EFFECTS OF TRAP VENTING ON GEAR SELECTIVITY IN 



THE INSHORE RHODE ISLAND AMERICAN LOBSTER, 



HOMARUS AMERICANUS, FISHERY 



Michael J. Fogarty and David V. D. Borden' 



ABSTRACT 



The incorporation of escapement devices in lobster traps has proven effective in allowing the release of 

 sublegal -sized American lobster, Homarus americanus. and reducing the potential for trap related 

 iiyury and mortality. The present study was undertaken to assess the effects of trap venting on size 

 selectivity and catch per unit effort in the inshore Rhode Island lobster fishery. The use of rectangular 

 vents {42 x 152 mm) resulted in a 79^ decrease in the sublegal <78 mm carapace length) catch. Vented 

 traps tended to consistently catch greater numbers of legal-sized (3=78 mm carapace length) lobster, 

 possibly due to a density dependent effect. The mean size of lobster caught in vented gear was 

 significantly greater than in control traps. An analysis of the effect of trap immersion time indicated 

 that the catch is asymptotic with increasing soak time up to 7 set over days. 



Comparisons of the effectiveness of 42 ' 152 mm and 44.5 « 152 mm vents indicated that no 

 substantial loss of legal lobster would occur and that escapement rates of sublegal lobster would be 

 dramatically improved with the use of the larger vent size. Vented traps tended to be more efficient in 

 releasing sublegal lobster than traps with equivalent lath spacing, supporting the use of synthetic 

 vents. Vent orientation (horizontal versus vertical) did not affect the escapement of sublegal -sized 

 lobster. 



Attempts to adjust the size selectivity of traps to 

 minimize the retention of sublegal-sized lobster 

 have received increasing attention in recent years 

 (Krouse and Thomas 1975; Krouse 1978; Pecci et 

 al. 1978; Nulk 1978; Fair and Estrella^), The in- 

 verse relationship between lath spacing and the 

 sublegal catch has long been recognized (Temple- 

 man 1939; Wilder 1945), while current efforts 

 have been directed toward the development of 

 more precise escapement devices, specifically es- 

 cape vents of various designs. 



A clear reduction in lobster mortality and injury 

 with the use of vented traps has been demon- 

 strated (Pecci et al. 1978); sources of trap related 

 mortality and injury include aggressive interac- 

 tions within the trap and the effects of handling by 

 fishermen. In addition, predation on surface re- 

 leased sublegal lobster may contribute sig- 

 nificantly to mortality (Krouse and Thomas 1975). 



Less information is available on the effects of 



'Rhode Island Department of Environmental Management, 

 Division of Fish and Wildlife, 150 Fowler Street, WickJord, RI 

 02852. 



"Fair, J. J.and B. Estrella. 1976. A study on the effects of 

 sublegal escape vents on the catch in lobster traps in five coastal 

 areas of Massachusetts. Unpubl. manuscr.,9p. Massachusetts 

 Division of Marine Fisheries, P.O. Box 707, Sandwich, MA 

 02563. 



Manuscript accepted Apnl 1979. 



FISHERY BULLETIN. VOL. 77, NO. 4, 1980. 



trap venting on the incidental catch of commer- 

 cially valuable species, particularly the rock crab. 

 Cancer irroratus, and the jonah crab, C borealis. 

 Krouse (1978) demonstrated the effectiveness of 

 vents with circular openings in retaining market- 

 able northern crabs Cancer spp., while permitting 

 the egress of sublegal-sized lobster. Stasko (1975) 

 earlier promoted the use of circular escape open- 

 ings in traps modified to retain crabs and release 

 lobster. 



A research program designed to substantiate 

 data available on trap venting and apprise local 

 fishermen of new concepts in gear modification 

 was initiated by the Rhode Island Division of Fish 

 and Wildlife in April 1976. This report presents 

 the results of field and laboratory investigations 

 on the effects of trap venting on catch per unit 

 effort (CPUE) and size composition of the lobster 

 catch. 



METHODS 



Conventional lobster traps were purchased from 

 commercial suppliers and distributed to eight 

 cooperating fishermen. The fishermen partici- 

 pated on a voluntary basis and were chosen to 

 represent a range of geographical areas within 



925 



