EFFECTS OF BEHAVIORAL INTERACTIONS ON THE CATCHABILITY 



OF AMERICAN LOBSTER, HOMARUS AMERICANUS, 



AND TWO SPECIES OF CANCER CRAB 



R. Anne Richards, 1 J. Stanley Cobb, 1 and Michael J. Fogarty 2 



ABSTRACT 



Intraspecific and interspecific behavioral interactions may affect the probability of capturing 

 Cancer irroratus, C. borealis, and Homarus americanus in lobster traps. To test this hypothesis, the 

 catch per unitof effort(CPUE)of eachof these species in trapsstocked with C. irroratus, C. borealis, 

 or H. americanus was compared with that obtained from empty baited traps (controls). 



In traps stocked with lobsters, the catch of all three species was significantly reduced. Traps 

 stocked with 8 lobsters caught significantly fewer crabs than traps containing 3 lobsters. The only 

 effect of stocking traps with crabs was to increase the catch of C. borealis in traps stocked with 3 

 crabs of either species. Results of laboratory experiments comparing crab CPUE in control traps 

 with crab CPUE in traps stocked with 8 lobsters concurred with the field results. 



When H. americanus was stocked in the holding section (parlor) of the trap, a greater proportion 

 of the crab catch was found in the entrance section (kitchen ). This behavioral response may facilitate 

 escape of crabs from traps containing H. americanus. The distribution of the lobster catch was un- 

 affected by stocking H. americanus or Cancer crabs in the parlor. 



Behavioral mechanisms underlying reductions in crab CPUE were investigated by laboratory 

 observation of an actively fishing trap. When H. americanus was stocked, C. borealis avoided 

 entering traps. Cancer irroratus entered the kitchen of traps containing H. americanus, but the 

 proportion entering the parlor was reduced. The escape rate of both crab species increased in traps 

 stocked with H. americanus. The position underneath the entrance to the parlor was preferred by 

 all species. When both H. americanus and Cancer crabs were present in the trap, H. americanus 

 occupied that position. 



A number of environmental and biological fac- 

 tors are known to affect the probability of cap- 

 turing crustaceans in traps. Water temperature 

 and salinity are positively correlated with cap- 

 ture rates of rock lobster, Panulirus cygnus, 

 (Morgan 1974), and a linear relationship between 

 temperature and the catchability of American 

 lobster, Homarus americanus, was found by 

 McLeese and Wilder (1958). Biological rhythms 

 and physiological changes, such as those asso- 

 ciated with the molt cycle (e.g., Chittleborough 

 1975), may affect feeding and other activities 

 (e.g., Bennett 1974; Morgan 1974) and thus cause 

 fluctuations in catchability. In addition, behav- 

 ioral attributes such as avoidance of dead con- 

 specifics (Hancock 1974; Morgan 1974; Chapman 

 and Smith 1979), intraspecific attraction (re- 

 viewed in Hancock 1974), or competitive relations 



'Department of Zoology, University of Rhode Island, King- 

 ston, RI 02881. 



2 Rhode Island Department of Environmental Management, 

 Division of Fish and Wildlife. 150 Fowler St., Wickford, RI 

 02852; present address: Northeast Fisheries Center Woods 

 Hole Laboratory, National Marine Fisheries Service, NOAA, 

 Woods Hole, MA 02543. </-Lft 



(Bennett 1974; Ricker 1975; Caddy 3 ) may affect 

 catch rates. The potential importance of such in- 

 teractions between animals converging on a trap 

 has been recognized by several authors (Bennett 

 1974; Bennett and Brown 4 ; Caddy footnote 3; 

 Miller 1978, 1979a, b, 1980; Fogarty and Borden 

 1980). 



The present study was designed to determine 

 whether trap efficiency, the number of individ- 

 uals captured as a fraction of those detecting the 

 gear (Caddy footnote 3), for Jonah crab, C. bo- 

 realis, rock crab, C. irroratus, and H. ameri- 

 canus is affected by the presence of others of 

 these species in the traps. Additional null hypoth- 

 eses were that 1) trap efficiency is independent of 

 the density of other species in the trap, and 2) the 



Manuscript accepted June 1982. 



FISHERY BULLETIN: VOL. 81. NO. 1, 1983. 



Caddy, J. F. 1977. Some considerations underlying defi- 

 nitions of catchability and fishing effort in shellfish fisheries, 

 and their relevance for stock assessment purposes. ICES 

 Shellfish and Benthos Committee Ref. Gear and Behavior 

 Committee, No. 18, 22 p. 



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

 pot immersion time in recording and analyzing catch-effort 

 data from a trap fishery. ICES Special Meeting on Popula- 

 tion Assessments of Shellfish Stock, No. 6, 9 p. 



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