Otolith radiocarbon signatures provide distinct migration history of walleye pollock around Hokkaido, Japan in the North-Western Pacific.

Trace elements and stable isotope ratios in otoliths have been used as proxies for the migration history of teleosts; however, their application in oceanic fishes remains limited. This study reports the first use of radiocarbons in otoliths to evaluate the horizontal migration histories of an oceanic fish species, the walleye pollock Gadus chalcogrammus. We conducted radiocarbon analyses of three stocks sourced from Hokkaido, Japan. The radiocarbon concentrations from the outermost portion of the otoliths from the Japanese Pacific, Northern Japan Sea (JS), and Southern Okhotsk Sea (OS) stocks were in general agreement with the seawater radiocarbon concentration of the sampling region, suggesting that pollock of all three stocks generally inhabited the within the sea region where each pollocks were sampled throughout their life cycle. However, the radiocarbon signals also provided some indications that some JS and OS stocks may be migrating between different sea regions. The proposed novel approach of reconstructing the individual migration history of marine fish using radiocarbon in otoliths may help examine fish migration with a higher temporal and spatial resolution that could not be achieved by trace elements and stable isotope ratios.

Bathyraja (Arctoraja) sexoculata sp. nov., a new softnose skate (Rajiformes: Arhynchobatidae) from Simushir Island, Kuril Islands (western North Pacific), with special reference to geographic variations in Bathyraja (Arctoraja) smirnovi.

A new species of softnose skate (Arhynchobatidae), Bathyraja sexoculata Misawa, Orlov, Orlova, Gordeev and Ishihara is described on the basis of five specimens collected from off the east coast of Simushir Island, Kuril Islands, located in the western North Pacific. The specimens conformed to the genus Bathyraja by having the anteriormost pectoral-fin skeleton almost reaching the snout tip, and a slender unsegmented rostral cartilage. Within Bathyraja, the new species belongs to the subgenus Arctoraja (currently with four valid species) due to the relatively short tail (79-86% of disc width), high count of predorsal caudal vertebrae (more than 86), and large strong nuchal and scapular thorns. It is most similar to Bathyraja (Arctoraja) smirnovi, distributed in the Seas of Japan and Okhotsk, in having tail thorns not extending to the nuchal area, median thorns discontinuous from the nape to the tail, and no mid-dorsal thorns. However, B. sexoculata can be distinguished from B. smirnovi by the following characters: three pairs of white blotches on the dorsal disc surface (vs. blotches absent, or a pair of white or dark blotches in B. smirnovi), dark blotch around cloaca, dark bands along mid ventral line of tail (vs. dark blotch and band usually absent ventral disc surface in B. smirnovi), 86-93 predorsal caudal vertebrae (vs. 80-87 in B. smirnovi), and a unique mitochondrial DNA cytochrome c oxidase subunit I sequence. Proportional measurements, including disc width, disc length, head length, preoral length, prenarial length, internarial distance, eye diameter, and tail length, also differ between the two species. For the referential purpose, geographical variations of B. smirnovi distributed in the Seas of Japan and Okhotsk are analyzed and clarified based on morphological and genetic data. Significant morphological and genetic differences were found between local populations in the Seas of Japan and Okhotsk.

Inbreeding between Deep-Sea Snailfishes Careproctus pellucidus and Careproctus rastrinus in the Northwestern Pacific Ocean.

Genetic deviation between two deep-sea snailfishes, Careproctus pellucidus from the Pacific Ocean and Careproctus rastrinus from the Okhotsk Sea, of the Careproctus rastrinus species complex was analyzed, based on the nucleotide sequences of the mitochondrial cytochrome b (Cytb) gene. Our sampling revealed the occurrence of individuals with C. rastrinus-type Cytb genes off northeastern Japan, in the northwestern Pacific. Most of these individuals were collected from an area off Miyagi Prefecture, while few individuals were collected from areas to its north (off Iwate Prefecture) and south (off Fukushima and Ibaraki Prefectures). Phylogeographic analyses based on nucleotide sequences of the first intron region of the nuclear S7 ribosomal protein gene (S7) and 11 microsatellite loci indicated little genetic deviation between individuals with C. pellucidus-type and C. rastrinus-type Cytb genes in the area off Miyagi Prefecture. Significant genetic differences between the Pacific Ocean and the Okhotsk Sea populations may be attributed to unidirectional migration due to a greater current from the latter to the former. In addition, peritoneum and stomach colors of 10 and 17 specimens collected from the Pacific Ocean and the Okhotsk Sea, respectively, were evaluated quantitatively. The colors were significantly different for the two populations; however, they appeared to overlap. Although only one Pacific individual with a C. rastrinus-type Cytb gene was available for color evaluation, it was more similar to Pacific individuals than to Okhotsk Sea individuals. These results suggest inbreeding between C. pellucidus and C. rastrinus in the Pacific Ocean, off Miyagi Prefecture.

Contrasting population histories of the deep-sea demersal fish, Lycodes matsubarai, in the Sea of Japan and the Sea of Okhotsk.

Recent studies have revealed the impact of the drastic climate change during the last glacial period on coastal marine and anadromous species in the marginal seas of the northwestern Pacific Ocean; however, its influence on deep-sea species remains poorly understood. To compare the effects of the last glacial period on populations from the Sea of Japan and the Sea of Okhotsk, we examined the mitochondrial control region and cytochrome b gene sequences of Lycodes matsubarai, a deepsea demersal fish that inhabits these two seas. Our results showed clear genetic differentiation of populations between the two seas. The populations may have diverged during the last glacial period, probably as a result of vicariance due to the drastic sea level change. The population in the Sea of Okhotsk was larger than that in the Sea of Japan, but suddenly decreased after the last glacial period. However, the Sea of Japan population expanded after the last glacial period, coincident with high levels of oxygenation in deep-sea areas. These results elucidate regional-scale impacts of climate change on deep-sea organisms.