Investigation of inter-annual variation in the feeding habits of Japanese sardine (Sardinops melanostictus) and mackerels (Scomber spp.) in the Western North Pacific based on bulk and amino acid stable isotopes

Inter-annual variation in the feeding habits and food sources of Japanese sardine and mackerel at age-0 and age-1+ caught in the Kuroshio-Oyashio transition zone of the Western North Pacific were investigated based on analyses of bulk stable isotopes (δ13C, δ15N) and amino acid nitrogen isotopes (δ15NAA). Differences in δ13C and δ15N between Japanese sardine and mackerel were small for age-0, and inter-annual variation trends were similar, suggesting they depend on similar food sources in the same food web at this age. In contrast, inter-annual variation in δ13C and δ15N were significantly different between both species at age-1+, and both δ15N of phenylalanine (δ15NPhe: an indicator of nitrogen source) and trophic position estimated from δ15NAA (TPAA) were higher in mackerel, suggesting that the two species depend on distinct food webs as they age. Inter-annual variations in δ15NPhe were considered to have different causes for the two species; differences in food web structure due to the degree of southward intrusion of the Oyashio Current for Japanese sardine, compared to a shift in migration area and depth for mackerel. Furthermore, competition for food due to the recent increases in the population densities of both fishes appeared to be reflected in increased TPAA of mackerel. Although they are caught in the same region, the mechanism of variation in food sources differs because of differences in migration area, depth, and feeding habits. Differences in the feeding habits of Japanese sardine and mackerel may affect trophic status and spawning characteristics, potentially leading to different shifts in stock abundances

A lower trophic ecosystem model including iron effects in the Okhotsk Sea

We applied a three-dimensional ecosystem-physical coupled model including iron the effect to the Okhotsk Sea. In order to clarify the sources of iron, four dissolved iron compartments, based on the sources of supply, were added to Kawamiya et al.’s(1995) model (KKYS) to create our ecosystem model (KKYS-Fe). We hypothesized that four processes supply iron to sea water: atmospheric loadings from Northeastern Asia, input from the Amur River, dissolution from sediments and regeneration by zooplankton and bacteria. We simulated 1year, from 1 January, 2001 to 31 December, 2001, using both KKYS-Fe and KKYS. KKYS could not reproduce the surface nitrate distribution after the spring bloom, whereas KKYS-Fe agreed well with observations in the northwestern Pacific because it includes iron limitation of phytoplankton growth. During the spring bloom, the main source of iron at the sea surface is from the atmosphere. The contribution of riverine iron to the total iron utilized for primary production is small in the Okhotsk Sea. Atmospheric deposition, the iron flux from sediment and regeneration of iron in the water column play important roles in maintaining high primary production in the Okhotsk Sea

Characteristics of suspended sediment material transport in the Ishikari Bay in snowmelt season

The present paper aims at studies of the suspended sediment transport in inner Ishikari Bay in snowmelt season using a numerical approach and field observation data. The sediment transport and bottom boundary layer models are coupled into the Princeton Ocean Model to compute suspended sediment concentration in the system. The following findings have been deduced: (1) The suspended sediment transport in the study area in snowmelt season is dominated by the sediment discharge from the Ishikari River. The effect of sediment resuspension due to wave current interaction is limited to a very shallow area along the coast. (2) A comparison between observed and computed suspended sediment concentrations shows that the model can reproduce reasonably well the general features of the dynamics of suspended sediment transport in Ishikari Bay in snowmelt season. (3) The suspended sediment matter (SSM) from the Ishikari River is mainly transported northward. The vertical structure of SSM concentration displays a slow sinking of sediment matter supplied to the water column from the surface i.e. high sediment concentration is seen in surface layers and it gradually deceases in the lower layers. (4) After two months of simulation, net erosion occurs in a narrow area nearshore. The average erosion depth in this area is 0.16 mm. Net deposition locates in a wider area north of the inner bay. The average deposition depth in this area is 0.04 mm

Theoretical Analysis of Dependence of Nonlinear Effects in Mode-Locked Yb:YAG Lasers with a Highly Nonlinear Intra-Cavity Medium

Nonlinear ultrashort pulse propagation in a mode-locked Yb:YAG laser with a highly nonlinear intra-cavity medium is analyzed using a nonlinear Schrodinger equation. The output spectra are extended by the increased laser intensity, and spectral bandwidths wider than those of the gain medium are achieved. Moreover, pulse widths are shortened by increased laser intensity to considerably less than those of the gain medium. The simulation results qualitatively agree with the experimental results