Study Of Fishing Gear Selectivity Of Shrimp Trawl In The Yellow Sea

Selectivity of fishing gear, which means selected fishing capacity of objective species and the ability to prevent by-catch of unwanted species. It is the result of interaction between fishing gear and capture behavior.Study of selectivity of fishing gear have been widely used in many aspects, such as management of fishery resources, assessment of fisheries resource and separation at sea of products of catch and so on. Therefore, it is received increasingly special attention.Shrimp trawl fishery is a kind of single bottom trawl fisheries whose main feature is diversity in catch composition and the high rate of fish discarded in catch, is one of the most serious fishery in the world's bycatch and discards problems. Many selectivity experiments about different mesh configuration have been carried out in the East China Sea and the South China Sea. But the selectivity experiments, have not been conducted in the Yellow Sea. In order to analyze how the fishing gear in the shrimp fishery affect the size selectivity of the main catch and especially how the mesh configuration affect the selectivity of shrimp fishery in the Yellow Sea, it is necessary to have this sort of research.At present, in area of Shandong coastal waters in the Yellow Sea, shrimp trawl codend mesh size to catch Trachypenaeus Curvirostris is generally small, and some even as small as 17mm, so the composition of the catch has not reached economic maturity has been juvenile fish, with shrimp representing a large proportion, while the fish and shrimp juvenile has very low economic value, and what is more important is that a large number of juvenile death will inevitably cause a huge waste of fishery resources. For this problem, in 2007 and 2008 from September to November, near Shandong coastal waters in the Yellow Sea area, we carried out selectivity tests with sets the covered codend method for the 30mm,33mm and 40mm in the shrimp trawl codend. The results showed that:in the mesh size of 30mm,33mm and 40mim, the main choices of Trachypenaeus Curvirostris length L50 was 59.8mm,60.1mm and 63.2mm respectively, select range was 14.4mm,16.0mm and 22.9mm, and selectivity parameters with the increase of mesh size increases linearly. According to test results, that the present 33mm mesh size in codend for the Yellow Sea shrimp trawl fishery for shrimp in the release area can basically meet the requirement that the Yellow Sea shrimp trawl codend mesh size of the smallest should not be less than 33mm.The Yellow Sea shrimp trawl fishery has the complex catch object, except Trachypenaeus Curvirostris catched mainly, the economic juvenile fish and shrimp is also much, just by changing the mesh size is difficult to achieve the object of fishing gear selective fishing. Therefore, based on changing the codends mesh size, a further separate effect of separator panels of the shrimp trawl test was carried out. As the test take shrimp trawl as fishing gear, the forward part of the codends was installed with 40mm inclined separator panels (separator panels fixed by oval rigid frame.Thus, the codends was separated into the top codends (fish codends) and the bottom codends (shrimp codends) to Initial separate fish and shrimp. According to data of the catch, the retention of the main shrimp Trachypenaeus Curvirostris was calculated,and evaluated the separation effect.Meanwhile, the use of Logistic curve as a selective model get body length selectivity curve of the separator panels of the mesh size for the main shrimp.And the use of maximum likelihood estimation method estimates selectivity parameters and the main selective index of Trachypenaeus Curvirostris.The results showed that separator panels of 40mm have a good effect to release fish. But the effect of the main shrimp retention is not the best. meanwhile, the main selectivity index and Selectivity factor of Trachypenaeus Curvirostris for the 40mm mesh size codends is bigger than 40mm separator panelsWhether selectivity test of shrimp trawl codend mesh or experimental research of separator panels, this trial was not considered escape survival rate,and assumed that escape survival was100%.It is bound to overestimate ability of the fishery resources sustainable development. Therefore, in the future study, the escape ability and viability of fish and shrimp should be the index of a shrimp trawl net effect of a selective evaluation.