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

ZHUANG Xin;ZHANG Guo-sheng;LI Jing-yao;CHEN Shao-jun;WANG Zhen-yu;WANG Yi-ning;LIU Jing;XU Meng;JIANG Hong-zhe;XING Bin-bin;College of Marine Science and Environment,Dalian Ocean University;Center for Marine Ranching Engineering Science Research of Liaoning,Dalian Ocean University;China National Fisheries Corporation;College of Navigation and Ship Engineering,Dalian Ocean University;

Panjin coastal area;;beam shrimp trawl;;hanging ratio of cod-end mesh;;Palaemon gravieri;;Palaemon carinicauda

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 hanging ratio of 0.95; captive Palaemon gravieri with body length of 52.5 mm at hanging ratio of 0.91; and captive Palaemon 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 decreased 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 problem of beam shrimp trawl after the transitional period.