Spatial and temporal distribution characteristics of sail-style 

stow net fisheries in Jiangsu Province

Abstract: In the early 1980s, the technical personnel of Qidong, Jiangsu Province, made improvement on the basis of Korean anglerfish nets and successfully developed sailstyle stow nets. Because of the large size of the main scale of stow net, the flexibility of fishing operation, high yield, low cost and good efficiency, it was quickly promoted. By the end of 1980s, Jiangsu developed 200300 sailstyle stow net fishing vessels, and in the early 1990s, it was introduced to Zhejiang, and by the end of the 20th century, the number of fishing vessels in the whole East China Sea area had grown to nearly 3 000. However, the small mesh and poor selectivity of the gear have caused serious damage to juvenile fish resources, which caused widespread concern among fisheries management and the public. In 1995, the Fishery Bureau of East China Sea Region formulated the "Implementation Measures for the Management of Sailstyle Stow Net Operation", which controlled the total number of fishing vessels, restricted the operation area and the number of nets, and implemented fishing moratorium, and the total number of fishing vessels should not exceed 1 000; in 2 000, the State Administration of Fishery and Port Supervision issued the “Interim Measures for the Management of Sailstyle Stow Net Operations”, which implemented the management principle of special permit, year by year reduction and final elimination of sailstyle stow net operations. After more than 10 years of control, although sailstyle stow nets have not withdrawn from the fishing industry, the number of fishing vessels has been effectively controlled and reduced, and the total number of fishing vessels in Jiangsu is now controlled in hundreds. Since the overall fisheries related to sailstyle stow net fishing vessels are less studied, this paper analyzes the daily production and catch structure and spatial and temporal distribution of fishing grounds based on a large number of random sampling survey data of sailstyle stow net fishing vessels along Jiangsu coast in 2014, to lay foundation for further research related to fishing grounds zoning and other related studies in the future, and also provide technical support for the formulation and implementation of related fisheries management measures. The results of this study show that the production waters of sailstyle stow net fishing vessels in Jiangsu Province are relatively concentrated in Dasha fishing ground, and the fishing grounds expand to the south, offshore or nearshore waters in individual months according to the changes of fishery resources. The water depth range is 3050m in relatively concentrated waters of fishing vessel distribution, and the proportion is more than 50%. The sailstyle stow net fishing area is located in the intersection of the Yellow Sea and the East China Sea, and belongs to the area where the “Yellow Sea cold water mass” and Kuroshio tributaries meet, and the water masses of different natures often mix, with frequent exchange between the upper and lower water layers, rich in nutrient salts and high primary productivity. The water depth gradient in the production waters of Jiangsu Province is relatively small, and the bottom is relatively flat; the substrate is the mud and sand of the radiating sandbar, which is suitable for anchoring and releasing the net by sailstyle stow net. The span of the fishing range in the eastwest direction and the northsouth direction shows a relationship between this and the other, that is, the distribution of fishing vessels expands in the eastwest direction (longitude range), then shortens in the northsouth direction (latitude range); and vice versa. This relationship may be due to a change in the distribution of fishing resources, which leads to a change in the operating waters of fishing vessels. The number of fishing areas covered by each month of operation is related to the production of fishing vessels, i.e., there is a significant negative correlation between the number of fishing areas and average CPUE. Stated differently, the higher the production, the more concentrated the fishing area is conversely, the higher the number of fishing areas covered by the operational area, the lower the average production. This relationship responds to the production strategy of fishermen, i.e., when yields are not high, fishing vessels spread out and try to expand their range to find new fishing grounds; once they find fish, they gather. There is a relatively stable central water area (Dasha fishery) for sailstyle stow net production; with the emergence of the main economic species in season, it will directly affect the changes in the distribution of operating waters. The composition of the catch changes somewhat with the season, and the spatial and temporal variation of resources of the main economic species is the main reason for the variation of sailstyle stow net fishery. In winter and spring, small pelagic fish, small shrimps and juvenile economic fish are the main targets of sailstyle stow nets; in autumn, economic fish species such as hairtail (Trichiurus haumela), small yellow croaker (Pseudosciaena Polyactis) and swimming crab (Portunus trituberculatus) are the main fishing targets. In comparison with historical literature, it is found that the main catch species of sailstyle stow nets are replaced by crustacean crabs with relatively lower nutritional class instead of common silvery pomfret, which shows that the composition of sailstyle stow nets has changed, reflecting a certain degree of change in the structure and function of the marine ecosystem. Although measures have been taken to eliminate sailstyle stow net fishery, because of the irreplaceable advantages of low cost and high efficiency, hundreds of fishing vessels are still in production in Jiangsu Province. In the present situation that sailstyle stow net operation can not be completely banned, consideration should be given to further strengthen the strict management of the mesh size of sac nets, strictly control the number of nets carried by fishing vessels, and minimize their fishing intensity, so as to effectively protect the growth and replenishment of juvenile economic fish and maintain the sustainable development of fisheries.

Keywords: sailstyle stow net; sampling survey; average daily production; catch composition; fishery distribution