FISHERY BULLETIN: VOL. 81. NO. 1 



location of animals within the trap is unaffected 

 by the presence of other species. Laboratory ob- 

 servations of the behavior of the two crab species 

 in and around traps were made to assess pro- 

 cesses influencing their catch rates and to inves- 

 tigate the allocation of space in the trap by cap- 

 tured animals. 



METHODS 



Trap Efficiency 



Field studies were carried out from 27 July to 

 30 August 1979 to investigate the effects of intra- 

 specific and interspecific interactions on the 

 catch perunitof effort (CPUE) of C. irroratus, C. 

 borealis, and H. americanus. The catch obtained 

 in lobster traps stocked with these three species 

 was compared with the catch obtained in un- 

 stocked traps. It was assumed that equal num- 

 bers of animals were attracted to all traps; thus 



any differences in CPUE would be due to differ- 

 ences in trap efficiency caused by animals stock- 

 ed in the traps. 



The 18 lobster traps were 91 X 25 X 46 cm, con- 

 structed from galvanized aluminum mesh (2.54 

 cm 2 openings) with no escape gaps (Fig. 1). Traps 

 were set three to a string, with three strings at 

 each of two locations in Narragansett Bay, R.I. 

 One location was an area of coarse sand overlain 

 with boulders, a substratum where C. borealis 

 and H. americanus are typically found. The other 

 location was a predominantly sand bottom where 

 C. irroratus and H. americanus occur (Jeffries 

 1966; Fogarty 1976). Traps within strings were 

 about 13 m apart, strings in each location were 15 

 to 60 m apart, and the locations were separated 

 by about 1 km. Water depth varied from 8 to 14 m. 



In each string of three traps, the middle trap 

 was stocked with 8 individuals of a given species, 

 one end trap contained 3 individuals of that spe- 

 cies, and the other end trap was not stocked and 



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Figure 1.— Lobster trap used in field experiments. 



52 



