FISHERY BULLETIN: VOL. 77. NO 4 



a 

 < 



A Hor I lontal Vent 

 O Vertical Vent 

  Latti Space 

 ' -^ ^ Conttol 



SUBLEGAL 

 LOBSTER 



SET OVER DAYS 



Figure 6. — Relationship between catch per trap haul of Ameri- 

 can lobster and trap immersion time in 44.5 mm vertical vented, 

 44.5 mm horizontal vented, 44.5 mm lath spaced, and control 

 traps. 



CONCLUSIONS 



The beneficial effects of incorporating escape 

 vents in standard lobster traps are well estab- 

 lished (Krouse and Thomas 1975; Krouse 1978; 

 Pecci et al. 1978). A reduction in lobster injury and 

 mortality and a reduction in onboard sorting time 

 are among the benefits accrued through the use of 

 escapement devices (Krouse and Thomas 1975; 

 Pecci et al. 1978). Lobster damage is related to the 

 effects of fishing activity both directly as a result of 

 handling (Scarratt 1973; Krouse 1976) and indi- 

 rectly as a result of aggressive encounters in the 

 trap (Pecci et al. 1978). Although interspecific ag- 

 gression levels £tre relatively low under natural 

 conditions (Cooper and Uzmann 1977), the arti- 

 ficially close confines of a trap may increase the 

 probability of aggressive behavior. 



The results of the present study confirm the 

 utility of employing escapement devices in lobster 



traps. We noted substantial reductions in the 

 catch of sublegal-sized lobster, reducing the prob- 

 ability of injury and mortality. Vented traps 

 tended to consistently capture more legal-sized 

 lobster than control traps. We attributed this in- 

 crease to an inverse relationship betweeen density 

 in the trap and the probability of new entries. 



This apparent increase in relative gear ef- 

 ficiency may have a significant impact on catch 

 rates if widely applied and should be closely moni- 

 tored. Given the critically high levels of fishing 

 mortality for lobster in virtually all sectors, this 

 increase in trap fishing power is presently inad- 

 visable. The use of 100% retention of legal-sized 

 lobster as the primary criterion for the establish- 

 ment of escape vent dimensions should therefore 

 be modified to allow for some minimal escapement 

 of legal lobster and to maximize escapement of 

 sublegal lobster. 



ACKNOWLEDGMENTS 



This research was made possible by a grant 

 through the Southern New England Fisheries De- 

 velopment Program, NOAA, under grant 03-6- 

 043-35132. We express our appreciation to the 

 fishermen who contributed to the successful com- 

 pletion of this study. We also wish to thank Bar- 

 bara Simon for computer programming and data 

 management and Linda Gray for typing the man- 

 uscript. J. Stanley Cobb, John Cronan, and John 

 Stolgitis reviewed the manuscript and offered 

 helpful suggestions. 



LITERATURE CITED 



AUSTIN, C. B. 



1977. Incorporating soak time into measurement of 

 fishing effort in trap fisheries. Fish. Bull., U.S. 75:213- 

 218. 

 Bennett, D. B. 



1974. The effects ofpot immersion time on catches of crabs. 

 Cancer pagurus L. and lobsters, Homarus gammarus 

 (L.). J. Cons. 35:332-336. 



Cobb. J. S. 



1971. The shelter-related behavior of the lobster, 

 Homarus americanus. Ecology 52:108-115. 



Cooper. R. a., .^nd J. R. Uzmann. 



1977. Ecology of juvenile and adult clawed lobsters, 

 Homarus amencanus, Homarus gammarus, and Neph- 

 rops Twrvegicus. In B F. Phillipsand J.S. Cobbleditors), 

 Workshop on lobster and rock lobster ecology and physiol- 

 ogy, p. 187-208. Aust. Div. Fish. Oceanogr., Circ. 7. 



Hartley, H. O. 



1961 . The modified Gauss-Newton method for the fitting of 

 non-linear regression functions by least squares. 

 Technometrics 3:269-280. 



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