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Linnenschmidt M.,University of Southern Denmark | Teilmann J.,University of Aarhus | Akamatsu T.,Japan National Research Institute of Fisheries Engineering | Akamatsu T.,Japan Science and Technology Agency | And 2 more authors.
Marine Mammal Science | Year: 2013

This study presents bioacoustic recordings in combination with movements and diving behavior of three free-ranging harbor porpoises (a female and two males) in Danish waters. Each porpoise was equipped with an acoustic data logger (A-tag), a time-depth-recorder, a VHF radio transmitter, and a satellite transmitter. The units were programmed to release after 24 or 72 h. Possible foraging occurred mostly near the surface or at the bottom of a dive. The porpoises showed individual diversity in biosonar activity (<100 to >50,000 clicks per hour) and in dive frequency (6-179 dives per hour). We confirm that wild harbor porpoises use more intense clicks than captive animals. A positive tendency between number of dives and clicks per hour was found for a subadult male, which stayed near shore. It showed a distinct day-night cycle with low echolocation rates during the day, but five times higher rates and higher dive activity at night. A female traveling in open waters showed no diel rhythm, but its sonar activity was three times higher compared to the males'. Considerable individual differences in dive and echolocation activity could have been influenced by biological and physical factors, but also show behavioral adaptability necessary for survival in a complex coastal environment. © 2012 by the Society for Marine Mammalogy.


Rasmussen M.H.,University of Iceland | Akamatsu T.,Japan National Research Institute of Fisheries Engineering | Teilmann J.,University of Aarhus | Vikingsson G.,Iceland Marine Research Institute | Miller L.A.,University of Southern Denmark
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

For the first time bio-logging tags were attached to free-ranging white-beaked dolphins, Lagenorhynchus albirostris. A satellite tag was attached to one animal while an acoustic A-tag, a time-depth recorder and a VHF transmitter complex was attached to a second dolphin with a suction cup. The satellite tag transmitted for 201 day, during which time the dolphin stayed in the coastal waters of western Iceland. The acoustic tag complex was on the second animal for 13. h and 40. min and provided the first insight into the echolocation behaviour of a free-ranging white-beaked dolphin. The tag registered 162 dives. The dolphin dove to a maximum depth of 45. m, which is about the depth of the bay in which the dolphin was swimming. Two basic types of dives were identified; U-shaped and V-shaped dives. The dolphin used more time in U-shaped dives, more clicks and sonar signals with shorter click intervals compared to those it used in V-shaped dives. The dolphin was in acoustic contact with other dolphins about five hours after it was released and stayed with these for the rest of the tagging time. Possible foraging attempts were found based on the reduction of click intervals from about 100. ms to 2-3. ms, which suggests a prey capture attempt. We found 19 punitive prey capture attempts and of these 53% occurred at the maximum dive depth. This suggests that more than half of the possible prey capture events occurred at or near the sea bed. © 2012 Elsevier Ltd.


Lin T.-H.,National Taiwan University | Akamatsu T.,Japan National Research Institute of Fisheries Engineering | Akamatsu T.,Japan Science and Technology Agency | Chou L.-S.,National Taiwan University
Marine Biology | Year: 2013

This paper offers the first study of diurnal variations in the use of an estuarine habitat by Indo-Pacific humpback dolphins. Passive acoustic data loggers were deployed in the Xin Huwei River Estuary, Western Taiwan, from July 2009 to December 2010, to collect biosonar clicks. Acoustic encounter rates of humpback dolphins on the riverside of the estuary changed significantly over the four tidal phases, instead of the two diurnal phases based on the recordings from 268 days. Among the tidal phases, the encounter rates were lowest during ebb tides. Additionally, circling movements associated with the hunt for epipelagic fish significantly changed in temporal and spatial presence over the four tidal phases, matching the overall pattern of encounter rate changes in the focal estuary. Our findings suggest that the occurrence pattern and habitat utilization of humpback dolphins are likely to be influenced by the tidal-driven activity of their epipelagic prey. © 2013 Springer-Verlag Berlin Heidelberg.


Akamatsu T.,Japan National Research Institute of Fisheries Engineering | Wang D.,CAS Wuhan Institute of Hydrobiology | Wang K.,CAS Wuhan Institute of Hydrobiology | Li S.,CAS Wuhan Institute of Hydrobiology | Dong S.,CAS Wuhan Institute of Hydrobiology
Journal of Experimental Biology | Year: 2010

Dolphins and porpoises have excellent biosonar ability, which they use for navigation, ranging and foraging. However, the role of biosonar in free-ranging small cetaceans has not been fully investigated. The biosonar behaviour and body movements of 15 freeranging finless porpoises (Neophocaena phocaenoides) were observed using electronic tags attached to the animals. The porpoises often rotated their bodies more than 60 deg., on average, around the body axis in a dive bout. This behaviour occupied 31% of the dive duration during 186 h of effective observation time. Rolling dives were associated with extensive searching effort, and 23% of the rolling dive time was phonated, almost twice the phonation ratio of upright dives. Porpoises used short inter-click interval sonar 4.3 times more frequently during rolling dives than during upright dives. Sudden speed drops, which indicated that an individual turned around, occurred 4.5 times more frequently during rolling dives than during upright dives. Together, these data suggest that the porpoises searched extensively for targets and rolled their bodies to enlarge the search area by changing the narrow beam axis of the biosonar. Once a possible target was detected, porpoises frequently produced short-range sonar sounds. Continuous searching for prey and frequent capture trials appeared to occur during rolling dives of finless porpoises. In contrast, head movements ranging ±2cm, which can also change the beam axis, were regularly observed during both dives. Head movements might assist in instant assessment of the arbitrary direction by changing the beam axis rather than prey searching and pursuit.


Sudo H.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Kajihara N.,Japan National Research Institute of Fisheries And Environment of Inland Sea | Noguchi M.,Japan National Research Institute of Fisheries Engineering
Marine Biology | Year: 2011

Although mysids play important roles in marine food chains, studies on their production are scarce, especially for warm-water species. We investigated life history and production of Orientomysis robusta in a shallow warm-temperate habitat of the Sea of Japan. Its spawning and recruitment occurred throughout the year; 19 overlapping cohorts were recognizable over an annual cycle. The summer cohorts recruited in July-September exhibited rapid growth, early maturity, small brood size, and small body size. A converse set of life history traits characterized the autumn-winter cohorts recruited in October-March. The spring cohorts recruited in April-June had intermediate characteristics of both cohorts. Life spans were 19-33, 21-48, and 69-138 days for summer, spring, and autumn-winter cohorts, respectively, and mortality rates were high for spring and summer cohorts, especially during June-August but were low for autumn-winter cohorts. Production calculated from the summation of growth increments was 488.8 mg DW m-2 year-1 with an annual P/B ratio of 21.26. The short life span seems to be responsible for such an extremely high P/B ratio. A method not requiring recognition and tracking cohorts gave similar values (534.0 mg DW m-2 year-1 and 20.49). The close agreement in production values between the two methods indicates our estimates are valid. © 2011 Springer-Verlag.


Kawamata S.,Japan National Research Institute of Fisheries Engineering
Journal of Experimental Biology | Year: 2012

Algal mats can hinder the adhesion of the tube feet of sea urchins. This leads to the hypothesis that the restriction of sea urchin feeding activity by wave action can potentially be enhanced by the presence of algal mats, which will facilitate the survival of kelp recruits at sites with wave action in urchin barrens. To evaluate the potential anti-attachment effect of algal mats on sea urchins, a laboratory tank experiment was performed on the movement of Strongylocentrotus nudus sea urchins and their grazing on juvenile kelp plants at the center of 30×30 cm flat test substrates with or without a thin-layer microalgal mat at four levels of oscillatory flow (maximum orbital velocity: 10, 20, 30 and 40 cm s -1). The grazing loss of kelp slightly increased with increasing velocity up to 30 cm s -1 in the absence of microalgal mats, while in contrast the loss substantially decreased at 30 cm s -1 in their presence. Sea urchins were dislodged more frequently at 20 cm s -1 or higher velocities in the presence of microalgal mats. Mats were frequently abraded by scraping by the adoral spines during urchin movement at high velocities (30 and 40 cm s -1) but were subject to no or only slight urchin grazing in most cases. The results indicate that the overall decrease in grazing loss of kelp within the microalgal mats was attributable to the anti-attachment effect on urchins during incursions rather than due to urchins grazing on the mats. © 2012. Published by The Company of Biologists Ltd.


Hasegawa E.I.,Japan National Research Institute of Fisheries Engineering
Journal of Fish Biology | Year: 2012

The swimming depth of chum salmon Oncorhynchus keta equipped with archival tags was investigated off the Pacific Ocean coast of Hokkaido and North Honshu, Japan. As shown from movements of the fish with disc tags, O. keta swam at shallower depths during the full-moon phase than in the other phases and their swimming speed during this phase was faster compared to other phases. In addition, the circadian rhythm suggests a biological clock. These observations are all consistent with the view that O. keta make use of moonlight in order to navigate at night-time during homeward migration. © 2012 The Author. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.


Sugimatsu K.,Japan National Research Institute of Fisheries Engineering | Isobe A.,Ehime University
Journal of Oceanography | Year: 2011

From 1980 to 1995, in August, the bottom layer of Osaka Bay was occupied by cold, nutrient-rich water compared with that observed during both previous and subsequent decades. To investigate the mechanisms for the intrusion of bottom-layer cold water into Osaka Bay, the intrusion into Osaka Bay via the Kii Channel is simulated using a finite-volume coastal ocean model with unstructured triangular cell grids. The initial conditions, boundary conditions, and surface temperature given to the model are obtained from daily reanalysis data provided by the Japan Coastal Ocean Predictability Experiment. The model shows that cold water uplifted on the eastern side of the Kii Peninsula is propagated westward at 1.0 m/s as a coastal boundary current; it reaches the Kii Channel mouth when the Kuroshio axis is located around 74 km south of Cape Shionomisaki. However, the modeled cold water mass at the Kii Channel mouth does not intrude further to the north of the Kii Channel; therefore, another mechanism is required to explain the cold-water intrusion into the bottom layer of Osaka Bay. A plausible explanation is the estuarine circulation established by the freshwater supply at the bay head. When the river runoff is included in the model without forced vertical mixing, the temperature in Osaka Bay decreases 6.6 days later than the temperature decreases at the Kii Channel mouth. Furthermore, the shoreward current speed in the bottom layer of the modeled estuarine circulation is 15 cm/s, which provides the mechanism required for the cold water mass to pass the Kii Channel. © 2011 The Oceanographic Society of Japan and Springer.


Yasuma H.,Hokkaido University | Sawada K.,Japan National Research Institute of Fisheries Engineering | Takao Y.,Japan National Research Institute of Fisheries Engineering | Miyashita K.,Hokkaido University | Aoki I.,University of Tokyo
ICES Journal of Marine Science | Year: 2010

We report theoretical values of the target strength (TS) of four myctophid fish (Ceratoscopelus warmingii, Myctophum asperum, Diaphus garmani, and Diaphus chrysorhynchus) based on morphometry of the swimbladder. None of the D. chrysorhynchus had an inflated swimbladder, but the other species had both inflated and non-inflated swimbladders, depending on body size. The relationships between swimbladder and body length showed that once gas production started, the swimbladders grew faster than the rest of the body (positive allometric growth). However, M. asperum showed regression of the swimbladder after positive allometric growth, so larger specimens had non-inflated swimbladders. Based on the measurements of swimbladder and body length, the theoretical TS values at 38 and 120 kHz were calculated using existing sound-scattering models. In fish with inflated swimbladders, TS values were relatively low (less than -67 dB, reduced TScm) at both frequencies. Regression slopes on TS-body length (log) plots were >20, suggesting that their scattering cross sections were not proportional to the square of the body length. In contrast, the TS values of M. asperum decreased with growth in large fish (60-80 mm long) through swimbladder regression. Scattering cross sections of fish without swimbladders were not proportional to the square of the body length over the whole size range. © 2009 International Council for the Exploration of the Sea.


Terada D.,Japan National Research Institute of Fisheries Engineering | Matsuda A.,Japan National Research Institute of Fisheries Engineering
Proceedings of the International Offshore and Polar Engineering Conference | Year: 2011

In this study, a new technique to estimate directional wave spectra with respect to encounter waves of ships based on ship motions data is introduced. Firstly, the ship motion is analyzed by a Time Varying AutoRegressive modeling procedure, and cross spectra of the ship motion data is obtained. And then, based on the estimated instantaneous cross spectra, directional wave spectra with respect to the encounter wave are estimated by a state-space modeling procedure every time step. The proposed method is verified by numerical experiments. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).

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