FISHERY BULLETIN: VOL. 76, NO. 2 



7>\ 



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D 



Figure l. — Lobster traps having a rectangular vent positioned vertically (A) and horizontally (C) and single (B) and paired (D) circulai 



vents. 



Boothbay Harbor, Maine, with: 1) circular [58-mm 

 (2.3 in) and 61-mm (2.4 in) diameter] vents; 2) 

 vertical and horizontal rectangular [44.5 mm ( 1.8 

 in) X 152.4 mm (6.0 in)] vents; and 3) traps with- 

 out vents. Carapace length of lobsters was mea- 

 sured from posterodorsal edge of eye socket to 

 posterior margin of carapace and carapace width 

 (CW) of crabs, distance between the two m^ost pos- 

 terior notches on the anterolateral border of the 

 carapace, to the nearest millimeter. 



Trap escapement was studied by placing 

 lobsters of known sizes in traps with circular open- 

 ings of 58, 60, and 61 mm in diameter. Side en- 

 trances of each trap were closed so escapement had 

 to be via the vents. Traps were secured to the 

 laboratory dock and usually checked daily for es- 

 capement for about a week. 



To determine whether or not a crab or lobster 

 could pass through a round opening of a given size, 

 we correlated carapace length of lobsters with 

 carapace height (CH), and the carapace width of 

 crabs with carapace length . For 2 1 7 lobsters ( sexes 



combined), ranging from 70 to 98 mm CL, 

 carapace height was determined by positioning 

 the lobster's ventral surface on a flat board and 

 then measuring the greatest perpendicular dis- 

 tance from the board to the top of the carapace. 

 Carapace length of crabs was measured from the 

 anterior margin of the frontal region to the poste- 

 rior border of the intestinal region. Measurements 

 for the two Cancer species were treated separately 

 due to the species disparities in body shapes. We 

 recorded carapace length for 103 male rock crabs 

 (females were excluded due to commercial unim- 

 portance) ranging from 90 to 122 mm CW, and 96 

 Jonah crabs (sexes combined) ranging from 96 to 

 132 mm CW. 



RESULTS AND DISCUSSION 



Lobsters in Research Gear 



There are marked differences in size composi- 

 tion and number of lobsters caught in nonvented 



426 



