FISHERY BULLETIN: VOL. 77, NO 1 



per trap haul (ClTH) tended to increase slightly 

 with increasing soak time in both vented and con- 

 trol traps up to 6 days when a slight decline be- 

 came evident (Figure 1). 



A different pattern emerged for the catch of sub- 

 legal lobster per trap haul ( C^TH ) where we noted 

 an initial increase in CgTH in nonvented traps 

 followed by a general decline with increasing soak 

 time. In vented traps, CgTH declined initially fol- 

 lowed by a slight increase with time (Figure 1). 

 The decline in CgTH in control traps with immer- 

 sion times in excess of 2 days may be the result of 

 escapement through the trap heads and mortality 

 within the trap (Bennett 1974; Austin 1977). We 

 attributed the immediate decline in CgTH in 

 vented traps to escapement, indicating the effec- 

 tiveness of the vents. It is unclear whether the 

 increase in CgTH for the sixth set over day was due 

 to sampling bias or some other factor. Bennett 

 ascribed catch increases with long soak times to 

 decay of the bait with an associated renewed re- 

 lease of chemical attractants. 



The catch of legal and sublegal lobster was not 

 proportional to immersion time. This may be due 



LEGAL 

 LOBSTER 



to the combined effects of declining local availabil- 

 ity, trap saturation, escapement, and mortality 

 (Bennett 1974; Austin 1977; Skud see footnote 3; 

 Bennett and Brown^). Catch per trap haul/set over 

 day (CTHSOD) declined with time in both vented 

 £md control traps (Figure 2). Similar observations 

 of declining CTHSOD with increasing soak time 

 have been noted in the Maine lobster fishery 

 (Thomas 1973), the spiny lobster fishery (Austin 

 1977) and the European lobster fishery (Bennett 

 1974). 



Our data indicated that CTH approached an 

 asymptote with increasing soak time for both legal 

 and sublegal lobster. Following the approach of 

 Sinoda and Kobayasi (1969) and Munro (1974) 

 this relationship may be modelled as: 



C, = CJl - exp{-Rs)) 



'Bennett, D.B., and C.G.Brown. 1976 The problems of pot 

 immersion time in recording and analysing catch-effort data 

 from a trap fishery. Int. Cons. Explor. Mer, Special meeting on 

 population assessment of shellfish stocks, No. 6, 8 p. 



LEGAL 

 LOBSTER 



~1 I 



1 2 



O vented 

 • Control 



3 4 5 



SET OVER DAYS 



Figure l — Relationship between catch per trap haul of Ameri- 

 can lobster euid trap immersion time in vented and control traps. 

 Legal lobster are s78 mm CL. 



O Vented 

 • Control 



SUBLEGAL 

 LOBSTER 



SET OVER DAYS 



Figure 2.— The relationship between catch per trap haul/set 

 over day of American lobster and trap immersion time in vented 

 and control traps. 



928 



