No.77 (March,2010)
No.77 (March,2010)
A－446 Hiroki ASAMI, Hiroshi SHIMADA, Ryotaro ISHIDA and Shiro TAKAYANAGI
Interannual variabilities of a few dominant copepods abundances during spring in Ishikari Bay, western Hokkaido, Japan
Interannual variabilities of a few dominant copepods abundances through winter to spring were investigated from 2001 to 2004 at one station (J32) of central part of Ishikari Bay, western Hokkaido, established as one of the monitoring stations by Hokkaido Fisheries Experiment Station. Another station of near coastal area was added in only 2001. The maximum abundances of zooplankton were observed in May of all years, following by the spring phytoplankton blooms. Copepods were main components of total zooplankton abundances, and numerical compositions of copepods to total zooplankton abundances occupied more than 90% in their maximum level. Six copepod species such as Neocalanus spp., Mesocalanus tenuicornis, Pseudocalanus newmani, Clausocalanus pergens, Metridia pacifica, and Oithona spp. were determined as dominant species. Among them, three species of Neocalanus spp., P. newmani and M. pacifica were representative species in spring copepods community. As an another feature derived from the present study, Oithona spp. in April were the most numerous in 2001 of all four years. Ishikari herring of 2001 year class is known to be very strong. One of the possible factors of this strong year-class occurrence was discussed in relation to copepod variabilities.
Interannual variabilities of a few dominant copepods abundances through winter to spring were investigated from 2001 to 2004 at one station (J32) of central part of Ishikari Bay, western Hokkaido, established as one of the monitoring stations by Hokkaido Fisheries Experiment Station. Another station of near coastal area was added in only 2001. The maximum abundances of zooplankton were observed in May of all years, following by the spring phytoplankton blooms. Copepods were main components of total zooplankton abundances, and numerical compositions of copepods to total zooplankton abundances occupied more than 90% in their maximum level. Six copepod species such as Neocalanus spp., Mesocalanus tenuicornis, Pseudocalanus newmani, Clausocalanus pergens, Metridia pacifica, and Oithona spp. were determined as dominant species. Among them, three species of Neocalanus spp., P. newmani and M. pacifica were representative species in spring copepods community. As an another feature derived from the present study, Oithona spp. in April were the most numerous in 2001 of all four years. Ishikari herring of 2001 year class is known to be very strong. One of the possible factors of this strong year-class occurrence was discussed in relation to copepod variabilities.
A－447 Shiro TAKAYANAGI, Motohito YAMAGUCHI and Ryotaro ISHIDA
Changes in body length and proportion of mature fish at first spawning age in relation to strength of year class in the Ishikari Bay herring (Clupea pallasii Valenciennes)
Annual changes in body size and the proportion of mature fish at first spawning age (1 year old) were examined for the Ishikari Bay herring (Clupea pallasii) on the basis of samples collected during January and March from 1998 to 2007 in offshore waters, near the main spawning ground along the Sea of Japan coast in Hokkaido. The proportion of mature females varied from 27% (in the 2001 year class) to 100% (in the 1996, 1999 and 2002 year classes). Average fork length ranged from 217 mm (in the 2001 year class) to 245 mm (in the 2002 year class). On the other hand, the abundance of 1-year-old fish was extremely high in the 2001 year class and relatively low in the 1996-2000 and 2002-2003 year classes, and at a medium level in the 2004 and 2005 year classes. Spearman's rank correlation revealed significant correlations among the proportion of mature females, average fork length and stock number. These results suggest that body size and the proportion of mature fish are closely associated with strength of year class.
Annual changes in body size and the proportion of mature fish at first spawning age (1 year old) were examined for the Ishikari Bay herring (Clupea pallasii) on the basis of samples collected during January and March from 1998 to 2007 in offshore waters, near the main spawning ground along the Sea of Japan coast in Hokkaido. The proportion of mature females varied from 27% (in the 2001 year class) to 100% (in the 1996, 1999 and 2002 year classes). Average fork length ranged from 217 mm (in the 2001 year class) to 245 mm (in the 2002 year class). On the other hand, the abundance of 1-year-old fish was extremely high in the 2001 year class and relatively low in the 1996-2000 and 2002-2003 year classes, and at a medium level in the 2004 and 2005 year classes. Spearman's rank correlation revealed significant correlations among the proportion of mature females, average fork length and stock number. These results suggest that body size and the proportion of mature fish are closely associated with strength of year class.
A－448 Motohito YAMAGUCHI, Akio TAKIYA, Hiroshi YAMAGUCHI, Hiroya MIYAKE and Shiro TAKAYANAGI
The effects of stocking and fisheries management based on virtual population analysis of the Ishikari Bay herring Clupea pallasii
The catch of the Ishikari Bay herring (Clupea pallasii) has increased to about 200 tons since 1997. Virtual population analysis (VPA) has suggested that this increase was caused by greater recruitments of 1995 and 1996 year classes due to high recruitment per spawning biomass (RPS). The RPS rose again in 2001, and the 2001 year class increased the catch to more than 1,000 tons in 2004. Stocking and fisheries management have been conducted since 1996 and 2003, respectively. The effects of these measures were estimated to be 34 tons and 1,750 tons in fisheries year 2008 from calculation using VPA parameters. It is considered that the stocking and the fisheries management contributed synergistically to this increase in the catch.
The catch of the Ishikari Bay herring (Clupea pallasii) has increased to about 200 tons since 1997. Virtual population analysis (VPA) has suggested that this increase was caused by greater recruitments of 1995 and 1996 year classes due to high recruitment per spawning biomass (RPS). The RPS rose again in 2001, and the 2001 year class increased the catch to more than 1,000 tons in 2004. Stocking and fisheries management have been conducted since 1996 and 2003, respectively. The effects of these measures were estimated to be 34 tons and 1,750 tons in fisheries year 2008 from calculation using VPA parameters. It is considered that the stocking and the fisheries management contributed synergistically to this increase in the catch.
A－449 Shoichi AKAIKE, Kazuhiro TAKAHASHI, Hiroshi HOSHIKAWA, Akio TAKIYA, Fujinori TSUDA, Hiroo GODA, Kanji NAKAJIMA and Tadashi KAWAI
Distribution and abundance of the Ishikari Bay herring (Clupea pallasii) natural spawning beds and the seaweed beds on the northwestern coast of Hokkaido.
Distribution and abundance of natural spawning beds of Ishikari Bay herring (Clupea pallasii) were investigated along the northwestern coast of Hokkaido, Japan during 1996-2007. Geographic areas of seaweed beds were determined based on interpretation of aerial photographs using multispectoral images and color photographs taken during 1999-2004. Spawning beds were found at 1-7 sites per district after 1998. Their geographic distribution changed temporally from northern to southwestern districts and showed a wider range of depth shallower than 12m depth. The maximum number eggs was 381×108 at Atsuta district in 2004. This phenomenon was attributed to a large population of the 2001-year-class. The seaweed bed areas per district ranged 169×104-254×104㎡ except Wakkanai. More than 80 % seaweed beds were shallower than 5m depth. The percentage of seaweed bed area used as spawning beds were 4-9% at Rumoi district and<2% at other districts. The present seaweed beds areas are sufficient for herring spawning beds sustaining the present resource level. For enlarging the resource level, however, seaweed bed areas might be insufficient for spawning bed. Therefore, it will be necessary to preserve the present seaweed beds, restore degradated areas, and afforest a wider range of depth zones.
Distribution and abundance of natural spawning beds of Ishikari Bay herring (Clupea pallasii) were investigated along the northwestern coast of Hokkaido, Japan during 1996-2007. Geographic areas of seaweed beds were determined based on interpretation of aerial photographs using multispectoral images and color photographs taken during 1999-2004. Spawning beds were found at 1-7 sites per district after 1998. Their geographic distribution changed temporally from northern to southwestern districts and showed a wider range of depth shallower than 12m depth. The maximum number eggs was 381×108 at Atsuta district in 2004. This phenomenon was attributed to a large population of the 2001-year-class. The seaweed bed areas per district ranged 169×104-254×104㎡ except Wakkanai. More than 80 % seaweed beds were shallower than 5m depth. The percentage of seaweed bed area used as spawning beds were 4-9% at Rumoi district and<2% at other districts. The present seaweed beds areas are sufficient for herring spawning beds sustaining the present resource level. For enlarging the resource level, however, seaweed bed areas might be insufficient for spawning bed. Therefore, it will be necessary to preserve the present seaweed beds, restore degradated areas, and afforest a wider range of depth zones.
A－450 Noboru HOSHINO
Estimation method for age composition of Pacific cod (Gadus macrocephalus) in the Sea of Japan off the coast of Hokkaido.
Pacific cod (Gadus macrocephalus) is an important species caught by bottom trawling or gill net fisheries off the coast of Hokkaido, Japan. In Hokkaido, although fishing surveys at principal fishing ports have been conducted since the 1990s, the age compositions of cod caught by fisheries have not been estimated because of difficulties in obtaining an adequate number of fish samples. In this paper, I propose a mathematical method to estimate the age composition of fisheries products based on the Age Length Key (ALK) method using small numbers of samples and evaluate the accuracy of the estimates by computer simulations. This method showed a higher accuracy than the general purpose ALK method based on observed dates. Increasing the number of data sets ( i.e., number of samples ) used in estimating age compositions improved the accuracy of estimates, but showed little change in the simulation scenarios with more than 50 data sets. These results suggest that it may be possible to estimate the past age compositions based on the dates of previous fisheries surveys using this method. The age/length compositions of cod landed at the fishing ports of Yoichi and Otaru during the 2008 fishing season were estimated by this method in the applied case studies.
Pacific cod (Gadus macrocephalus) is an important species caught by bottom trawling or gill net fisheries off the coast of Hokkaido, Japan. In Hokkaido, although fishing surveys at principal fishing ports have been conducted since the 1990s, the age compositions of cod caught by fisheries have not been estimated because of difficulties in obtaining an adequate number of fish samples. In this paper, I propose a mathematical method to estimate the age composition of fisheries products based on the Age Length Key (ALK) method using small numbers of samples and evaluate the accuracy of the estimates by computer simulations. This method showed a higher accuracy than the general purpose ALK method based on observed dates. Increasing the number of data sets ( i.e., number of samples ) used in estimating age compositions improved the accuracy of estimates, but showed little change in the simulation scenarios with more than 50 data sets. These results suggest that it may be possible to estimate the past age compositions based on the dates of previous fisheries surveys using this method. The age/length compositions of cod landed at the fishing ports of Yoichi and Otaru during the 2008 fishing season were estimated by this method in the applied case studies.
A－451 Kenji SAKAGUCHI
Migration of tagged Japanese common squid, Todarodes pacificus, in waters around Hokkaido
Release and recapture records of tagged Japanese common squid, Todarodes pacificus, in the waters around Hokkaido are investigated. During 1927-2000, a total of 255,033 squid individuals were tagged and released, and 6,605 squids were recaptured. Migratory patterns of the squid were examined in the waters around Hokkaido, based on the results of the tagging experiments and the population structure. Todarodes pacificus migrate northeastward in the Sea of Japan and the Pacific Ocean with the warm Tsushima and Kuroshio currents, respectively. Then squid migrate southwestward utilizing the cold waters away from the warm current area at prior to spawning and dying of senescence in the warm currents.
Release and recapture records of tagged Japanese common squid, Todarodes pacificus, in the waters around Hokkaido are investigated. During 1927-2000, a total of 255,033 squid individuals were tagged and released, and 6,605 squids were recaptured. Migratory patterns of the squid were examined in the waters around Hokkaido, based on the results of the tagging experiments and the population structure. Todarodes pacificus migrate northeastward in the Sea of Japan and the Pacific Ocean with the warm Tsushima and Kuroshio currents, respectively. Then squid migrate southwestward utilizing the cold waters away from the warm current area at prior to spawning and dying of senescence in the warm currents.
A－452 Minoru SANO
Geographical distribution of Octopus dofleini fisheriesassessed for fisheries management using a geographic information system in the coastal areas around Hokkaido
Geographical distribution of the North Pacific giant octopus Octopus dofleini fishery in the coastal waters around Hokkaido was assessed for fisheries management purposes using a geographic information system. The assessment, based on the abundance of annual catch in licensed fishing grounds and annual changes in catch from 1985 to 2004, showed that the octopus fisheries could be classified into 11 areas around Hokkaido. These areas included the Soya Strait to the coastal area around Rishiri and Rebun Island, the Sea of Okhotsk, the Nemuro Strait, Pacific Ocean areas around eastern and southern Hokkaido, water area around Funka Bay mouth, the eastern and western Tsugaru Straits, coastal area around Okushiri Island, and the Japan Sea around western and northern Hokkaido. The geographical distribution of these local octopus fisheries in the coastal areas around Hokkaido are well suited to fisheries management.
Geographical distribution of the North Pacific giant octopus Octopus dofleini fishery in the coastal waters around Hokkaido was assessed for fisheries management purposes using a geographic information system. The assessment, based on the abundance of annual catch in licensed fishing grounds and annual changes in catch from 1985 to 2004, showed that the octopus fisheries could be classified into 11 areas around Hokkaido. These areas included the Soya Strait to the coastal area around Rishiri and Rebun Island, the Sea of Okhotsk, the Nemuro Strait, Pacific Ocean areas around eastern and southern Hokkaido, water area around Funka Bay mouth, the eastern and western Tsugaru Straits, coastal area around Okushiri Island, and the Japan Sea around western and northern Hokkaido. The geographical distribution of these local octopus fisheries in the coastal areas around Hokkaido are well suited to fisheries management.
A－453 Yutaka NISHIHARA
Infection of protozoan Perkinsus in the short-necked clam (Ruditapes philippinarum) on the Hokkaido coastal region and the infection examination.
The Ray’s fluid thioglycollate medium (RFTM) assay technique was used to study Perkinsus infection in the short-necked clam (Ruditapes philippinarum) in the Hokkaido coastal region between 1999 and 2001. Formation conditions for the Perkinsus zoospore were observed, with particular attention to favorable temperature and salinity ranges. The zoospore was then cultured with short-necked clam tissues and experimentally infected into short-necked clam, Japanese scallop (Patinopecten yessoensis), Japanese oyster (Crassostrea gigas), and Ezo abalone (Haliotis discus hannai) at various temperatures. The protozoan was not detected in the Pacific Ocean or the Okhotsk Sea, but it was detected at all tested locations in the Sea of Japan. No effect on zoospore formation was observed to result from variation in salinity (0-3‰). In the laboratory, zoospore formation was observed at 20°C and 25°C, but not at 15°C. In the lab portion of the study, however, when Perkinsus infection was attempted at 20°C infection was not confirmed in any of the four tested species. At 25°C, however, infection was confirmed in the short-necked clam.
The Ray’s fluid thioglycollate medium (RFTM) assay technique was used to study Perkinsus infection in the short-necked clam (Ruditapes philippinarum) in the Hokkaido coastal region between 1999 and 2001. Formation conditions for the Perkinsus zoospore were observed, with particular attention to favorable temperature and salinity ranges. The zoospore was then cultured with short-necked clam tissues and experimentally infected into short-necked clam, Japanese scallop (Patinopecten yessoensis), Japanese oyster (Crassostrea gigas), and Ezo abalone (Haliotis discus hannai) at various temperatures. The protozoan was not detected in the Pacific Ocean or the Okhotsk Sea, but it was detected at all tested locations in the Sea of Japan. No effect on zoospore formation was observed to result from variation in salinity (0-3‰). In the laboratory, zoospore formation was observed at 20°C and 25°C, but not at 15°C. In the lab portion of the study, however, when Perkinsus infection was attempted at 20°C infection was not confirmed in any of the four tested species. At 25°C, however, infection was confirmed in the short-necked clam.
A－454 Hidetsugu YOSHIDA, Yoshiyuki TAKAYA and Taihei MATSUDA
Recapture age and total length of tagged barfin flounder Verasper moseri in Funka Bay and the coastal waters of Hidaka area, southwestern Hokkaido (Short Paper）