FISHERY BULLETIN; VOL. 74, NO. 4 



When growth resumed in late spring and sum- 

 mer, only a few juveniles (previous year's young- 

 of-the-year) were <10 mm CW (stage VI). Unfor- 

 tunately, the overlapping of modes prevented any 

 objective determination of the upper limit of this 

 second modal grouping that represented the 

 juvenile crabs. Nevertheless, several of the 

 monthly distributions (September-October 1972 

 and August 1973) exhibited an upper limit around 

 40 mm CW for this second modal grouping (Figure 

 2). 



Although it was not possible to make precise 

 determinations of age and growth from informa- 

 tion of this study, the data suggest that young- 

 of-the-year crabs ranged in size from about 4 to 20 

 mm CW (instars III-IX) and the juveniles in their 

 second fall ranged from approximately 15 to 40 

 mm CW (instars VIII-XII). 



Hand -Collected Vs. 

 Trap-Caught Crabs 



Prior to sampling small crabs in the intertidal 

 zone, our rock crab work was based on incidental 

 catches of crabs with wire lobster traps (25.4- 

 x25.4-mm mesh) in the Boothbay Harbor area 

 (Krouse 1972). Histograms plotted by 1-mm in- 

 crements for 2,426 hand-collected and 5,480 trap- 

 caught crabs (1972-74) graphically revealed 

 marked differences in size composition of the 

 catches for these two methods of capture (Figure 

 3). Average width for hand-collected crabs was 

 23.9 mm and 78.8 mm for trapped crabs. Even 

 though these two complementary modes of cap- 

 ture sampled a broad range of sizes (2-133 mm 

 CW), many crabs between 40 and 60 mm CW 

 eluded either type of collection. This scarcity of 

 crabs between 40 and 60 mm CW can be attributed 

 to: 1) selectivity of traps against sizes <60 mm CW 

 (based on Figure 3, crabs <70 mm CW were not 

 fully vulnerable to the gear), and 2) movement of 

 crabs >40 mm CW from the intertidal zone in 

 association with low winter temperatures and 

 possible behavioral changes with size. Scarratt and 

 Lowe (1972) reported that small rock crabs (<65 

 mm CW) in the Northumberland Strait, Gulf of St. 

 Lawrence, inhabited rocky areas, whereas larger 

 crabs left the rocky substrate for sand and mud 



bottoms. Jeffries (1966) noted that C. irroratus 

 dwelled chiefly on sand in the Narragansett 

 Bay- the type of bottom this species is adapted to 

 because of its well developed walking and bur- 

 rowing abilities. 



ACKNOWLEDGMENTS 



I thank A. Dolloff, C. Crosby, and D. Libby for 

 their assistance with field collections and data 

 compilations. I am also grateful to J. C. Thomas 

 for his review of this paper. 



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