FOGARTY and BORDEN EFFECTS OF TRAP VENTING ON GEAR SELECTIVITY 



openings or control traps (Table 5). The sublegal 

 catch was substantially reduced in comparisons of 

 traps with 42 mm escapement openings and con- 

 trol traps (Table 5). Contingency table analyses 

 indicated that the catch characteristics of each 

 vented trap type were significantly different from 

 control traps (Table 5). Traps with horizontal 

 vents (both size classes) tended to catch fewer 

 legal-sized lobster than control traps (Table 5 ). We 

 were unable to offer a direct explanation for this 

 observation since, based on morphometric studies 

 and laboratory observations, escapement of lob- 

 ster s=78 mm CL through 42 mm vents would be 

 impossible and escapement of legal-sized lobster 

 through 44.5 mm vents would be minimal. The 

 effect of vent orientation on the sublegal catch was 

 negligible. Krouse ( 1978) found no significant dif- 

 ferences in the catch characteristics of traps 

 equipped with horizontal and vertical vents. 



Traps with increased lath spacing tended to re- 

 tain more sublegals than traps equipped with 

 equivalent-sized vents (Table 5) suggesting that 

 synthetic vents were more efficient escapement 

 devices. In this experiment the opened lath spac- 

 ing was oriented vertically in the end panel of the 

 parlor section of the trap. Although the vent width 

 determines the selection characteristics of the 

 trap, the length and orientation of the vent (or lath 

 spacing) may directly affect the probability of 

 locating the opening. Vertically positioned escape 

 openings offer a target equal to the width of the 

 opening, a relatively small area while horizon- 

 tally positioned vents proffer a much larger target. 

 Laboratory observations indicated that escape- 

 ment openings were located by an apparently ran- 

 dom search process, suggesting that larger target 

 areas will be located more quickly and efficiently. 



The catch of legal-sized lobster tended to in- 

 crease slightly or remain constant with increasing 

 soak time for each trap type with the exception of 



control traps, which demonstrated a decline as 

 immersion time increased (Figures 5, 6). The catch 

 of sublegal lobster remained consistently low with 

 increasing soak time in traps with 44.5 mm es- 

 capement openings while that for traps with 42 

 mm openings exhibited considerable variability 

 (Figures 5, 6). 



^-< 



LEGAL 

 LOBSTER 



A Horizonta I Vent 

 O Vertical Vent 

 ■Lath Space 

 " -, A Control 



SUBLEGAL 

 LOBSTER 



1 2 3 



SET OVER DAYS 



Figure 5. — Relationship between catch per trap haul of Ameri- 

 can lobster and trap immersion time in 42 mm vertical vented, 

 42 mm horizontal vented, 42 mm lath spaced, and control traps. 



Table 5. — Number of legal (^78 mm CL), sublegal, and percentage of legal American lobster; and ratio of sublegal to legal lobsters 

 (S/L) and catch per unit effort in experimental traps. CTH and CTHSOD denote catch per trap haul and catch per trap haul/set over day, 

 respectively. The subscripts Lands indicate the catch of legal and sublegal lobster. The abbreviations V,H, and L refer to vertical and 

 horizontal vent orientation and lath spacing. Numbers in parentheses are totals adjusted to retain equal sample sizes. Chi-square 

 contingency table analyses compared the catch characteristics of control traps with each individual trap type. 



"P .0.005. 



931 



