Seasonal variations of shelf circulation in Hidaka Bay,Hokkaido, Japan,with an interpretation of the migration route of juvenile walleye pollock |
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| Authors: | Ana Luisa Rosa Yutaka Isoda Naoto Kobayashi |
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| Institution: | (1) Seward Marine Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, P.O. Box 730, Seward, Alaska, 99664-0730, USA;(2) Alaska SeaLife Center, P.O. Box 1329, Seward, Alaska, 99664-1329, USA;(3) Fishery Industrial Technology Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, 118 Trident Way, Kodiak, Alaska, 99615-7401, USA;(4) Institute of Marine Science, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, P.O. Box 757220, Fairbanks, Alaska, 99775-7220, USA;(5) Present address: School for Marine Science and Technology, University of Massachusetts Dartmouth, 706 South Rodney French Boulevard, New Bedford, MA 02744-1221, USA;(6) Present address: Kodiak Laboratory, Alaska Fisheries Science Center, National Oceanic and Atmospheric Administration, Kodiak Fisheries Research Center, 301 Research Court, Kodiak, Alaska, 99615-7400, USA |
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| Abstract: | The outer shelf of Funka Bay, located at the bay head of Hidaka Bay, is a recognised main winter spawning ground for walleye
pollock (Theragra chalcogramma), whose newly hatched juveniles migrate eastward along the Hidaka shelf to the nursery ground located in the Doto area. To
examine the seasonal change of the coastal current along this migration route, four current moorings were deployed along the
shelf in Hidaka Bay from April, 2004 to June, 2006. Since these mooring sites were close to the coast, the circulation was
estimated after removal of the wind-driven component. It was found that the winter coastal flow, forced by a north-westerly
monsoon wind, is clockwise along the Hidaka shelf. However, this flow is weak due to the superimposition of the opposite Coastal
Oyashio flow trapped on the shelf. In summer, a bifurcation of the coastal current occurs along the north-eastern Hidaka shelf
with a south-eastward flow, associated with the Tsugaru Gyre, and a north-westward flow, consisting of a branch from this
gyre. Our results provide a new understanding of the migration of juvenile walleye pollock: (1) very slow transport of juveniles
along the Hidaka shelf from winter to spring, and (2) selection of earlier spawning survivors due to the bifurcated flow in
early summer. |
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