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Fishery Bulletin 88(2). 1990 



in both nets divided by the total number of sampling 

 hours in each month. 



To determine the spatial distribution as well as tem- 

 poral changes in abundance offish, lobsters, and crabs, 

 visual underwater censuses of these species were con- 

 ducted during the day using SCUBA across bathy- 

 metric transects. A total of 34 transects were made 

 during June, August, September, and November 1985, 

 and February, April, June, July, September, and Octo- 

 ber 1986. Each transect extended from to ~23 m 

 below MLWL, 5 m wide and ~60-70 m long, covering 

 an area of ~300-350 m^. The transects were surveyed 

 in segments covering each 3-m depth interval. Two 

 divers independently searched each of these areas ex- 

 haustively (in ~20 minutes), recording the number of 

 crabs, lobsters, and fish species (both mobile and ben- 

 thic ones). Two night-dive transects were conducted 

 during September 1985 to determine nocturnal activ- 

 ity patterns of mobile predators. Four additional tran- 

 sects were carried out in May 1985 to estimate sub- 

 strate heterogeneity along the depth gradient. Each 

 transect consisted of a polypropylene line extended 

 over the rocky bottom from to 23 m below MLWL. 



In each of these transects, at depth intervals of 3 m, 

 we recorded the number of crevices, holes, and bur- 

 rows (shelters) larger than 5 cm in aperture occurring 

 to a distance of half a meter to the right and to the 

 left of the line. 



One-way ANOVA followed by a Student-Newman - 

 Keuls (hereafter SNK) multiple comparison test (Sokal 

 and Rohlf 1969) were employed for the detection of 

 changes in abundance of predators and shelters (sub- 

 strate heterogeneity) over the temporal and bathy- 

 metric gradients studied. 



Results 



Species composition 



A total of 4 species of decapod crustaceans, including 

 1 lobster species {Homarus americanus) and three spe- 

 cies of crabs (Cancer irroratus, C. borealis, and Carci- 

 nus maenas), and 23 species of fish (624 specimens) 

 were captured or observed from June 1985 to October 

 1986 (Table 1). 



