vertical distributions of small pelagic fishes and mesopelagic fishes during the night in the upper 100 m, one oblique and 11 horizontal tows of largesized (opening area 480 m2) trawl operations were conducted at different depths in the Kuroshio-Oyashio Transition Zone during 20–22 May 1995. While Japanese sardine Sardinops melanostictus and Japanese anchovy Engraulis japonicus were concentrated in the upper 20 m, mackerels Scomber spp. were collected uniformly in the upper 80 m layer. Myctophid fishes Ceratoscopelus warmingii, Diaphus kuroshio, Diogenichthys atlanticus, Myctophum asperum, Notoscopelus spp. mostly N. resplendens, and Symbolophorus californiensis, a gempylid Nealotus tripes, a microstomatid Lipolagus ochotensis and a phosichthyid Vinciguerria nimbaria were dominant components of mesopelagic fishes that ascended to the upper 100 m layer at night, where these mesopelagic fishes concentrated at depths of 20–80 m. In the upper 20 m layer, Japanese anchovy comprised 60% of the total wet weight of all fishes followed by D. atlanticus (3%). C. warmingii (2%) and S. californiensis (2%). Juvenile myctophids were dominant in the upper 20 m layer compared to deeper layers.

Age and growth of lanternfishes, Symbolophorus californiensis and Ceratoscopelus warmingii (Myctophidae), in the Kuroshio–Oyashio Transition Zone

To estimate the age and growth of dominant lanternfishes in the Kuroshio–Oyashio Transition Zone, we examined the sagittal otolith microstructure of Symbolophorus californiensis (n = 30) and Ceratoscopelus warmingii (n = 93) collected from the western North Pacific during 1997–2003. Age of S. californiensis ranged from 81 to 541 days corresponding to postmetamorphosis stage (juveniles and adults), and the von Bertalanffy model was fitted: Lt = 128[1 − exp{−0.003(t − 1.52)}], where L is the standard length (mm) and t is age in days. Age of C. warmingii ranged from 6 to 416 days, and growth before metamorphosis was linear (Lt = 0.346t + 1.51), and the von Bertalanffy model was fitted to the postmetamorphosis stage: Lt = 80.8 [1 − exp{−0.00769(t − 34.4)}]. Growth of these two lanternfishes was faster than that of other lanternfishes in previous studies but considerably slower than that of Japanese sardine (Sardinops melanostictus) and anchovy (Engraulis japonicus) distributed in the Kuroshio–Oyashio Transition Zone. Temperature and prey availability are discussed in relation to this difference in growth rate.