A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position.
In order to realize the utilization of cement-based materials in the special extreme environment, the deep sea, the authors have launched a project targeted at creating a technology platform with in-situ methods and systems for monitoring and evaluating cement-based materials located at deep ocean bottom sites. The first in-situ test in the world with a view to investigating the time-dependence of the volumetric stability and microstructure of Portland cement mortar following its long-term exposure to deep-sea conditions is currently underway at a 3515-m depth in the Nankai Trough. This paper reviews previous studies about the influences of deep-sea hydraulic pressure on cement-based materials, verifies the action of short-term hydraulic pressure using Portland cement mortars on a laboratory scale, and introduces the ongoing progress of in-situ deep-sea tests. Results from laboratory tests indicate that dimensional changes were provoked by liquid water infiltration and confinement while under short-term hydraulic pressure, however, time-dependent behavior under stresses such as creep has not appeared. Weight gain, changes in pore-size distribution, compressive strength and bending strength of the cement mortar were monitored after pressurization and depressurization processes.
JAMSTEC developed the new profiling float “Deep NINJA” for deep-sea type, was subjected to long-term monitoring of one year in the Antarctic Ocean off the coast of Adelie Coast from 2012. As a result, succeeded in the long-term monitoring of the sound speed profile to depth of the 4000 m in the Antarctic Ocean for the first time in the world, and was able to capture a seasonal change in the surface area in the freezing season and the thawing season. In addition, calculating a sound speed from these data, simulations were performed assuming the low frequency sonar. The result was obtained, the ingredient which propagates while repeating a reflection in the extremely small layer of the sea surface neighborhood, and the ingredient that propagates while being reflected in near the water depth 100m which changes of sound speed gradient. From this, propagation loss was small in winter than summer, and was shown a possibility that a sound wave would propagate to a more distant place. This may affect the long-distance sound wave propagation of the echo locations of the passive sonar and marine mammals.
Abstract:Japan is a small island country surrounded by a vast EEZ which is thought to contain rich offshore resources, such as oil and natural gas. Recently, seismic surveys have been carried out to locate such resources. Because of their high resolution, seismic surveys are predicted to increase in the future.However, these surveys utilize air guns, which generate intense and low-frequency impulse noises known to disturb and harm marine mammals. The impact of seismic survey noise on marine mammals began to attract attention in the early 1970s, and acoustic impact thresholds and mitigation measures are still discussed all over the world. Here we propose an assessment method utilizing ARGO data and ocean-bottom topography data from Google Earth. We studied influences by seasonal climate changes and ocean-bottom topography with respect to the results of impact assessment, and found that these gave meaningful differences to our assessment results. This finding suggests that our proposed method is adequate for assessing the impact of seismic survey noise on marine mammals. We also assessed received levels of noises generated by air guns in a cetacean habitat near the Ogasawara Islands, utilizing the proposed method and the newest acoustic impact thresholds as updated in March 2016 by NOAA.
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