The distributions and population dynamics of plant species are modified by environmental factors.... more The distributions and population dynamics of plant species are modified by environmental factors. The grazing intensity of herbivores may have major effects on aquatic plants. Lake Izunuma is located in the northeast of Japan and is one of the most famous wintering grounds for swans. The foraging activities of whooper swans (Cygnus cygnus) were observed frequently during the winter of 2011-2012. During the spring, the distribution of lotus (Nelumbo nucifera) differed in various locations and it seemed to be affected by the predation pressure of swans. Understanding the interactions between lotuses and whooper swans is essential for the appropriate control of lake ecosystems. Therefore, a more efficient monitoring system is needed to assess the status of the lake. In this study, we originally integrated a single-beam acoustic measurement system and conducted the in situ investigation of lotus root habitat under the lake bottom. The layer of maddy sand and lotus root were clearly detected by the measurement method. This novel survey method will contribute to sustainable management in the rapidly changing underwater environments found in lakes.
2013 IEEE International Underwater Technology Symposium (UT), 2013
Active acoustic monitoring system using a dual frequency identification sonar (DIDSON) is applied... more Active acoustic monitoring system using a dual frequency identification sonar (DIDSON) is applied for the follow-up observation of aquatic biota after Hydrilla verticillata planting. The field experiment was performed in a small pond adjacent to Lake Izunuma (northern latitude of 38.43 degrees and east longitude of 141.04 degrees; surface area, 1,584 m2), and 24 Hydrilla verticillata were prepared and planted at the pond bottom. The DIDSON unit was mounted on an original frame with a 3 degree concentrator lens. The data were collected at 1.8 MHz (high-frequency mode) and at a maximum range of 3.0 m from the imaging sonar. The frame rate was 2 fps and the recording time was about 20 hours. Successfully, we found out the cause of plants disappearance by the acoustic imaging data. All Hydrilla verticillata were disappeared in a day and strongly affected by the predation pressure of crayfish, and whole scene of feeding was recorded. Other aquatic creatures, such as snail, frog, and several species of fish, were also appeared in the acoustic images. Then, we have originally developed an image processing program and quantified the biological features of the aquatic creatures for the better understanding of aquatic biota in freshwater environment.
Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro w... more Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro were studied in barfin flounder Verasper moseri, masu salmon Oncorhynchus masou and goldfish Carassius auratus. Seabream GnRH (sbGnRH) at a dose of 200 ng/50 g body weight (BW) significantly increased plasma T4 levels 1 h after the in vivo injection in the barfin flounder, but thereafter the levels normalized.
The distributions and population dynamics of plant species are modified by environmental factors.... more The distributions and population dynamics of plant species are modified by environmental factors. The grazing intensity of herbivores may have major effects on aquatic plants. Lake Izunuma is located in the northeast of Japan and is one of the most famous wintering grounds for swans. The foraging activities of whooper swans (Cygnus cygnus) were observed frequently during the winter of 2011-2012. During the spring, the distribution of lotus (Nelumbo nucifera) differed in various locations and it seemed to be affected by the predation pressure of swans. Understanding the interactions between lotuses and whooper swans is essential for the appropriate control of lake ecosystems. Therefore, a more efficient monitoring system is needed to assess the status of the lake. In this study, we originally integrated a single-beam acoustic measurement system and conducted the in situ investigation of lotus root habitat under the lake bottom. The layer of maddy sand and lotus root were clearly detected by the measurement method. This novel survey method will contribute to sustainable management in the rapidly changing underwater environments found in lakes.
2013 IEEE International Underwater Technology Symposium (UT), 2013
Active acoustic monitoring system using a dual frequency identification sonar (DIDSON) is applied... more Active acoustic monitoring system using a dual frequency identification sonar (DIDSON) is applied for the follow-up observation of aquatic biota after Hydrilla verticillata planting. The field experiment was performed in a small pond adjacent to Lake Izunuma (northern latitude of 38.43 degrees and east longitude of 141.04 degrees; surface area, 1,584 m2), and 24 Hydrilla verticillata were prepared and planted at the pond bottom. The DIDSON unit was mounted on an original frame with a 3 degree concentrator lens. The data were collected at 1.8 MHz (high-frequency mode) and at a maximum range of 3.0 m from the imaging sonar. The frame rate was 2 fps and the recording time was about 20 hours. Successfully, we found out the cause of plants disappearance by the acoustic imaging data. All Hydrilla verticillata were disappeared in a day and strongly affected by the predation pressure of crayfish, and whole scene of feeding was recorded. Other aquatic creatures, such as snail, frog, and several species of fish, were also appeared in the acoustic images. Then, we have originally developed an image processing program and quantified the biological features of the aquatic creatures for the better understanding of aquatic biota in freshwater environment.
Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro w... more Effects of gonadotropin-releasing hormone (GnRH) on thyroxine (T4) release in vivo and in vitro were studied in barfin flounder Verasper moseri, masu salmon Oncorhynchus masou and goldfish Carassius auratus. Seabream GnRH (sbGnRH) at a dose of 200 ng/50 g body weight (BW) significantly increased plasma T4 levels 1 h after the in vivo injection in the barfin flounder, but thereafter the levels normalized.
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Papers by Yasufumi Fujimoto