Macroalgae occasionally flows into the water intakes of coastal industrial facilities, causing blockage. Therefore, we conducted a unit acreage sampling and a diving survey for macroalgae near a power plant on the coast of the Bohai Sea to investigate the dominant species and to clarify their temporal and spatial distributions. The dominant species were green algae; Enteromorpha linza, Ulva pertusa, brown algae; Sargassum thunbergia, Punctaria latifolia, and red algae Ceramium kondoi, Gelidium sp.. Green and brown algae accounted for about 80% of the total in the studied area. The Dazuizi (DZZ) area, where gravels and reefs are widely dispersed, was clarified to be the primary macroalgae habitat, with a biomass of 0.7 kg/m2 and a total weight of 837.1 t, which was about 20 times of the Jiangshidi (JSD) area. The significant increase in macroalgae began in May when the water temperature reached about 15°C and peaked around June. In July, the water temperature raised above 25°C; the macroalgae began to decline. From the GLM analysis, it was cleared that the biomass of green algae was affected remarkably by the environmental factors relative to the other algae.
Recently, some bottom trawl fisheries have begun targeting not only fish species that live on the continental shelf, but also those that live on the slope of the continental shelf. For ecosystem conservation and resource management, it is necessary to know catch performance of trawl gears for these species as well as biological characteristics of these species. Of catch performance, minimum body length of fish caught by trawl nets was basically restricted by codend mesh size. Thus, this study estimated codend selectivity curves for four fish species, deep-sea smelt Glossanodon semifasciatus, rosefish Helicolenus hilgendorfi, blackmouth splitfin Synagrops japonicus, and silverbelly seaperch Malakichthys wakiyae by using SELECT analysis, based on data from trouser trawl experiments carried out on the continental slope of the East China Sea with a test codend of 60 mm diamond mesh (54 mm mesh opening) and a control codend of 9 mm bar length square mesh. As a result, fish with body girth larger than mesh perimeter of 10.8 cm corresponding to twice of the mesh opening are unable to pass through the mesh of the codend. This suggests that the estimated codend selectivity is due to an effect of the codend mesh.
The 2022 JSFE Fall Symposium “Thinking about future aquaculture facilities Marine Visualization Using Underwater Drones (Low-cost Version, Wired)” was held in October 2022. The number of participants was about 120. The features of underwater drones, which have been remarkably developed recently, were introduced, as well as several examples of them. This paper is made of the seven lecture outlines that have summarized by symposium combiners.
The global environment has changed dramatically in the last ten years. Southern fishes were moving north due to the rise in seawater temperature associated with global warming. Changes are occurring in all marine life, not just fish, but also crustaceans and cephalopods. Apart from the problem of global warming, marine debris is harming marine life. 2020, the coronavirus (COVID-19) has spread, and the number of anglers at outdoor sea fishing parks has increased rapidly. As a result, it accelerated the increase of new marine debris. Unlike divers who follow rules and manners, only the fishing leisure industry, which does not take measures, enjoys its benefits.
I have been a diver for 40 years and am in a position to fish. There is a problem in the social structure that gives priority to the short-term economic activities of human beings by directly feeling the habitat changes of fish species. These human activities may be causing environmental changes. I’m not an environmental expert. However, I want to pass on the rich nature of the sea to the children who will live in the future, so I am doing what I can as an individual. It is the use of small underwater drones that are cheap and small enough to be carried by individuals. In order to visualize the sea fishing park and let many people know the current state of the sea, we are using SNS and spreading it under the name of “Negakari Project”. Furthermore, as a countermeasure, we have created a “guide map for obstacles that catch fishing lines.” I would like to expand this activity nationwide.
Recently, the underwater drone has been developed and utilized in industry. In this paper, we introduce current situation of the utilization of underwater drone in industry and discuss advantages and disadvantages of using underwater drone comparing with diving with scuba. The underwater drone is used in oceanic and freshwater survey, safety inspection of infrastructures, life-saving services, and fisheries. Utilization of the underwater drone in these situations is able to reduce hazardous tasks and employment cost of divers. In the survey of water distinct, the underwater drone can also survey deeper zone (over 30-m depth) during longer time than diving observation even though scuba diving needs countermeasures against the decompression disease. On the other hand, diving observation can observe the object more precisely than underwater drone. Particularly, in survey of seaweed bed, diving observation can distinguish much more variety of organism species. We introduce the case of utilization of underwater drone for the analysis of coverage survey of seaweed bed. Images of seaweed bed taken by an underwater drone were used for obtaining the teaching and validating data for distinguishing seaweed bed from satellite images. The accuracy of the identification method of seaweed species from the images were applicable for practical situation but need more improvement.
A method for inspecting aquaculture facilities was examined using a small and lightweight underwater drone.
Demonstration experiments were conducted in yellowtail aquaculture cages and scallop and sea squirt aquaculture facilities, and the results were compiled into guidelines. A method for inspecting aquaculture facilities was examined using a small and lightweight underwater drone. Demonstration experiments were conducted in yellowtail aquaculture cages and scallop and sea squirt aquaculture facilities, and the results were compiled into guidelines.
Since inspections of fishing port facilities must be carried out on a regular and temporary basis, the burden on fishing port managers is heavy, and efficiency must be improved. This paper introduces the applicability to inspection of underwater fishing port facilities using ROV.