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.
Migration history of Sakhalin taimen Hucho perryi captured in the Sea of Okhotsk, northern Japan, using otolith Sr:Ca ratios
Sakhalin taimen Hucho perryi populations have decreased drastically to near extinction. It is urgent to establish an effective conservation strategy based on an understanding of the characteristics of migration and habitat use of this species. We examined the migration history of anadromous Sakhalin taimen captured off the Sarufutsu coast, northern Hokkaido, Japan, using otolith Sr:Ca ratios and also examined the relationship between their otolith Sr:Ca ratios during freshwater and seawater residence in a rearing experiment. Otolith Sr:Ca ratios of some fish from the Sarufutsu coast showed freshwater levels (0.5–4.0 × 10−3) near the core, which thereafter increased to brackish water levels (4.0–6.0 × 10−3), and then to seawater levels (6.0–10.0 × 10−3) in the outermost regions. Those findings indicate that specimens from the Sarufutsu coast migrated to the brackish water region or the sea and spent most of their lives there. The anadromous migration pattern including the timing of downstream migration seems to be flexible among individuals in the species. They migrate between freshwater and seawater or brackish water several times during their lives, showing extensive habitat use. It is essential to secure the continuity among the freshwater, brackish water, and seawater areas for their effective conservation.
New records of Grania (Clitellata, Enchytraeidae) in the Northeast Atlantic (from Tromsø to the Canary Islands), with descriptions of seven new species
Previous northeast Atlantic records of Grania have been mainly from Germany, southern Scandinavia, and the Atlantic shores of France, Spain and Ireland. They were referred to eight species, with one, G. atlantica, reported from the continental slope. We have examined various unpublished collections from sources spanning from the Canary Islands to the Norwegian Arctic. Apart from new information on morphology, taxonomy, and distribution of known species, we describe seven new taxa (G. canaria, G. fortunata, G. mauretanica, G. aquitana, G. vikinga, G. torosa, and G. papillinasus). The collection of G. papillinasus from 2630-2885 m represents a new depth record for Enchytraeidae. Twenty-five of the now 57 Grania species occur in the North Atlantic. The North Atlantic drift moderates sea temperatures along the northeast Atlantic coasts, probably facilitating the wide latitudinal range of some taxa, as well as actual dispersal within the region. A "chaetal index" (chaetal length : chaetal foot length) is proposed to differentiate L-shaped chaetae at the species level. Complex relationships within the "type 6 group" of Grania suggest that groupings established using certain combinations of penial, chaetal and spermathecal patterns may not be monophyletic. For a better phylogenetic resolution, additional morphological details of these and other characters are needed.