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.
Chemistry of otoliths from juvenile menhaden Brevoortia patronus: evaluating strontium, strontium:calcium and strontium isotope ratios as environmental indicators
Laboratory studies were conducted, to establish the utility of otolith chemistry for tracing gulf menhaden Brevoortia patronus environmental histories Menhaden larvae were hatched from eggs and reared to juveniles under constant conditions at 3 temperatures (18, 22, 26°C) and 3 salinities (20. 26, 33.4). Whole otoliths from exper~mental fish along with their rearing waters were analyzed by ICPMS (inductively coupled plasma mass spectrometry) and TIMS (thermal ionization mass spcctrometry) to determine thc effects of temperature and salinlty on Sr concentration, Sr/Ca and "Sr/"'Sr. A comparison of clcmental composition by otolith type revealed significantly lower Sr concentrations and lower Sr/Ca ratios in the asteriscus versus the sagitta and lapillus. X-ray diffraction analyses for each otolith type determined that lnenhaden sdglttae and lapllli are aragonite whlle their asterisci are vaterite. This suggests the type of calcium carbonate matrix deposited can affect the concentrations of trace elements incorporated into otoliths In laboratory reared menhaden no significant relationships between Sr concentration or Sr/Ca ratios and temperature, salinity or menhaden growth rate were detected (ANOVA, p = 0.05). Wc found no indication that R7Sr/86Sr ratios of menhaden otoliths were affected by water temperature. H'Sr/flh~r did reflect the salinity of the rearing water; however, the relationship between Sr isotope ratios and salinity limits the utility of Sr isotope ratios a s a precise indicator of salinity to low salinity environments (<20) or over wide ranges of salinity. A comparison between Sr isotope ratios of menhaden otoliths and menhaden vertebrae, along with an analysis of a vertebra from a reproductive adult bay anchovy Anchoa mitchilli, showed there was no significant difference between otolith and vertebra R7Sr/R6Sr ratlos, Indicating that other bony structures might be suitable for strontium isotope analyses in sinall indiv~dual fish.