East China Sea Fisheries Research Institute,Chinese Academy of Fishery Sciences,Key and Open Laboratory of Marine and Estuarine Fisheries, Ministry of Agriculture,Shanghai 200090,China
Abstract: The selectivity tests of codend mesh in beam shrimp trawl were conducted in the entrance of Changjiang River by covered net method to evaluate the selectivities of three condend mesh size for shrimp Cargon affinis,Palaemon gravieri and conventional shrimps.The results showed that the shrimp Cargon affinis had 50%escapable body length(L0.5)of 41.36 mm at the codend mesh size of 20 mm,46.42 mm at the codend mesh size of 25 mm, and 57.68 mm at the codend mesh size of 35 mm.In Palaemon gravieri,the 50%escapable body length(L0.5) was 43.35 mm at the mesh size of 20 mm,47.20 mm at the mesh size of 25 mm,and 62.01 mm at the mesh size of 35 mm.The 50%escapable body length(L0.5)of the conventional shrimps were found 47.45 mm at the mesh size of 20 mm,50.56 mm at the mesh size of 25 mm,and 64.87 mm at the mesh size of 35 mm.The relationship between 50%escapable shrimp body length(L0.5)and mesh size(Me)is expressed as:Cargon affinis:L0.5= 1.0964Me+19.179,R2=0.9984;Palaemon gravieri:L0.5=1.2779Me+16.777,R2=0.9814;The conventional shrimp:L0.5=1.999Me+22.297,R2=0.9729.
2011, Vol. 26 
