KROUSE DlSTRrBUTION OF JONAH AND ROCK CRABS 



Additional commercial catch data were pro- 

 vided by Joel Cowger, Maine Department of" 

 Marine Resources, West Boothbay Harbor, Maine, 

 who obtained measurements of 299 commercially 

 caught Jonah crabs from the Maine coast (Sep- 

 tember 1977-March 1978). Carapace widths were 

 measured between the tips of the outermost an- 

 terolateral spines. These long carapace width 

 measurements can be converted to short carapace 

 width (distance between notches) by the linear 

 regression Y = -1.669 + 0.973X where Y = short 

 CW and A' = long CW (Carpenter 1978). 



RESULTS AND DISCUSSION 



Size Ciiinposituin 



Jonah crabs captured with research traps 

 (mean 104.8 mm CW for females and 113.7 mm 

 for males) were significantly smaller (^-test, 

 P<0.01) than those crabs commercially landed at 

 either Boothbay Harbor (mean 114.0 mm CW for 

 females and 128.6 mm for males) or at other 

 Maine ports (mean 114.0 mm CW for females and 

 141.1 mm for males) (Figures 3-5). At first it was 

 thought that disparities in size composition 

 might be associated to variations in selectivity of 

 the research and commercial gear for crabs <95 



mm CW; however, since similar proportions of 

 small crabs appeared in both the research and 

 commercial catches (Figures 3-5), the effects of 

 gear selectivity must be minimal. The near total 

 absence of crabs -95 mm CW in the commercial 

 catch from Boothbay Harbor (Figure 4) was the 

 result of fishermen discarding the smaller crabs 

 before their landed catches were measured; 

 whereas, the catches shown in Figures 3 and 5, 

 which were measured at sea, included all crabs 

 caught. Thus, I attribute these size disparities to 

 spatial variations in the distribution of different 

 size crabs. For instance, research traps were 

 fished at depths of 3-20 m, whereas, most com- 

 mercial traps were fished at depths of 12-91 m. In 

 support of this contention, different size groups of 

 Jonah crabs have been observed to be distributed 

 within the Mid-Atlantic Bight according to depth 

 (Haefner 1977; Carpenter 1978). 



Male Jonah crabs averaged larger than females 

 in all catches (Figures 3-5); similarly, male rock 

 crabs generally averaged larger than females 

 (Krouse 1972). Unlike female rock crabs, which 

 have no commercial value because of their small 

 size (rarely >100 mm CW, Krouse 1972), female 

 Jonah crabs, which approximate the size of male 

 rock crabs, are commercially harvested along 

 with male Jonah crabs. 



6r 



60 



80 



100 110 



CARAPACE WIDTH (mm) 



20 



140 



FIGURE 3.— Width-frequency distributions of male and female Jonah crabs caught with research traps in the Boothbay Harbor 



region, 1968-74, 



687 



