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.
Relationship of otolith strontium-to-calcium ratios and salinity: experimental validation for juvenile salmonids
Analysis of otolith strontium (Sr) or strontium-to-calcium (Sr:Ca) ratios provides a powerful tool to reconstruct the chronology of migration among salinity environments for diadromous salmonids. Although use of this method has been validated by examination of known individuals and translocation experiments, it has never been validated under controlled experimental conditions. In this study, incorporation of otolith Sr was tested across a range of salinities and resulting levels of ambient Sr and Ca concentrations in juvenile chinook salmon (Oncorhynchus tshawytscha), coho salmon (Oncorhynchus kisutch), sockeye salmon (Oncorhynchus nerka), rainbow trout (Onco- rhynchus mykiss), and Arctic char (Salvelinus alpinus). Experimental water was mixed, using stream water and seawa- ter as end members, to create experimental salinities of 0.1, 6.3, 12.7, 18.6, 25.5, and 33.0 psu. Otolith Sr and Sr:Ca ratios were significantly related to salinity for all species (r 2 range: 0.80-0.91) but provide only enough predictive reso- lution to discriminate among fresh water, brackish water, and saltwater residency. These results validate the use of otolith Sr:Ca ratios to broadly discriminate salinity histories encountered by salmonids but highlight the need for fur- ther research concerning the influence of osmoregulation and physiological changes associated with smolting on otolith microchemistry. Resume : L'analyse des concentrations de strontium (Sr) et des rapports strontium:calcium (Sr:Ca) dans les otolithes est un outil puissant pour la reconstitution de la chronologie de la migration dans des environnements de salinite diffe- rente chez les samonides diadromes. Bien que la methode ait ete validee par l'examen d'individus connus et des expe- riences de translocation, elle ne l'a jamais ete dans des conditions experimentales controlees. La presente etude verifie l'incorporation du Sr dans les otolithes sur une gamme de salinites et mesure les concentrations ambiantes de Sr et de Ca qui en resultent chez de jeunes saumons quinnat (Oncorhynchus tshawytscha), saumons coho (Oncorhynchus ki- sutch), saumons rouges (Oncorhynchus nerka), truites arc-en-ciel (Oncorhynchus mykiss) et ombles chevaliers (Salveli- nus alpinus). L'eau utilisee dans les experience est un melange d'eau de ruisseau et d'eau de mer de maniere a obtenir des salinites de 0,1, 6,3, 12,7, 18,6, 25,5 et 33,0 ups. Chez toutes les especes, il y a une relation significative entre la concentration de strontium et le rapport Sr:Ca des otolithes d'une part et la salinite d'autre part (etendue de r 2 : 0,80- 0,91); cependant, la relation n'est suffisamment predictive que pour permettre de discriminer entre les sejours en eau douce, en eau saumâtre et en eau salee. Ces resultats permettent de valider l'utilisation des rapports Sr:Ca pour distin- guer grossierement les sejours passes des saumons dans des milieux de differentes salinites; ils demontrent cependant l'importance de recherches futures sur l'influence de l'osmoregulation et des changements physiologiques associes a la transformation en saumoneau sur la microchimie des otolithes. (Traduit par la Redaction) Zimmerman 97
Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido
Nomoto K, Omiya H, Sugimoto T, Akiba K, Edo K, Higashi S. Potential negative impacts of introduced rainbow trout on endangered Sakhalin taimen through redd disturbance in an agricultural stream, eastern Hokkaido. Ecology of Freshwater Fish 2010: 19: 116–126. © 2009 John Wiley & Sons A/S 
 
 
 
Abstract –  Sakhalin taimen (Hucho perryi) populations have decreased in Hokkaido, northernmost Japan, primarily because of overexploitation and habitat degradation. Here we document another threat to this species, that of spawning redd superimposition by artificially introduced rainbow trout (Oncorhynchus mykiss). Sakhalin taimen and rainbow trout are the only spring-spawning salmonid species in Hokkaido. In 2006–2008, spawning activities of both these species were observed in a Hokkaido stream, and it was determined that their spawning periods overlapped during mid-late April. They also spawned at similar water velocities, depths and substrate compositions. Although female Sakhalin taimen were larger than female rainbow trout, their egg burial depths were nearly identical. During the observation period, rainbow trout redds were approximately five times more abundant than Sakhalin taimen redds, and about 30% of the observed Sakhalin taimen redds were superimposed by rainbow trout redds. The high degree of spatial and temporal overlap in spawning, the similar egg burial depths of both species, and the high proportion of superimposed redds suggest that the introduced rainbow trout impact the endangered Sakhalin taimen in Hokkaido, and possibly, in other areas where the two species occur together.