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Bower J.R.,Hokkaido University | Seki K.,Shiretoko Diving Kikaku | Kubodera T.,National Museum of Science and Nature | Yamamoto J.,Hokkaido University | Nobetsu T.,Shiretoko Nature Foundation
Biological Bulletin | Year: 2012

Brooding of egg masses by a squid in Japan is described. Brooding females were photographed in situ, and the females, their eggs, and their hatchlings were collected. The squid had all undergone gelatinous degeneration and swam slowly and continuously by undulating the fins and expelling water sporadically through the funnel. Eggs were held together by a dark, viscous material that formed a singlelayer, sheet-like mass, from which hatchlings were seen to emerge. The annual appearance of brooding females in surface waters during spring suggests that they transport their egg masses from deep water to the surface before the eggs hatch. Genetic analyses identified the squid as Gonatus madokai (family Gonatidae), now the second gonatid and third squid known to brood. © 2012 Marine Biological Laboratory.

Arima D.,Hokkaido University | Yamaguchi A.,Hokkaido University | Nobetsu T.,Shiretoko Nature Foundation | Imai I.,Hokkaido University
Crustaceana | Year: 2016

In the Okhotsk Sea, the calanoid copepod Metridia okhotensis Brodsky, 1950 is the dominant component of zooplankton, accounting for 61% of the annual mean total pelagic copepods. Although this organism is important, little ecological information is available for M. okhotensis in the Okhotsk Sea because of the ice cover during winter, which prevents the collection of seasonal samples in this region. Here, we report the seasonal changes in the population structure, sex ratio and female gonad maturation of M. okhotensis. The data are from samples collected using water pumped from a depth of 350 m off Rausu Harbour in the Okhotsk Sea at 2-week intervals over a 2.5-year period. Due to the mesh size of the strainer (420 μm), M. okhotensis was collected from C3 to adults. The sex ratio of C5 (female :male) was approximately 1 : 1 throughout the year. In contrast, the sex ratio of C6 (adult) showed a clear seasonality, with males (C6M) occurring only from December to May and females (C6F) dominating during the other seasons. The gonad maturation of C6F was scored using five categories, and their composition also showed clear seasonality. From January to April, gonads developed rapidly from stage I (immature) to V (spawning). During the other seasons, the majority of C6F had immature gonads. Based on these data, we conclude that this species likely has a diapause phase for C6F, with immature gonads, and C5M from June to November. Moulting from C5M to C6M began in December. Accompanying the occurrence of C6M, C6F were fertilized from December to January. C6F underwent gonad maturation from January to April and performed primary reproduction from April to May. Thereafter, M. okhotensis entered diapause from June to November. © Koninklijke Brill NV, Leiden, 2016.

Kohira M.,Shiretoko Nature Foundation | Mori S.-Y.,Shiretoko Raptor Society
Ursus | Year: 2010

We describe an incident we investigated in which a photographer on the Shiretoko Peninsula, Hokkaido, Japan observed a pair of adult brown bears (Ursus arctos yesoensis) mating on 11 October 2009. After an interview and examination of photographs, we conclude that the mating did occur on the reported date. Copulation evidently lasted about 30 minutes without overt struggle either before or after the event. Several days prior to the date, a female, which we presume to be the one involved, was seen with swollen and colored genitalia, suggesting she was in estrus. Only a single mating was witnessed and neither of the bears was observed after this date. Throughout its range, mating of brown bear is rarely observed in autumn, and this is probably the first record in Hokkaido. © 2010 International Association for Bear Research and Management.

Arima D.,Hokkaido University | Matsuno K.,Arctic Environmental Research Center | Yamaguchi A.,Hokkaido University | Nobetsu T.,Shiretoko Nature Foundation | Imai I.,Hokkaido University
Crustaceana | Year: 2015

The seasonal and inter-annual changes in the asymmetry of female insemination and the male leg 5 of the planktonic calanoid copepods Metridia okhotensis and M. pacifica were investigated in the Okhotsk Sea. An inter-species comparison of both parameters was also carried out on seven Metridia species collected from oceans throughout the world. For M. okhotensis from the Okhotsk Sea, most of the females showed left-side insemination (annual average: 95.7%) and most of the males showed left-side asymmetry (99.7%) of the long inner process of the second exopodal segment in the fifth leg throughout the year. However, sympatric M. pacifica showed different ratios of asymmetry for female insemination and male morphotypes with a left : right = 1 : 2 ratio throughout the year. For the seven Metridia species from the global oceans treated in this study, ratios of asymmetry for female insemination and male morphotypes were correlated with each other. One-sided insemination (i.e., only left or only right insemination) was a common pattern for various Metridia species from global oceans, but their ratios varied by species. Previously, low hatching rates (29-68%) of eggs were reported for various Metridia spp. in laboratory experiments, but the reasons for these low rates were unclear. Because each spermatheca of Metridia spp. is connected to the oviduct on the same side, either left or right, this suggests that half of the eggs produced by unilaterally inseminated females remain unfertilized. The morphology of the genital structures and literature data of the egg hatching rates of Metridia spp. indicate that almost half of the eggs produced by females are not viable and are, thus, wasted. © Koninklijke Brill NV, Leiden, 2015.

Yamamura O.,Hokkaido National Fisheries Research Institute | Nobetsu T.,Shiretoko Nature Foundation
Journal of the Marine Biological Association of the United Kingdom | Year: 2012

Food habits of threadfin hakeling Laemonema longipes, the dominant demersal fish in the upper continental slope of the western sub-Arctic North Pacific, were described based upon >1400 specimens collected off north-eastern Honshu Island and south-eastern Hokkaido Island, Japan. Threadfin hakeling depended exclusively on pelagic organisms including copepods Neocalanus cristatus, Euphausia pacifica, shrimps Sergestes similis, firefly squid Watasenia scintillans and myctophids Diaphus theta. Threadfin hakeling showed a clear size-dependent dietary variation, with mesozooplankton and shrimps being important for small-and medium-sized fish (≤400 mm standard length (SL)), and myctophids being important for large-sized fish (>400 mm SL). Since all of these prey undertake diurnal vertical migration, it was concluded that threadfin hakeling take an important role in capturing energy and materials transported from the epipelagic zone to the bathypelagic layer over the upper continental slope. Dietary variation among different areas, seasons and depths were also examined. Of these, areal difference was rather obscure reflecting common prey field in the Tohoku and Doto areas under the prevalence of the North Pacific Intermediate Water, whereas clear seasonal difference was found in the Doto area; the 0-group of walleye pollock Theragra chalcogramma was ingested only in the late summer and early autumn in this area. © 2011 Marine Biological Association of the United Kingdom.

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