Dam construction has serious consequences for anadromous fishes. We examined the effects of migration barriers formed following dam construction on the migratory behavior of white-spotted char (Salvelinus leucomaenis) by comparing migrants in accessible below-dam river sections with migrants in inaccessible above-dam river sections. The frequency of smolts (i.e., potential migrant) was higher for the below-dam sections than for the above-dam sections, and in contrast, the frequency of residents was higher for the above-dam sections. Above-dam sections had lower fry (age 0+) densities and consequently had higher growth rates compared with below-dam sections. A transplant experiment revealed that the majority of the below-dam fish adopted a resident strategy, as well as above-dam fish, when both had experienced the above-dam environment. We conclude that high growth as a result of low density promotes residency in the above-dam sections.
Inter-decadal and geographic variations in the diets of Steller sea lion, Eumetopias jubatus, were examined based on the contents of 408 stomachs collected from coastal areas around Hokkaido Island during the periods 1994-1998 and 2005-2012
There is a need to establish a method of determining age and to investigate the relationship between the age and body size of the Northern Hokkaido stock of the Arabesque greenling Pleurogrammus azonus. Therefore, we examined the method of age validation by using otoliths, and estimated the relationship between age and size. A mass-processing method was used to section the otoliths. The annual growth of otoliths was veriˆed using edge-type analysis. The age of individualˆsh could be accurately validated by counting the number of outer edges of the translucent zones. Because of disagreement between the annual growth of otoliths and the formation of checks, the number of checks was considered unsuitable for age validation of the stock. Logistic growth models, which indicated diŠerential asymptotic length by sex, were estimated as the age size relationship of the stock.The growth of the Arabesque greenling was rapid up to 2 years of age, then slowed. We conclude that age validation is necessary for the stock because it is impossible to predict the age of theˆsh on the basis of size after 2 years of age.
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