Flexible seaward migration of Dolly Varden Salvelinus malma in the Shiretoko Peninsula, Hokkaido, Japan
The migratory history of Dolly Varden Salvelinus malma was investigated in 30 streams in the Shiretoko Peninsula, Hokkaido, Japan, which is in the southern part of their distribution. Captured Dolly Varden were classified into two categories by their body coloration: silvery fish were thought to be an anadromous form, and non-silvery fish a fluvial form that remains in freshwater throughout its life. Forty-seven of 1,739 Dolly Varden collected in the spring and ten of 2,126 Dolly Varden collected in the autumn were silvery fish. Twenty silvery fish and 120 non-silvery fish were examined by analysis of otolith Sr:Ca ratio. Three silvery fish from autumn and 15 non-silvery fish had migrated to salt water or brackish water. The other specimens of silvery fish were regarded as smolt or pre-smolt before seaward migration. The present study suggests that Dolly Varden in the Shiretoko Peninsula have a flexible migratory history, where some of the non-silvery fish utilize marine environments while some individuals follow an anadromous life history.
Potential fragmentation and loss of thermal habitats for charrs in the Japanese archipelago due to climatic warming
1. The upper thermal limits of the present distributions of two charr species, Dolly Varden, Salvelinus malma, and white-spotted charr, S. leucomaenis, in streams of the Japanese archipelago were examined using groundwater temperature as an index of thermal condition. The lower limits of the altitudinal distributions of Dolly Varden and white-spotted charr were delineated, respectively, by 8 and 16 °C groundwater isotherms. 
 
 
 
2. The potential impact of future climatic warming on the geographical distribution, habitat extent and population fragmentation of each species was predicted at both the full archipelago and individual catchment levels. 
 
 
 
3. For Dolly Varden, analysis at the full archipelago level indicated a loss of 27.6, 67.2, 79.6 and 89.6% of the current geographical range, respectively, for a 1, 2, 3 and 4 °C increase in mean annual air temperature. The present distribution area of white-spotted charr would likewise reduce by 4.1, 20.5, 33.8 and 45.6%, respectively. 
 
 
 
4. Based on the analyses of three individual catchments, one for Dolly Varden and two for white-spotted charr, the lower habitat boundaries for the two charr species could be expected to rise increasingly to higher elevations in each catchment as warming proceeded. As a consequence, there would be large reductions in mean habitat area, with increasing habitat fragmentation followed by localized extinctions of the two species.
Strontium incorporation into calcified structures: separating the effects of ambient water concentration and exposure time
Chemical elements within calcified structures of organisms such as fish, corals, bivalves, gastropods and foraminiferal shells can provide a record of the environmental characteristics at the time of calcification. To predict accurately the environmental characteristics at the time of calcifica- tion, it is important to understand the influence of exposure time on elemental incorporation. We examined the effect of enhanced ambient strontium:calcium (Sr:Ca) (2 × and 4 × ambient concentra- tions) and different periods of exposure (2, 4, 8, 16 and 32 d) on Sr:Ca uptake and incorporation into fish otoliths of the black bream Acanthopagrus butcheri (family: Sparidae). Sr:Ca ratios (hereafter referred to as concentrations) in bream otoliths increased with increasing ambient concentrations, with the amount of Sr:Ca incorporated into otoliths being positively affected by the period of expo- sure. Saturation of Sr:Ca in otoliths occurred after 20 d of exposure. Importantly, by measuring mul- tiple variables of elemental uptake and incorporation, the relative effect of enhanced concentration and exposure time can be separated, which to date has not been possible. This research will allow for greater accuracy when interpreting environmental histories of fish.