No.78 (October,2010)
No.78 (October,2010)
A－455 Hiroshi YAMAGUCHI
Development of stock management evaluation procedure incorporating uncertainty from sampling error
Uncertainty is a central assignment of fish stock management. This study developed the stock management evaluation procedure incorporating uncertainty to provide the useful information for the members participating stock management. To evaluate stock management candidates, 30-year population dynamics, including uncertainties, were simulated. Errors in current stock size estimation by bootstrap methods, variability in future recruitment, and changes in future fishing mortalities were incorporated. The evaluation of stock management candidates were conducted through four axes performance indexes. The efficiency of the simulation model was examined through its application to real stock. The walleye pollock Theragra chalcogramma stock and the pointhead flounder Cleisthenes pinetorum stock were selected for simulation model. The ratios of measurement errors in abundance estimates were relatively small in both stock and the ratios were 1% to 59 %. The evaluation of stock management candidates were shown the similar tendency in both stock application. The severe regulation candidates were more effective than loose regulation candidates in the conservation performance. The utilization performance obtained in both stock showed their evaluation were different with differing period length. A quantitative evaluation procedure including the uncertainties from sampling error was developed in this study. This procedure could enrich discussions of the effects of a variety of management actions when stakeholders are considering various requirements of the stock.
Uncertainty is a central assignment of fish stock management. This study developed the stock management evaluation procedure incorporating uncertainty to provide the useful information for the members participating stock management. To evaluate stock management candidates, 30-year population dynamics, including uncertainties, were simulated. Errors in current stock size estimation by bootstrap methods, variability in future recruitment, and changes in future fishing mortalities were incorporated. The evaluation of stock management candidates were conducted through four axes performance indexes. The efficiency of the simulation model was examined through its application to real stock. The walleye pollock Theragra chalcogramma stock and the pointhead flounder Cleisthenes pinetorum stock were selected for simulation model. The ratios of measurement errors in abundance estimates were relatively small in both stock and the ratios were 1% to 59 %. The evaluation of stock management candidates were shown the similar tendency in both stock application. The severe regulation candidates were more effective than loose regulation candidates in the conservation performance. The utilization performance obtained in both stock showed their evaluation were different with differing period length. A quantitative evaluation procedure including the uncertainties from sampling error was developed in this study. This procedure could enrich discussions of the effects of a variety of management actions when stakeholders are considering various requirements of the stock.
A－456 Noboru HOSHINO
Evaluation of Pacific cod (Gadus macrocephalus) stocks in the Sea of Japan off Hokkaido.
The catch of Pacific cod (Gadus macrocephalus), one of the most important species in the coastal waters off Hokkaido in the Sea of Japan, has been decreasing in recent years. In this study, Pacific cod stocks were evaluated based on verification of catch fluctuation, estimation of catch-at-age in each fishery, and stock size by VPA. The catch trend in each fishery, except that in the coastal sea area off Souya, has been decreasing since 2000, especially for the offshore trawl fishery. The fishing season has changed to spring (February to April), resulting in a decrease in the ratio of the catch from December to January, which was the major fishing season previously. Stock size estimated using VPA fluctuated between 25,000 and 30,000 tons in the first half of the 1990s; however, it has been reduced to less than 10,000 tons in recent years. One reason for the decline in stock is that the stock-recruitment relationships (RPSs) for the 1994, 1995, and 1996 year classes showed a continuous change to a lower level. Although RPSs for the 1997, 2000, and 2005 year classes were at a higher level, their recruitment sizes did not have sufficient capability for enhancing the stock size because of the lower maternal stock size. These results suggest a necessity for the fisheries management plan to increase the spawning stock biomass.
The catch of Pacific cod (Gadus macrocephalus), one of the most important species in the coastal waters off Hokkaido in the Sea of Japan, has been decreasing in recent years. In this study, Pacific cod stocks were evaluated based on verification of catch fluctuation, estimation of catch-at-age in each fishery, and stock size by VPA. The catch trend in each fishery, except that in the coastal sea area off Souya, has been decreasing since 2000, especially for the offshore trawl fishery. The fishing season has changed to spring (February to April), resulting in a decrease in the ratio of the catch from December to January, which was the major fishing season previously. Stock size estimated using VPA fluctuated between 25,000 and 30,000 tons in the first half of the 1990s; however, it has been reduced to less than 10,000 tons in recent years. One reason for the decline in stock is that the stock-recruitment relationships (RPSs) for the 1994, 1995, and 1996 year classes showed a continuous change to a lower level. Although RPSs for the 1997, 2000, and 2005 year classes were at a higher level, their recruitment sizes did not have sufficient capability for enhancing the stock size because of the lower maternal stock size. These results suggest a necessity for the fisheries management plan to increase the spawning stock biomass.
A－457 Noboru HOSHINO
Characteristics of juvenile sand eel (Ammodytes personatus) fishing in the north coastal waters off Shiribeshi, Hokkaido.
The catch of juvenile sand eel (Ammodytes personatus), one of the most important species in Shiribeshi, Hokkaido, has been decreasing in recent years, especially in northern Shiribeshi. The characteristics of the fishery products and catch fluctuations were investigated in order to understand the recruitment mechanism of sand eel stock in northern Shiribeshi. Using otolith (lapillus) increment analysis, the frequency distributions of hatch dates sampled in northern Shiribeshi were shown to be polymodal as is the case in southern Shiribeshi, suggesting that spawning intense on several occations during each fishing season. For each year, the mean individual growth rate in northern Shiribeshi was greater than that in southern Shiribeshi. Factor analysis for catch fluctuations at each fishing site in Shiribeshi indicated that the spawning site of northern Shiribeshi stock was in the coastal sea around Cape Syakotan. The decrease in the sand eel catch in northern Shiribeshi may be attributed to a decline of spawning sites around Cape Syakotan.
The catch of juvenile sand eel (Ammodytes personatus), one of the most important species in Shiribeshi, Hokkaido, has been decreasing in recent years, especially in northern Shiribeshi. The characteristics of the fishery products and catch fluctuations were investigated in order to understand the recruitment mechanism of sand eel stock in northern Shiribeshi. Using otolith (lapillus) increment analysis, the frequency distributions of hatch dates sampled in northern Shiribeshi were shown to be polymodal as is the case in southern Shiribeshi, suggesting that spawning intense on several occations during each fishing season. For each year, the mean individual growth rate in northern Shiribeshi was greater than that in southern Shiribeshi. Factor analysis for catch fluctuations at each fishing site in Shiribeshi indicated that the spawning site of northern Shiribeshi stock was in the coastal sea around Cape Syakotan. The decrease in the sand eel catch in northern Shiribeshi may be attributed to a decline of spawning sites around Cape Syakotan.
A－458 Izumi SAKURAI, Isao ONO, and Hideo ISHIDA
Construction of Cystoseira hakodatensis seaweed beds: study of optimal placement conditions for epiphytic substrata
A study was conducted to examine the optimal placement conditions of epiphytic substrata for thalli of Cystoseira hakodatensis in the construction of seaweed beds off the coast of Noboribetsu, Hokkaido, Japan. The substrata were placed at various water depths in May 2009 by adjusting the height of plinth blocks. The density and growth of thalli on the substrata were measured, in addition to counting the individual numbers of herbivorous animals, in October and December. Observations of wave, littoral drift and light intensity were conducted in parallel. The density and growth of thalli tended to decrease with water depth, in association with increased littoral drift and a decline of light intensity. Temporal changes in light intensity seemed to be synchronized with those of wave action. Although two herbivorous limpets, Omphaliusrusticus and Acmaea pallida, were found, their distribution was limited to certain substrata. It is suggested that a major factor limiting the density and growth of thalli is a decline of light intensity and an increase of littoral drift due to wave action. Accordingly, the substrata need to be placed at a depth where cumulative photon flux density remains at more than 0.7 mol/m2/day when constructing seaweed beds of C. hakodatensis.
A study was conducted to examine the optimal placement conditions of epiphytic substrata for thalli of Cystoseira hakodatensis in the construction of seaweed beds off the coast of Noboribetsu, Hokkaido, Japan. The substrata were placed at various water depths in May 2009 by adjusting the height of plinth blocks. The density and growth of thalli on the substrata were measured, in addition to counting the individual numbers of herbivorous animals, in October and December. Observations of wave, littoral drift and light intensity were conducted in parallel. The density and growth of thalli tended to decrease with water depth, in association with increased littoral drift and a decline of light intensity. Temporal changes in light intensity seemed to be synchronized with those of wave action. Although two herbivorous limpets, Omphaliusrusticus and Acmaea pallida, were found, their distribution was limited to certain substrata. It is suggested that a major factor limiting the density and growth of thalli is a decline of light intensity and an increase of littoral drift due to wave action. Accordingly, the substrata need to be placed at a depth where cumulative photon flux density remains at more than 0.7 mol/m2/day when constructing seaweed beds of C. hakodatensis.
A－459 Akiyoshi SHINADA, Masahide TADA, Yasuto NISHINO and Toshifumi KAWAJIRI
Spatial distribution of hypoxic water in Lake Notoro (Short paper)
A－460 Toru SATO, Masayuki SAWAMURA and Masaki MITSUHASHI
Hatching dates of the Japanese common squid,Todarodes pacificus, in the coastal waters of southern Hokkaido and Tohoku in summer 2005 and 2006（Short Paper)