No.75 (March,2009)
No.75 (March,2009)
A－429 Akiyoshi SHINADA , Hajime OMORI, Masahide TADA, Yasuhito NISHINO and Tomoki SATO
Effect of wind on behavior of hypoxic water in Lake Notoro
Effect of wind on behavior of hypoxic water was examined to prevent fishery damages in Lake Notoro from 18 to 27 September 2007. Vertical and horizontal distributions of water temperature, salinity and dissolved oxygen were investigated. Wind data was obtained from the web site of the Meteorological Agency. Although average wind velocities were less than ca. 4 m s-1 until 24 September, it became more than 6 m s-1 from 25 to 26 September. The hypoxic water was observed at bottom of shallow station on 18 and 20 September, and then it disappeared at all stations after 25 September. These results coincide with information reported by numerical simulation, which indicated deep water lifted due to less than 4 m s-1 of average wind velocity and the stratification was destroyed when wind velocity was more than 6 m s-1. Therefore, wind might have strong effect on behavior of hypoxic water in Lake Notoro. We analyzed year-to-year variation of average wind velocity in summer from 1998 to 2007. This analysis indicates that the probability, which is days under 4 m s-1 of average wind velocity continues for more than 50 days, is very low. The monitoring of average wind velocity could be one of the useful index to precaution against behavior of hypoxic water.
Effect of wind on behavior of hypoxic water was examined to prevent fishery damages in Lake Notoro from 18 to 27 September 2007. Vertical and horizontal distributions of water temperature, salinity and dissolved oxygen were investigated. Wind data was obtained from the web site of the Meteorological Agency. Although average wind velocities were less than ca. 4 m s-1 until 24 September, it became more than 6 m s-1 from 25 to 26 September. The hypoxic water was observed at bottom of shallow station on 18 and 20 September, and then it disappeared at all stations after 25 September. These results coincide with information reported by numerical simulation, which indicated deep water lifted due to less than 4 m s-1 of average wind velocity and the stratification was destroyed when wind velocity was more than 6 m s-1. Therefore, wind might have strong effect on behavior of hypoxic water in Lake Notoro. We analyzed year-to-year variation of average wind velocity in summer from 1998 to 2007. This analysis indicates that the probability, which is days under 4 m s-1 of average wind velocity continues for more than 50 days, is very low. The monitoring of average wind velocity could be one of the useful index to precaution against behavior of hypoxic water.
A－430 Nozomi OKADA, Hiroki ASAMI and Motohito YAMAGUCHI
Distribution and feeding habits of shirauo, Salangichthys microdon, in the Ishikari River system and adjacent nearshore areas, western Hokkaido
Larvae and early juveniles of shirauo, Salangichthys microdon, inhabiting the Ishikari River system and its adjacent nearshore areas exhibit two migration patterns: some of them reside in the estuary-sea area while others migrate upstream toward the oxbow lake. To evaluate the importance of the oxbow lake as a feeding ground after the upstream migration, the feeding habits of shirauo were examined in August 2001. Shirauo preyed selectively on a type of cladoceran (Diaphanosoma brachyurum) in the oxbow lake and on some copepods (Paracalauns parvus, Pseudodiaptomus marinus, etc.) in the estuary and nearshore waters. Surveys on the distribution of zooplankton have revealed that cladocerans are much more abundant in oxbow lakes, while the densities of cladocerans and prey copepods are low in the sea area. We concluded that the oxbow lake of the Ishikari River was a better feeding ground for shirauo larvae and early juveniles migrating in the summer.
Larvae and early juveniles of shirauo, Salangichthys microdon, inhabiting the Ishikari River system and its adjacent nearshore areas exhibit two migration patterns: some of them reside in the estuary-sea area while others migrate upstream toward the oxbow lake. To evaluate the importance of the oxbow lake as a feeding ground after the upstream migration, the feeding habits of shirauo were examined in August 2001. Shirauo preyed selectively on a type of cladoceran (Diaphanosoma brachyurum) in the oxbow lake and on some copepods (Paracalauns parvus, Pseudodiaptomus marinus, etc.) in the estuary and nearshore waters. Surveys on the distribution of zooplankton have revealed that cladocerans are much more abundant in oxbow lakes, while the densities of cladocerans and prey copepods are low in the sea area. We concluded that the oxbow lake of the Ishikari River was a better feeding ground for shirauo larvae and early juveniles migrating in the summer.
A－431 Akiyoshi SHINADA
Effects of summer water temperature and food concentration on the growth of bottom cultured Japanese scallop Mizuhopecten yessoensis and the outbreak of paralytic shellfish poisoning (PSP), in the coastal area of northeastern part of Hokkaido, Japan. (Short Paper)
A－432 Yoshiyuki TAKAYA, Hidetsugu YOSHIDA, Taihei MATSUDA and Osamu MURAKAMI
Migration of hatchery-reared barfin flounder Veraspar moseri with their age in the Pacific coastal waters off southwestern Hokkaido, Japan (Short paper)
A－433 Yoshiyuki TAKAYA, Osamu MURAKAMI，Hidetsugu YOSHIDA, Takaaki KAYABA and Taihei MATSUDA
Sex ratio of released and recaptured barfin flounder Verasper moseri in the Pacific coastal waters off southwestern Hokkaido, Japan (Short paper)
A－434 Koji TSUJI，Akiyuki SATO，Hiromi KANEKO and Hiroshi NOMATA
Changes in the quality of the dark and white muscle of Pacific saury,Cololabis saira, during storage in ice (Short Paper)