This study analysed post-1900 published and unpublished records of gray whales in the western Nor... more This study analysed post-1900 published and unpublished records of gray whales in the western North Pacific. Modern whaling recorded a peak annual catch of 100-200 whales in the 1910s, followed by a rapid decline in the 1920s and 1930s and a continued low level (perhaps 10-20 whales/year) for over 40 years to the l960s. Catches made during the last phase could have been the major factor suppressing recovery until recently. There are reasons to believe that this gray whale stock breeds in Hainan waters.
Ocean ambient noises against seismic signals are well studied using archived waveforms recorded o... more Ocean ambient noises against seismic signals are well studied using archived waveforms recorded on three-component seismometers and hydrophones connected to a seafloor cabled seismic network off Kushiro, Hokkaido, Japan basically facing the Pacific Ocean. The system was deployed to install in late July 1999 by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Outstanding “noises” at frequency bands of 15-30 Hz are recorded on all components of both seismometers and hydrophones, which are directly recognized as fin whale calls in comparison with in-situ visual surveys carried in September to October 2009. It is extremely conspicuous that a seasonal variation of the fin whale calls has been revealed in ambient noise spectrograms of continuous longterm waveform records from 2009 to 2013. High-intensity signals associated with the fin whale calls appear commonly in the periods from September to February over cold winter at high latitudes. The remarkable seasonal pattern should be corresponded to their annual living behavior and might be related to climate changes in the Pacific Ocean.
origin, objectives and research progress made in the period 2002-2007, including scientific consi... more origin, objectives and research progress made in the period 2002-2007, including scientific considerations for the next research period
TransNav: International Journal on Marine Navigation and Safety of Sea Transportation, 2012
In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (U... more In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (UWS) has been installed on the HF. Because of its potential in utility, the authors tried to improve the UWS to minimize the risk of the collisions. Under the project, they examined three subprojects; 1) Analyzing the characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise with approximately 150dB re 1μPa-m. That noise level was lower than those of larger boats suggesting difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and anatomical observation indicated that dominant frequency of their audible range was lower than signals produced by the existing UWS.
We analyzed the seismic data from 2009 to 2013 obtained from seafloor cable seismic network off K... more We analyzed the seismic data from 2009 to 2013 obtained from seafloor cable seismic network off Kushiro, Hokkaido, Japan, which was deployed by Japan Agency for Marine Earth Science and Technology in 1999. Two kinds of calls were recorded, one is “Single” which is not related to the preceding and following intervals, and the other is “Doublet” which alternates short intervals and long intervals. Especially the interval of “Doublet” shows a seasonal change, it is characterized as a long interval in January and February, while becomes shorter interval in October and November. It is quite unlikely that the same group of fin whales are calling while the call is appearing off Kushiro. The seasonal change of “Doublet” might be a change of the group appearing off Kushiro.
This study analysed post-1900 published and unpublished records of gray whales in the western Nor... more This study analysed post-1900 published and unpublished records of gray whales in the western North Pacific. Modern whaling recorded a peak annual catch of 100-200 whales in the 1910s, followed by a rapid decline in the 1920s and 1930s and a continued low level (perhaps 10-20 whales/year) for over 40 years to the l960s. Catches made during the last phase could have been the major factor suppressing recovery until recently. There are reasons to believe that this gray whale stock breeds in Hainan waters.
Ocean ambient noises against seismic signals are well studied using archived waveforms recorded o... more Ocean ambient noises against seismic signals are well studied using archived waveforms recorded on three-component seismometers and hydrophones connected to a seafloor cabled seismic network off Kushiro, Hokkaido, Japan basically facing the Pacific Ocean. The system was deployed to install in late July 1999 by Japan Agency for Marine-Earth Science and Technology (JAMSTEC). Outstanding “noises” at frequency bands of 15-30 Hz are recorded on all components of both seismometers and hydrophones, which are directly recognized as fin whale calls in comparison with in-situ visual surveys carried in September to October 2009. It is extremely conspicuous that a seasonal variation of the fin whale calls has been revealed in ambient noise spectrograms of continuous longterm waveform records from 2009 to 2013. High-intensity signals associated with the fin whale calls appear commonly in the periods from September to February over cold winter at high latitudes. The remarkable seasonal pattern should be corresponded to their annual living behavior and might be related to climate changes in the Pacific Ocean.
origin, objectives and research progress made in the period 2002-2007, including scientific consi... more origin, objectives and research progress made in the period 2002-2007, including scientific considerations for the next research period
TransNav: International Journal on Marine Navigation and Safety of Sea Transportation, 2012
In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (U... more In order to avoid collisions between the hydrofoil (HF) and cetaceans, the Under Water Speaker (UWS) has been installed on the HF. Because of its potential in utility, the authors tried to improve the UWS to minimize the risk of the collisions. Under the project, they examined three subprojects; 1) Analyzing the characteristics of the HF underwater noise; 2) Assessing audibility of major large cetaceans by measuring their vocalizations and 3) An anatomical prediction of the audible range by examining the cochlear basal membrane. Through the analyses, it was identified that the noise produced by the HF was a broad-band noise with approximately 150dB re 1μPa-m. That noise level was lower than those of larger boats suggesting difficulties for cetaceans in sensing approach of the vessels. In addition, analysis of their vocalizations and anatomical observation indicated that dominant frequency of their audible range was lower than signals produced by the existing UWS.
We analyzed the seismic data from 2009 to 2013 obtained from seafloor cable seismic network off K... more We analyzed the seismic data from 2009 to 2013 obtained from seafloor cable seismic network off Kushiro, Hokkaido, Japan, which was deployed by Japan Agency for Marine Earth Science and Technology in 1999. Two kinds of calls were recorded, one is “Single” which is not related to the preceding and following intervals, and the other is “Doublet” which alternates short intervals and long intervals. Especially the interval of “Doublet” shows a seasonal change, it is characterized as a long interval in January and February, while becomes shorter interval in October and November. It is quite unlikely that the same group of fin whales are calling while the call is appearing off Kushiro. The seasonal change of “Doublet” might be a change of the group appearing off Kushiro.
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