Papers by Sei-ichi Saitoh
Fisheries Science, 2002
In 1996, Japanese Fisheries Agency started management of fisheries resource by TAC (Total allowab... more In 1996, Japanese Fisheries Agency started management of fisheries resource by TAC (Total allowable catch). The management of the fisheries resource is an important issue. In this research, it was tried to elucidate the change of the fish resource by using the satellite data. The study fish is a sardine. Sardine resource around Japan repeats a big increasing and decreasing. Sardines catch volume increased rapidly in 80's, and decreased sharply in 90's. The change trend of an oceanic environment of the Touhoku sea area was presumed according to this multi satellite data at the period. The trend of the water temperature presumed from the satellite rose. On the other hand, the trend of Chlorophyll-a presumed from the satellite was descending. The data of the water temperature and Chlorophyll-a presumed the satellite was compared with the data of the sardine resource. As a result, a positive correlation was confirmed between Chlorophyll-a and the sardine resource of Oyashio water and perturbed water. On the other hand, a negative correlation was confirmed between the water temperature and the sardine resource.
Continental Shelf Research, Feb 1, 2012
ABSTRACT During the late summer of 1997, most of the continental shelf in the southeastern Bering... more ABSTRACT During the late summer of 1997, most of the continental shelf in the southeastern Bering Sea was covered by aquamarine-colored waters as a result of massive blooms of the coccolithophore, Emiliania huxleyi (E. huxleyi). Since then, E. huxleyi blooms in the eastern Bering Sea have become common. This study was conducted to examine spatio-temporal variability in E. huxleyi blooms in the eastern Bering Sea and to determine what factors are responsible for the blooms. In this study, we used datasets from the satellite ocean color sensor, SeaWiFS (Sea-viewing Wide Field-of-view Sensor) and MODIS (MODerate resolution Imaging Spectroradiometer) to detect the E. huxleyi blooms. The E. Huxley bloom was only found in the middle of the continental shelf domain (MSD), where the water depth is 20 to 100 m. We found large-scale interannual and seasonal variability in the area of the E. huxleyi blooms, with massive blooms observed in the spring of 1998 and 2000, and in the fall of 1997 and 2000. The blooms now typically peak in September, and only small bloom areas have also been observed since 2001.Here what we proposed is that the key parameter for the E. huxleyi blooms is the strength of the density stratification resulted from two water masses formed in different season, surface warm layer and cold bottom water (CBW). Warming of the CBW since 2001 in the middle shelf have induced weakening the aforementioned stratification during summer. With less stratification, the water column is much more easily mixed, resulting in an increased nutrient (nitrate and silicate) supply from subsurface layers by storms in the summer. This is likely to be responsible for the recent decrease in E. huxleyi blooms in the eastern Bering Sea shelf. Conversely, the strong stratification induced by an eruptive warming of surface layer and intensified cold bottom water may result in the development of the massive E. huxleyi blooms like in 1997.
Deep-sea Research Part Ii-topical Studies in Oceanography, 2002
ABSTRACT
Journal of Oceanography, Apr 27, 2010
Transaction of the Japan Society for Simulation Technology, 2012
International activities toward realizing smart fishing [1] are evolving to reduce their operatio... more International activities toward realizing smart fishing [1] are evolving to reduce their operational risks, greenhouse gas emissions and energy loss in response to recent hikes in the price of crude oil [2]. The state-of-the-art ocean simulation with spatiotemporally high resolutions can provide the detailed and accurate now/forecast of ocean currents, temperature and sealevel, and so on, which might help to improve the fishing efficiency [3]. The helpful information has to be correctly informed to the fishermen in order to achieve the smart fishing even if the now/forecasts of ocean states are perfectly accurate. However, the tremendous data of ocean states is daily produced by the operational forecast simulation aided by data assimilation system. Therefore, it is necessary that the beneficial information for good fishing operations is promptly extracted from deluged data sources of the ocean states and showed to the fishermen in time. In this study, we prove a comprehensive visual...
Pacific saury, Cololabis saira, a commercially important species for multi-national fishing fleet... more Pacific saury, Cololabis saira, a commercially important species for multi-national fishing fleets in northwestern Pacific is fished using bright lights to attract schools. The lights are easily monitored using night-time visible images from Defence Meteorological Satellite Program/Operational Linescan System (DMSP/OLS). Modeling the relationship between fishing light distribution and numbers of fishing vessels can facilitate near-real time prediction and management of saury fisheries. The objective of this study was to estimate the numbers of fishing vessels from night-time images and landing data in northwestern Pacific coast. Analysis was conducted in ArcGIS. Results show that spatial fishing light distribution is significantly related to numbers of fishing vessels. For instance, in September from 2003 to 2006, the number of emitted pixels was significantly correlated to number of fishing vessels. We suggest that it is possible to estimate fishing effort from remotely sensed nigh...
This paper presents an overview of a newly developed ubiquitous fi sheries information system usi... more This paper presents an overview of a newly developed ubiquitous fi sheries information system using satellite remote sensing and geographical information system (RS/GIS). The system was developed to aim for providing high value-added fi sheries oceanographic information in anytime and at anywhere. We also make this system to come into wide use for especially fi shermen and managers in fi sheries cooperation or fi sheries experimental stations. This system consists of four subsystems; MODIS (Moderate Resolution Imaging Spectroradiometer) receiving subsystem, database subsystem, analysis subsystem, and GIS subsystem (WebGIS and onboard-GIS). MODIS system provides sea surface temperature, chlorophyll-a concentration and sea ice distribution. Database manages the all products under Oracle software. Analysis subsystem produces level 1 to level 5 products, which include fi shing ground forecasting of Japanese common squid, Pacifi c saury, Skipjack tuna and Albacore tuna. These procedures run automatically, so that the fi shermen could receive information in near real time through communications satellites (maritime satellite internet services and digital packet communication services) and S-band Digital Multimedia Broadcasting (S-DMB) Service. Using satellite communication services, users can operate all products dynamically such as overlaying, measuring distance from nearest port or fi shing grounds on the onboard GIS. On the other hand, using S-DMB service, users can receive several marine information and weather information as broadcasting. Those systems can help to support effective fi shing activities such as economy with time for fi shing ground destination or nearest landing port. This ubiquitous information services promise to promote sustainable fi sheries operation and management in the offshore around Japan.
International Journal of Modeling, Simulation, and Scientific Computing, 2013
Recent studies are focusing on the distribution of water mass because the mixture region of water... more Recent studies are focusing on the distribution of water mass because the mixture region of water mass is highly related to the rich fishing grounds [Yasuda I., Watanabe Y., Fish. Oceanogr.3(3):172–181, 1994]. Due to the large data size and time-varying property, efficient exploration and visualization of the ocean data is always extremely challenging. To extract the dynamic behaviors of the water mass and its mixture from a large-scale simulated ocean dataset, we developed an efficient visualization system by applying our volume compression method and our volume rendering method. This system allows us to investigate the time-varying distributions of ocean physical properties, additionally from the user's perspective and requirements. In the experiments, we show the generality and expressiveness by applying our system for single- and multi-property visualizations to find some significant ocean water mass. Consequently, we could obtain a clear visualization result to show the dyn...
Progress in Oceanography, 2002
ICES Journal of Marine Science, 2012
Hirawake, T., Shinmyo, K., Fujiwara, A., and Saitoh, S. 2012. Satellite remote sensing of primary... more Hirawake, T., Shinmyo, K., Fujiwara, A., and Saitoh, S. 2012. Satellite remote sensing of primary productivity in the Bering and Chukchi Seas using an absorption-based approach. – ICES Journal of Marine Science, 69: . Ocean colour remote sensing has been utilized for studying primary productivity in the Arctic Ocean. However, phytoplankton chlorophyll a (Chl a) is not predicted accurately because of the interference of coloured dissolved organic matter (CDOM) and non-algal particles (NAP). To enhance the estimation accuracy, a phytoplankton absorption-based primary productivity model (ABPM) was applied to the Bering and Chukchi Seas. The phytoplankton absorption coefficient was determined correctly from sea surface remote sensing reflectance (Rrs) and reduced the effect of CDOM and NAP in primary productivity (PPeu) estimates. PPeu retrieved from in situ Rrs using the ABPM satisfied a factor of 2 of measured values. PPeu estimated from the Moderate Resolution Imaging Spectroradiomet...
Biogeosciences, 2011
Recent ocean warming and subsequent sea ice decline resulting from climate change could affect th... more Recent ocean warming and subsequent sea ice decline resulting from climate change could affect the northward shift of the ecosystem structure in the Chukchi Sea and Bering Sea shelf region (Grebmeier et al., 2006b). The size structure of phytoplankton communities provides an index of trophic levels that is crucial to understanding the mechanisms underlying such ecosystem changes and their implications for the future. This study proposes a new ocean color algorithm for deriving this characteristic by using the region's optical properties. The size derivation model (SDM) estimates the phytoplankton size index F L on the basis of sizefractionated chlorophyll-a (chl-a) using the light absorption coefficient of phytoplankton, a ph (λ), and the backscattering coefficient of suspended particles including algae, b bp (λ). F L was defined as the ratio of algal biomass attributed to cells larger than 5 µm to the total. It was expressed by a multiple regression model using the a ph (λ) ratio, a ph (488)/a ph (555), which varies with phytoplankton pigment composition, and the spectral slope of b bp (λ), γ , which is an index of the mean suspended particle size. A validation study demonstrated that 69 % of unknown data are correctly derived within F L range of ±20 %. The spatial distributions of F L for the cold August of 2006 and the warm August of 2007 were compared to examine application of the SDM to satellite remote sensing. The results suggested that phytoplankton size was responsive to changes in sea surface temperature. Further analysis of satellite-derived F L values and other environmental factors can advance our understanding of ecosystem structure changes in the shelf region of the Chukchi and Bering Seas.
Journal of Advanced Simulation in Science and Engineering, 2014
Frontiers in Marine Science
Japanese flying squid (Todarodes pacificus) is one of the most commercially important resources i... more Japanese flying squid (Todarodes pacificus) is one of the most commercially important resources in the Pacific Ocean and its abundance is largely affected by environmental conditions. We examined the influence of environmental factors in potential spawning grounds of the winter cohort, approximated from Japanese and South Korean catch and catch per unit effort (CPUE) data of Japanese flying squid. Annual spawning ground dynamics were constructed using sea surface temperature (SST), submarine elevation and mean Kuroshio axis data from 1979 to 2018. Based on these information, we generated a suite of spawning ground indices including suitability SST-weighted area of potential spawning ground (SSWA), mean values (January–April) of suitable SST (MVSS), and the meridional position (MP) of SST isolines (18–24°C). Comparable interannual-decadal variability patterns were detected between the squid abundance and spawning ground indices, with abrupt shifts around 1990/1991 and in recent decad...
IGARSS 2020 - 2020 IEEE International Geoscience and Remote Sensing Symposium, 2020
Radiometric calibration with the Moon (called the lunar calibration) is a promising method for ev... more Radiometric calibration with the Moon (called the lunar calibration) is a promising method for evaluating the performance of instruments onboard satellites orbiting around the Earth. In particular, the lunar calibration can provide inflight radiometric calibration opportunities for nano/microsatellites whose priorities are technical demonstrations and scientific observations during rather a short lifetime. In this study, we have applied the lunar calibration to a recently launched microsatellite named RISESAT. RISESAT had observed the Moon every month for a half year after the launch with an onboard instrument OOC. By simulating the Moon brightness for each observation based on the ROLO and SELENE/SP Moon models, we succeeded to measure < 2 % of a small degradation in four months. Further comparison of the observation and the simulation irradiance of the Moon revealed the bluing trend in the OOC's inter-band ratio.
Kasetsart University Fisheries Research Bulletin, 2010
Satellite-derived measurements were used to investigate the spatial and temporal variability of c... more Satellite-derived measurements were used to investigate the spatial and temporal variability of chlorophyll-a (Chl-a) and sea surface temperature (SST) at Regional Seas level in Thai waters. As case study, the Gulf of Thailand and Andaman Sea were selected as areas of interest (AOI). The monthly data with 4 km spatial resolution of Chl-a and SST ocean color images from January 2003 to December 2009 were collected from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Very High Resolution Radiometer (AVHRR), respectively. Chl-a concentration was relatively low during summer, while in winter Chl-a concentration increased and its relationship was inversely proportional with SST. The lowest Chl-a concentration was in August 2005 (0.33 mg m -3 ), while the highest was in December 2006 (0.96 mg m -3 ). The lowest SST was in January 2009 (27.12 °C) and the highest was in May 2005 (31.00 °C). Chl-a concentration has an important economic effect on coastal and marine en...
Deep Sea Research Part II: Topical Studies in Oceanography, 2018
Abstract The size structure of the phytoplankton community strongly affects energy flow through f... more Abstract The size structure of the phytoplankton community strongly affects energy flow through food webs; hence, monitoring the spatial and temporal dynamics of phytoplankton size structure is crucial to evaluate variability in marine ecosystems. In this study, the spatiotemporal changes in phytoplankton size structure and their impact on benthic macrofaunal distribution were examined in the Pacific Arctic as part of the international Distributed Biological Observatory effort. The exponent of the chlorophyll-a (Chla) size distribution (hereafter, CSD slope), which is an index of synoptic size structure of a phytoplankton community, was estimated based on spectral shape of the phytoplankton absorption coefficient using satellite ocean color data. The CSD slope during the post-bloom period was significantly correlated with sediment Chla concentration, suggesting that the amount of organic carbon input to the seafloor was strongly related to surface phytoplankton size structure after the spring bloom. Average macrofaunal biomass in the Pacific Arctic was persistently high (>20 g C m−2) throughout 2000–2013 in the regional hotspots, and the biomass-based latitudinal centroid of macrofaunal habitat in the region shifted significantly (p
International Journal of Remote Sensing, 2016
The present study used nighttime visible satellite images to identify the daily presence and abse... more The present study used nighttime visible satellite images to identify the daily presence and absence of the fishing vessel aggregations, targeting the Japanese common squid (Todarodes pacificus) in the coastal waters of southwestern Hokkaido, Japan. Here, statistical (generalized additive model (GAM) and generalized linear model (GLM)) and machine learning models (boosted regression tree (BRT)) were developed using a 3-year (2000-2002) presence/absence information from squid fishing aggregations and environmental variables (night-time sea surface temperature (SST), chlorophyll-a (Chl-a) concentration, K d (490) (diffuse attenuation coefficients of downwelling irradiance at 490 nm), and bathymetry). Our findings showed that BRT outperformed the regression-based models in predicting the potential squid fishing zones during the validation period (2003). Results from BRT indicated that potential fishing zones were closely associated with water depth. Both SST and Chl-a concentration were also found highly influential to squid occurrence, while K d (490), which is related to the water transparency, showed relatively less impact on the squid distribution. The spatial predictions using daily data from 2000 to 2003 revealed the gradual eastward movement of potential fishing zones between June and December, consistent with the pattern of squid fishing activities. Four experimental fishing surveys were further conducted to validate and improve our model predictions against experience-based fishing surveys. The results showed that the squid catches using our model predictions in 2012 substantially exceeded the average catches of experience-based fishing in 2011.
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Papers by Sei-ichi Saitoh