FISHERY BULLETIN: VOL 76, NO. 2 



Table 2. — Comparison of commercial catches of sublegal and 

 legal-sized lobsters caught in traps with 58-mm circular vents and 

 traps without vents. 



Trap type 



Side vent: 



double opening 

 No vent 

 End vent: 



single opening 

 No vent 



No. of 

 sublegals; 

 trap haul 



98 

 233 



1.80 

 2.76 



No. of 



legals/ 

 trap haul 



56 

 49 



72 

 057 



No of 

 trap 

 hauls 



144 

 132 



144 

 144 



Sublegals: 

 legals 



1.8:1 

 47:1 



25 1 

 4.9:1 



HORIZONTAL VENT 

 n =124 

 X = 91.2 

 SE = 89 



60 70 80 90 100 IIC 120 



Possible explanations for these disparities in ef- 

 ficiency may be that: 1) larger lobsters are less 

 likely to enter traps containing several other 

 lobsters, and/or 2) after legal lobsters are caught, 

 their attempts to escape might be intensified as 

 the density of lobsters increases w^ithin the trap. 

 Aside from the previously mentioned differ- 

 ences in the number of shorts caught per trap haul 

 for vented and nonvented traps, end vents (single 

 hole) captured 1.80 shorts/trap haul, whereas side 

 vents (double hole) caught only 0.98 shorts/trap 

 haul (Mest, P<0.01). Apparently, the additional 

 vent will insure greater escapement. 



Crabs in Research Gear 



Since male C. irroratus attain larger sizes than 

 females (Krouse 1972), commercial catches of this 

 species are comprised almost entirely of males, so 

 in the following analyses only catches of male 

 crabs are considered. Variations in size composi- 

 tion of catches with different vents as manifested 

 by width-frequency histograms (Figure 3) and 

 mean carapace widths which are statistically dif- 

 ferent ( Duncan's new multiple range test, P <0.01 ) 

 indicate that: 1) fewer large crabs ( ^90 mm CW) 

 were captured in traps with horizontal vents 

 (mean 91.2 mm CW); and 2) as many, if not more, 

 larger crabs were collected with circular (mean 

 96.5 mm CW) than nonvented traps (mean 93.8 

 mm CW). According to this data, the 58-mm circu- 

 lar vent is at least as efficient in retaining 

 marketable-sized crabs as the nonvented trap and 

 certainly much more efficient than the horizontal 

 vent. Escapement of subcommercial-sized crabs 

 through circular openings has long been recog- 

 nized by west coast States with Dungeness crab 

 fisheries (Miller 1976). These states require crab 

 traps to have one or two escape rings with diame- 

 ters &4 in. 



This situation was further evaluated by compar- 

 ing the numbers ( crabs ^90 mm CW) per trap haul 



428 



35 

 30 

 25 



UJ 



D 



O 20 



Ld 



(T 15 



Ll- 



10 



t- 



Z 5 



UJ 



O 



cr 



35 

 30 

 25 

 20 

 15 

 10 

 5 

 



60 70 



80 



5R mm CIRCULAR VENT 

 n =93 

 7 " 96.5 

 SE = 0.66 



60 70 80 90 100 110 120 



CARAPACE WIDTH (mm) 



Figure 3. — Width-frequency distributions for male rock crabs 

 caught with nonvented traps, traps with 58-mm circular vents, 

 and traps with horizontal vents fished near Boothbay Harbor, 

 Maine. 



set over day for each of the different vents (Figure 

 4). CPUE values were highest for circular vents, 

 lowest for horizontal vents, and intermediate for 

 vertical and nonvented traps. Thus circular vents 

 relative to the other vents were most effective in 

 retaining crabs 3^90 mm CW and based on the 

 following ratios of nonkeepers ( <90 mm CW) to 

 keepers (^90 mm CW), selectively fished for 

 larger crabs: 



Vent type 



Circular Nonvented Horizontal Vertical 

 Nonkeepersikeepers 1.5:1 2.5:1 4.1:1 5.7:1 



Even though smaller crabs can egress quite read- 

 ily from traps with horizontal and vertical vents, 

 the above values at first glance appear to reflect 

 the converse, i.e., more nonkeepers are caught in 



