Successive use of different habitats during the early life stages of Pacific herring <Emphasis Type="Italic">Clupea pallasii</Emphasis> in Akkeshi waters on the east coast of Hokkaido

Distributions of eggs, larvae and juveniles of Pacific herring Clupea pallasii were surveyed in Lake Akkeshi and the connecting Akkeshi Bay on the Pacific coast of eastern Hokkaido. Eggs were found attached to seagrasses and seaweeds in the densely vegetated eastern inner lake. Larvae (7.1–34.9 mm total length) were distributed in the less densely vegetated inner lake during April and June. Juveniles (35.0–89.6 mm) were collected in the central and western parts of the lake. The sites containing juveniles were less densely vegetated with water temperatures lower than 20 °C from June to August. When the water temperature of the entire lake rose to 20 °C in late summer, juveniles appeared to move from the lake to the bottom layer of Akkeshi Bay, which has lower temperatures. Thus, in Akkeshi waters, C. pallasii successively used different habitats during its egg, larval and juvenile stages. A comparison of the current limited distribution of eggs and larvae with the distribution over the entire lake and bay areas in the 1950s and 1960s (periods of large catch size) indicates that the spawning grounds and larval habitats of C. pallasii have contracted to the lake area due to low spawning stock biomass in recent years.     

Impact of wind direction on diurnal and seasonal changes in wind profiles

We explored the relationship between directional variation (changes in direction from a reference point) in vegetation and wind profiles, and propose an empirical wind profile model that may reproduce the wind profile within the canopy (such as secondary wind maximum) and reduce calculation loads. Based on the results of our observations in secondary broad-leaved forest, we clarified the variation in secondary wind maximum and aerodynamic parameters in wind direction, and assessed the influence of forest structural heterogeneity on the wind profile. Wind blew from specific directions depending on the time of day and season, and secondary wind maxima were observed in particular wind directions. Outlier estimations of aerodynamic parameters were determined for wind directions of 45°, 120–210°, and 300°, and these did not show a logarithmic distribution. Our proposed model reproduced the wind profile within and above the canopy, closely resembling K-theory and closure models, and reduced the required number of calculations and observations. The influence of forest structural heterogeneity was greatest in the upper part of the canopy (9.14 m), and reproducibility of the wind profile was improved by 0.05 m/s (3.4% on average) by changing the forest structural parameters of the model according to the wind direction. It was clear that forest structural heterogeneity did not cause critical errors in estimation of the wind profile, even at our study site, which had complex forest structure.