Dam construction has serious consequences, and one of the most serious concerns is the fragmentation of riverine ecosystems. We reviewed the influence of habitat fragmentation on white-spotted charr Salvelinus leucomaenis populations. First, habitat fragmentation by damming has serious consequences in terms of alternative life-history strategies. Most fish in dammed-off areas do not migrate to the sea and instead become resident forms. This loss of the anadromous form negatively affects populations through decreased spawning biomass. In addition, the smaller population sizes in dammed-off habitats can negatively affect population dynamics through demographic, environmental, and genetic stochasticity. Therefore, the population viability is reduced in small, dammed-off habitats. White-spotted charr populations also likely experience different selection pressures after damming. Many of these effects of habitat fragmentation due to damming are not immediate but rather occur gradually over several generations. Because most Japanese dams were constructed after 1970, some effects of damming may not yet be obvious.

In the last quarter of the 20th century, the size at maturity of many North Pacific salmon (Oncorhynchus spp.) populations decreased. During this same period, the age at maturity increased, implying that the growth rate of Pacific salmon decreased, probably owing to environmental changes. To elucidate these trends, we identified the rule of age and size at maturity of Japanese chum salmon (Oncorhynchus keta), which was that slow-growing salmon initiated maturation at an older age and smaller size than did fast-growing salmon. We then simulated the potential modification of age and size at maturity in response to changing growth rate using a size-structured model with age-and sizespecific maturation rates. This showed that reducing the growth rate without assuming a genetic change was sufficient for realistic modeling of recent changes. In addition, the observed rule of age and size at maturity was consistent with the optimal age and size at maturity in terms of maximizing the fitness. Our results attributed the recent trends in chum salmon's increasing age and decreasing size at maturity to an adaptive phenotypic response to a reduced growth rate.Résumé : Durant le dernier quart du 20 e siècle, la taille à la maturité a décliné chez plusieurs populations de saumons (Oncorhynchus spp.) du Pacifique Nord. Durant la même période, l'âge à la maturité a augmenté, ce qui indique que le taux de croissance des saumons du Pacifique a diminué, probablement à cause des changements environnementaux. Afin d'élucider ces tendances, nous avons identifié la règle de la taille et de l'âge à la maturité du saumon kéta (Oncorhynchus keta) du Japon, qui veut que les saumons à croissance lente commencent leur maturation à un âge plus avancé et à une taille plus petite que les saumons à croissance rapide. Nous avons ensuite simulé une modification potentielle de l'âge et de la taille à la maturité en réaction à des changements de taux de croissance, à l'aide d'un modèle structuré en fonction de la taille possédant des taux de maturation spécifiques à l'âge et à la taille. Cette simulation démontre qu'une réduction du taux de croissance, sans présupposition de changement génétique, suffit pour permettre de modéliser de façon réaliste les changements récents. De plus, la règle de l'âge et de la taille à la maturité observée est compatible avec l'âge et la taille à la maturité optimaux de façon à maximiser le fitness. Nos résultats expliquent les tendances d'augmentation de l'âge et de diminution de la taille à la maturité chez le saumon kéta par une réaction phénotypique à une réduction du taux de croissance.[Traduit par la Rédaction] Morita et al. 2759

To determine whether the brown root rot disease caused by Phellinus noxius is present in the Amami islands, which are situated near Okinawa, we conducted six field surveys from 1999 to 2005. The brown root rot disease was found in 22 tree species in 17 plant families at 25 different sites in all the islands surveyed. Sixteen of these species were newly recorded as host plants of P. noxius. The disease was more common in the low elevation plains and on hills less than 100 m above sea level than in mountainous areas. This is the first report of the brown root rot disease caused by P. noxius in the Amami Islands, Japan, and Ohshima Island is currently the northern-most distribution point of the disease in the northern hemisphere.

Individual growth and maturation histories, age, and size at maturity of resident white-spotted charr Salvelinus leucomaenis were examined in a tag-recapture study in a natural river over 3 years. Slow-growing fish reached sexual maturity not only at an older age, but also at a smaller size than fast-growing fish, although females had a larger threshold size at maturity than males at each age. It is suggested that these patterns result from adaptive phenotypic plasticity that depends on individual growth conditions.

Hatchery programs involving the mass release of artificially propagated fishes have been implemented worldwide. However, few studies have assessed whether hatchery programs actually increase the net population growth of the target species after accounting for the effects of density dependence and climatic variation. We examined the combined effects of density dependence, climatic variation, and hatchery release on the population dynamics of Japanese pink salmon (Oncorhynchus gorbuscha) from 1969 to 2003. The population trends were more closely linked to climatic factors than to the intensity of the hatchery programs. The estimated contributions of hatchery-released fry to catches during the past decade are small. We concluded that the recent catch increases of Japanese pink salmon could be largely explained by climate change, with increased hatchery releases having little effect.