Koki Tsujii

Ogasawara Whale Watching Association

Sperm whales are known to prey on mesopelagic cephalopods such as giant squid. However, their predatory behavior has not yet been recorded as photographs or videos. If such images can be captured, it will be a valuable clue to clarify the predatory behavior. Therefore, we are developing the “whale rover” that is attached to the back of the whale an...

Humpback whales in the western North Pacific are considered endangered due to their small population size and lack of information. Although previous studies have reported interchanges between regions within a population, the relationship between the geographic regions of a population in Japan is poorly understood. Using 3,532 fluke photo IDs of uni...

Marine organisms inhabiting coastal waters are known to be driven by periodic cycles such as diel, tidal, and seasonal changes. Humpback whales (Megaptera novaeangliae) breed in shallow and warm coastal waters, with males singing complex songs during the breeding season. To investigate periodic variations in humpback whale singing activities, we co...

Sperm whales are known to have high diving ability and to prey on giant squid. Until now, several data (ex. diving depth, diving duration) have been obtained by bio-logging. However, it is difficult to photograph sperm whales preying on giant squid because loggers can adsorb only on their back. So far, we have developed a whale rover that can move...

The Chukchi Sea environment changes considerably in physical and biological conditions, driven by the expanding volume of warm Pacific summer water. These environmental changes can affect the migration timing of baleen whales in the southern Chukchi Sea. However, few studies have been conducted in this area to determine the migration timing of bowh...

The number of migrating fin whales (Balaenoptera physalus) appears to be increasing in the Pacific Arctic after changes in the marine ecosystem and recovering from depletion by commercial whaling. Fin whale songs are sequences of sounds produced repeatedly, and they may be used for population structure assessments. However, little is known about so...

Songs, which consist sequences of sounds produced repeatedly, have been produced by some baleen whales mainly for reproductive functions. Fin whale songs consist of regular sequences repeated 20 Hz pulses. Based on their Inter-pulse intervals (IPIs), their songs can be classified into some types. These types show geographic differences, therefore,...

The seasonal habitat use of bearded seals is important information in terms of conservation of this species. However, their distribution outside the breeding season has not been well documented. We investigated seasonal variations in the call occurrence of bearded seals by using passive acoustic monitoring in the southern Chukchi Sea, which has som...

Reactions of singing behavior of individual humpback whales (Megaptera novaeangliae) to a specific shipping noise were examined. Two autonomous recorders separated by 3.0 km were used for the acoustic monitoring of each individual song sequence. A passenger-cargo liner was operated once per day, and other large ship noise was excluded given the rem...

The variation between pre- and post-test periods in: (a) the mean of minimum frequency (Hz) with ship and (b) without ship; (c) the mean of maximum frequency (Hz) with ship and (d) without ship; (e) the mean of received sound level (dB rms re 1μPa) with ship and (f) without ship; (g) the mean of duration of units with ship and (h) without ship. The...

Mean (± SD) of minimum frequency (Hz) of received units during pre-test, test and post-test periods. (DOCX)

Mean (± SD) of sound pressure level (dB rms re 1μPa) of received units during pre-test, test and post-test periods. (DOCX)

Mean (± SD) of duration (sec) of received units during pre-test, test and post-test periods. (DOCX)

The consent form provided by Ogasawara Fisheries Cooperative Association (written in Japanese). (PDF)

The number of received units during pre-test, test and post-test periods. (DOCX)

A long baseline hydrophone array using two static recorders to monitor the singing behavior of humpback whales. (DOCX)

Mean (± SD) of maximum frequency (Hz) of received units during pre-test, test and post-test periods. (DOCX)

To assess how seasonal and ice-associated whales differently respond to the Arctic climate changes, understanding the relationships among their presence and environmental conditions is necessary. We examined the seasonal acoustic presence of fin Balaenoptera physalus and bowhead whales Balaena mysticetus in relation to prey abundance and oceanograp...

Ocean noise pollution is getting to be a major issue for the environmental assessment of maritime transportation and engineering. Evidences to estimate the effect of noise on marine creatures are urgently required. A Japanese team consist of government agency, universities, and research institutions launched a new project to observe possible effect...

Bearded seal Erignathus barbatus is one of ice-obligate species, which breeds on seasonal sea-ice in the Arctic and sub-Arctic during March-May. They are threatened by the rapid changes in the Arctic environment due to recent climate change, which causes sea-ice reduction or transition of their prey biomass. To understand the seasonal distribution...

Fin whales (Balaenoptera physalus) undergo seasonal migration in the Arctic Sea. Because their migration and distribution is likely affected by changes in global climate, we aimed to examine the migration timing of fin whales, and the relationship with prey availability within the oceanographic environment of the Arctic Sea, using passive and activ...

Environmental changes are considered to affect the migration and distribution of baleen whales in the Arctic region. We examined the seasonal acoustic presence of fin whales (Balaenoptera physalus) and the relationships between acoustics and oceanographic environments in the southern Chukchi Sea from July 2012 to October 2015. Fin whale calls were...