Tian, Y., Uchikawa, K., Ueda, Y., and Cheng, J. Comparison of fluctuations in fish communities and trophic structures of ecosystems from three currents around Japan: synchronies and differences. – ICES Journal of Marine Science, 71: . Features of three marine ecosystems affected by the Tsushima (TWC), Kuroshio (KC), and Oyashio (OC) currents were analysed based on fishery, oceanographic, and climate datasets during 1955–2010. Principal component (PC) analysis for catches of 25 indicator species showed evident decadal variation patterns with a step change in the first principal component (PC1) in the late 1980s, indicating synchronies in the dominant variation mode across the ecosystems. Step changes were also detected in the mid-1970s in PC2 and PC3 in OC, and around 1970 in PCs in KC and TWC. These indicate that the most marked change across the ecosystems occurred in the late 1980s, corresponding to the late 1980s climate regime shift, but OC also responded strongly to the mid-1970s regime shift, indicating different responses to regime shifts. The generalized additive model showed the PCs associated largely with water temperature in each region as well as climate indices, indicating the importance of regional oceanographic conditions. Ecosystem indicators such as the mean trophic level showed similarities between TWC and KC but differences with OC, indicating that trophic structures in TWC and KC were largely dependent on the mid-trophic (small pelagic species) level, while on demersal species in OC.
We compared the diet of Ommastrephes bartramii paralarvae with morphological changes in their beaks and proboscis (fused tentacles). The paralarvae were collected north of the Hawaiian Islands during 2001 and 2002 and ranged in mantle length (ML) from 1.1 to 13.2 mm. They fed on crustaceans, including copepods (copepodite stage) and amphipods. The rostral tips of upper and lower beaks began to protrude anteriorly at around 3-4 mm ML, and the smallest paralarva with identifiable prey in its digestive tract was 4.2 mm ML, which suggests that the paralarvae can masticate prey soon after the beaks protrude. The proboscis separated into two tentacles at 9.3-13.2 mm ML, but the newly formed tentacles were weakly developed even in the largest specimen, suggesting that tentacles do not operate functionally and that the arms are used to capture prey.
ABSTRACT:The diet of Notoscopelus japonicus, one of the dominant mesopelagic fishes in the transitional waters of the western North Pacific, was examined in 106 specimens collected over the continental slope off the Pacific coast of northern Japan during April and October 1996. The prey comprised mainly crustaceans, such as copepods, ostracods, euphausiids and amphipods. Euphausia pacifica was the dominant prey, representing 83.1 % by number and 72.4% by wet weight of the total diet. Between April and October, there was no shift in prey species consumed, but prey size decreased significantly and prey number per fish stomach increased in October. These results indi-. catethat, in October, N. japonicus consumed larger numbers of smaller E. pacifica, rather than shifting to other prey taxa. The pronounced importance of E. pacifica in the diet was ascribed to its co-occurrence with N. japonicus at night in the surface layer and during the daytime in the nearbottom layer.
: The feeding habits of Lampanyctus jordani, an abundant mesopelagic fish in the subarctic North Pacific, was examined based on the stomach contents of 721 specimens collected over the continental slope off the Tohoku area, Pacific coast of northern Japan during April and October from 1996 to 1998. The prey items comprised mainly crustaceans such as copepods, amphipods, euphausiids and decapods. Euphausiids were the most important items in the diet both during April and October. During April, when the annual maximum of zooplankton biomass occurred and the Oyashio Intrusion Current prevailed, L. jordani fed intensively and consumed a high proportion of Euphausia pacifica. These seasonal variations also influenced the feeding intensity and dietary diversity. Feeding intensity, measured by the stomach contents index, was higher during April than October, reflecting the higher biomass of zooplankton in the Tohoku area during spring. The dietary diversity of L. jordani was lower during April than October, indicating that L. jordani shifted to a wider variety of prey when the availability of E. pacifica was limited.
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