网目缩结对盘锦海域桁杆虾拖网网囊的选择性影响

为研究盘锦海域桁杆虾拖网网囊结构的调整,掌握网囊网目在不同缩结系数0.99、0.95、0.91时对桁杆虾拖网捕获葛氏长臂虾Palaemon gravieri和脊尾白虾Palaemon carinicauda的选择性影响,采用套网法对不同缩结系数的网囊网目进行了选择性试验。结果表明:随着网囊网目缩结系数的减小,两种虾的选择性曲线向右偏移,较小体长范围内虾的选择率变小,说明可以释放一定数量的幼虾;但当所捕获的葛氏长臂虾和脊尾白虾体长达到某一值时,缩结系数的减小对两种虾的选择性已无明显影响,当缩结系数为0.95、0.91时,对应葛氏长臂虾体长分别为42.5、52.5 mm,对应脊尾白虾体长均为47.5 mm。研究表明,缩结系数降低后,两种虾的选择范围均变小,选择性尖锐度变强,本研究结果可为桁杆拖网过渡期的合理利用和保护渤海海域幼虾类资源提供科学依据,也可为过渡期后的桁杆虾拖网归属问题提供一些理论参考。

Selectivity influence of change in mesh hanging ratio on cod-end of beam shrimp trawl in coastal area of Panjin,Liaoning Province

The influence of cod-end mesh hanging ratio at 0.99,0.95,and 0.91 on selectivity of shrimp Palaemon gravieri and Palaemon carinicauda was studied to regulate the cod-end structure of beam shrimp trawl in Panjin coastal area. The result showed that selective curve of two shrimp species was moved to the right,lower selectivity ratio for smaller shrimp with the decrease in cod-end mesh hanging ratio,indicating some juvenile shrimps escaped from the cod-end.However,no significant influence of hanging ratio on the selectivity of shrimp was observed when the two shrimp body length reached a certain value,captive Palaemon gravieri with body length of 42.5 mm at hang-ing ratio of 0.95;captive Palaemon gravieri with body length of 52.5 mm at hanging ratio of 0.91;and captive Pal-aemon carinicauda with body length of 47.5 mm at hanging ratio of 0.95 and 0.91. Selection range of two shrimp species was found to be decreased and the strength of selective sharp degree became strong as the hanging ratio de-creased according to the selective index. The findings provided some effective suggestions for protecting the juvenile shrimp resources and the rational use of beam shrimp trawl and some theoretical references for the affiliation prob-lem of beam shrimp trawl after the transitional period.