Abstract:Far-reaching mariculture is an important way to relieve the pressure on the ecological environment of coastal waters, expand new space for mariculture in China, optimize the layout of the marine fishery industry, and promote the green and high-quality development of aquaculture. In recent years, moving the islands and reefs far away from the continental coastline as the early development sea area and the equipment-first behavior as the development characteristics of deep-sea aquaculture, China´s far-reaching mariculture has been preliminarily developed. Combined with China´s sea areas, sea conditions, breeding varieties, and market demand, the independent and innovative large-scale engineering fence facility breeding model of Pseudosciaena crocea has been successful. In order to evaluate the sediment status in the sea area of the large-scale fenced large yellow croaker (Larimichthys crocea) in the deep-sea, the regional distribution, content change, and pollution level of Cu, Zn, organic carbon, sulfide and other indicators in the sediments of the surveyed sea area were analyzed. These parameters were evaluated through four investigations in the fenced culture area, peripheral area of the fence, peripheral area of the cage, and control area of L. crocea, in different culture periods, and the Nemerow index was used to comprehensively evaluate the quality of sediments in the surveyed sea area. The results showed that the Cu content in the sediments varied from 15~33 mg/kg; the Zn content varied from 80~137 mg/kg; the organic carbon content varied from 0.14%~1.90%; and the sulfide content varied from 0.3~128.0 mg/kg. The contents of organic carbon and sulfide in the sediments in the fenced culture area were higher than those in other areas, however, they all met the first class of marine sediment quality standards (GB18668-2002). There was no significant difference in the contents of Cu, Zn, and organic carbon in the sediments of the different investigation areas (P>0.05), and the content of sulfide in the sediments of the breeding area in the fence center was significantly higher than that in the control area (P<0.05). In this study, the Nemerow index comprehensive analysis revealed that the sediment quality of all sampling stations during the survey was of clean (classⅠ) or relatively clean (classⅡ) status, and the sediment quality of each station maintained a stable and good level during the survey time. On one hand, high breeding density is not an issue in the sea area, and the breeding layout is more scientific and reasonable, but good water exchange in the sea area can dilute and diffuse some pollutants, such as residual bait and feces; on the other hand, the deep-water network in the sea area generally occurs around December every year. Therefore, the large yellow croaker cultured in boxes and fences could be caught and sold. The large yellow croaker species can be re-invested around May of the next year. Thus, the sea area has several months for renewal of its resources in the non-breeding period. No obvious accumulation trend of Cu, Zn, and sulfide in the sediments was observed, but a slight accumulation trend of organic carbon in the sediments was observed during the study period. The research and development, and application of formula feed for the large yellow croaker should be enhanced to alleviate the current large-scale investment of frozen fish bait and reduce the bait coefficient, thus reducing the pollution of organic matter accumulation in the sedimentary environment to a certain extent. According to the breeding cycle of large-scale fenced L. crocea in the far-reaching sea, this study monitors the key characteristics and sedimentary environmental factors in the fenced breeding area and the surrounding sea areas. It comprehensively evaluates the current situation of sediment quality in order to have a basic understanding of the current situation of pollutants in large-scale fenced breeding. The results provide a basis for rational planning of the large-scale fenced breeding areas in the far-reaching sea and provide data support for disease control and sustainable development of mariculture.
