Eight temperature‐recording data storage tags were recovered from three salmonids in Alaska (pink and coho salmon and steelhead trout) and five chum salmon in Japan after 21–117 days, containing the first long‐term records of ambient temperature from Pacific salmonids migrating at sea. Temperature data imply diel patterns of descents to deeper, cooler water and ascents to the surface. Fish were found at higher average temperatures at night, with narrower temperature ranges and fewer descents than during the day. Fish tagged in the Gulf of Alaska were at higher temperatures on average (10–12°C) than chum salmon tagged in the Bering Sea (8–10°C). Chum salmon were also found at a wider range of temperatures (−1–22°C vs 5–15°C). This is probably related both to the different oceanographic regions through which the fish migrated, as well as species differences in thermal range and vertical movements. Proportions of time that individual fish spent at different temperatures seemed to vary among oceanographic regions. Steelhead trout may descend to moderate depths (50 m) and not be limited to the top few metres, as had been believed. Japanese chum salmon may seek deep, cold waters as they encounter warm surface temperatures on their homeward migrations. Temperature data from all fish showed an initial period (4–21 days) of day and night temperatures near those of sea surface temperatures, suggesting a period of recuperation from tagging trauma. A period of tagging recuperation suggests that vertical movement data from short‐term ultrasonic telemetry studies may not represent normal behaviour of fish. The considerable diurnal and shorter‐term variation in ambient temperatures suggests that offshore ocean distribution may be linked more to prey distribution and foraging than to sea surface temperatures.

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Ichthyobodo necator is a parasitic flagellate that attacks fishes, causing disease problems in freshwater worldwide. Findings of similar flagellates in strictly marine fishes have indicated that ichthyobodiosis may be caused by more than 1 flagellate species. We obtained partial small subunit rDNA (ssu rDNA) sequences of 14 Ichthyobodo isolates originating from fishes in Norway, Japan, Singapore, South Africa and Brazil, and identified 8 strains or species, including 2 species infecting cultured salmon in Norway. An Ichthyobodo species isolated from the skin of Atlantic salmon parr in freshwater is suggested to represent I. necator sensu stricto, while another species, showing particular affinity for the gills, infects salmon in both fresh-and seawater. Atlantic cod is infected with a marine Ichthyobodo species unrelated to those infecting salmonids; 2 cyprinids originating from different parts of the world had related Ichthyobodo strains/species, and 2 isolates from unrelated North and South American fishes were also closely related. The phylogenetic relationships of the Ichthyobodo isolates is described, and the implications of the molecular findings on past and future morphological studies of Ichthyobodo spp. are discussed.

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A three-agency program was initiated in 1989 to develop a new multilocus genetic baseline for chum salmon (Oncorhynchus keta) in Japan and Russia for use in stock identification; allele frequencies at 77 allozyme loci are reported in 38 samples covering most of its north–south limits of distribution in Asia. In a 62-locus data set for 17 Japanese and 12 Russian samples, average heterozygosity ranged from 0.066 to 0.087 (mean 0.079) and the average number of P0.95 and P0.99 loci was 14 and 26, respectively. Tests of year-to-year variation in allele frequencies were not significant at five of six locations. For the P0.95 loci, FST values ranged from 0.007 (sMDH-B1*) to 0.154 (mAAT-2*) and averaged 0.038. A clear distinction between Russian and Japanese samples was observed at Nei's D = 0.006, and genetic differentiation generally followed a regional pattern within each country. Principal component analysis of the P0.95 loci revealed a large difference between Japanese and Russian samples. Four loci (sAAT-1,2*, mAAT-2*, LDH-A1*, and PEPLT*) had high loadings on the first two principal components. Analyses of a simulated fishery with 200 fish revealed a high degree of precision in estimating contributions to seven population groups and to country of origin.

We examined the nucleotide sequences of 500 bp variable portion from the 5' end of mitochondrial (mt) DNA control region in about 500 individuals from 12 populations that were captured in 11 rivers, six in Hokkaido and five in Honshu, Japan. Comparison of the sequences showed 10 variable sites, defining a total of 12 haplotypes in the examined individuals. All the 12 haplotypes occurred in seven Hokkaido populations, whereas only six haplotypes were found in the five Honshu populations. Among these haplotypes, two were common in all the Hokkaido and Honshu populations. The AMOVA analysis inferred a genetic differentiation among three geographic regions, i.e. Hokkaido, Pacific Ocean coast in Honshu, and Japan Sea coast in Honshu. Haplotype diversity was higher in the populations of Hokkaido than those of Honshu, indicating a greater genetic variation in the Hokkaido than the Honshu populations. The estimates of pairwise population F ST suggested that the regional differentiation was mostly ascribed to the divergence between populations in Hokkaido and the Pacific coast in Honshu.

Variation at 14 microsatellite loci was surveyed in 26 chum salmon Oncorhynchus keta populations from Japan, one population from West Kamchatka and three populations from North America to determine population structure. Microsatellites were then applied to estimate stock composition of chum salmon in mixed-stock fisheries. The genetic differentiation index (Fst) over all populations and loci was 0.031, with individual locus values ranging from 0.010 to 0.081. Seven regional populations were observed in Japanese chum salmon, with late-run populations from the Pacific Coast of Honshu the most distinct. Japanese populations displayed greater genetic diversity than did those in North America. Transplantation history in some Japanese river populations influenced their present genetic characteristics. Analysis of simulated mixtures from fishery sampling suggested that accurate and precise regional estimates of stock composition should be produced when the microsatellites were used to estimate stock compositions. Stock compositions for a 2005 sample of maturing, migrating chum salmon off the north-west coast of Hokkaido near the border of the Sea of Japan and the Sea of Okhotsk indicated that this region may be a migration corridor for Hokkaido populations from the Sea of Japan coast. Microsatellites have the ability to provide fine-scale resolution of stock composition in Japanese coastal fisheries.

The swimming behavior of the chum salmon Oncorhynchus keta was studied for 53 d of its 67 d oceanic migration from the central Bering Sea to the Japanese coast. We provide the first data on swimming speeds by a homing salmon, recorded at 5 s intervals by a fish-borne time-speed, depth, and temperature logger. Swimming speed rarely exceeded 1.0 m s^[-1], and horizontal swimming speed was 36.4 ± 15.2 km d^[-1]. Cumulative horizontal swimming distance was approximately 2500 km, equivalent to 90% of the minimum distance between the release and recovery sites (2760 km). Swimming depth and speed peaked around dawn and dusk, and there was a smaller peak around midnight. The fish showed sequential up-and-down movement near the thermocline during daytime. Diurnal patterns of movement suggest that homing chum salmon spend a considerable time foraging, and the strategy is different between daytime and nighttime. Our findings indicate that over large distances of ocean, a homing salmon maintains a strong homeward orientation, but that passive transport by favorable water currents may help the migration