Some species of deep-sea cold-water corals and sponges provide complex habitats for other species and comprise unique ecosystems. Such ecosystems are considered as vulnerable marine ecosystems (VMEs) since they are easily damaged by anthropogenic disturbances and require a long time for recovery. The destructive impacts of high-seas bottom fisheries on deep-sea VMEs have led to heated debate in the United Nations General Assembly, and fisheries management bodies are required to avoid the significant adverse impacts (SAIs) of bottom fishing on VMEs in their areas of competency. Accordingly, fishing nations and regional fisheries management organizations introduced measures for the conservation and management of VMEs by distinguishing existing fishing areas and unfished areas, closing the unfished areas to commercial fishing operations, and introducing VME encounter protocols and VME closures. Such frameworks to assess and manage the impacts of bottom fishing on seafloor habitats are necessary in Japan for ensuring the conservation of marine biodiversity and the sustainability of fisheries.
To monitor the post-release movements of hatchery-reared Mekong giant catfish Pangasianodon gigas, 15 0-year-old fish tagged with acoustic transmitters were released into Kaeng Krachan reservoir, Thailand. Twenty automatic monitoring receivers were installed throughout the reservoir and tracked fish for a maximum of 252 days. Most of the fish moved throughout the reservoir for about 1 month and then came to utilize relatively small areas near the middle of the reservoir or near the dam. The radius of the daily habitat was about 1.4 km and the center of the daily habitat moved less than 500 m, indicating that the core areas were fixed within a small area. However, the distance traveled by eight fish monitored for more than 2 months sometimes exceeded 2 km per day. Six of the eight fish showed periodicity, with the transmitter signals detected only during the day or at night, indicating diel horizontal movements. All fish stopped their movements or all receivers ceased receiving signals before the battery lives of the transmitters expired, suggesting predation, bycatch, or transmitter shedding.
A major obstacle to rearing eel larvae is deterioration of water quality due to the use of slurry-type artificial food. Frequent feeding is necessary to ensure the growth and survival of larvae, while transferring the eel larvae to a new tank after feeding is stressful for both humans and larvae. We have invented a pipe-joined multi-tank system, in which rearing water is continuously supplied to the upstream tank and then flows into the downstream tank through the pipe. A pipe with an inner area of less than ~12 cm2 and a water flow faster than ~1 mm s−1 efficiently prevented the penetration of turbid water from the downstream tank to the upstream tank. By controlling the light environment, the larvae fed in the downstream tank could spontaneously move to the upstream tank through the pipe without penetration of turbid water from the downstream tank.
To prevent Maillard browning of the Japanese common squid Todarodes pacificus during air-drying, the effect of treatment with a saturated sodium citrate (Na-citrate) solution was investigated. The degree of browning of dried squid meat immersed in the Na-citrate solution before drying (Na-citrate meat) was significantly lower than that of dried untreated meat and the dried meat immersed in ion exchanged water before drying. Results of SDS-PAGE analysis revealed that myosin heavy chain degradation of the Na-citrate meat was suppressed during drying compared to other dried samples. The total amount of free amino acids in the Na-citrate meat was lower than that in the other dried samples. These results suggest that Na-citrate prevents the generation of free amino acids, which are involved in the Maillard reaction, and results in a lower degree of brown discoloration of dried squid.