KROUSE: DISTRIBUTION OF JONAH AND ROCK CRABS 



Table 2. — Monthly captures and sex ratios of Jonah crabs 

 caught with research traps. 1968-74. Asterisks denote sig- 

 nificant deviation from 1:1 Ichi-square). 



Upper Sheepscot River 



 ■486'' 



NS = not significant 

 • = PcO.05 

 •• = P- 01 



European edible crab have been reported to move 

 inshore in spring and offshore in fall (Dewberry 

 1956; Hoopes 1973; Brown see footnote 3). In fact, 

 mature female European edible crabs have been 

 observed to move considerable distances ( ^225 

 km) along the coast of England (Brown see foot- 

 note 3). 



Sex ratios of rock crabs caught with research 

 gear varied not only by season but also by area 

 (Figui-e 7). From July through September females 

 generally outnumbered males, throughout the fall 

 many of the sex ratios approximated a 1;1 relation, 

 and then in winter males were dominant except in 

 the upper Sheepscot River where they predomi- 

 nated only in May. Similar to Jonah crabs, sea- 

 sonal variations in rock crab sex ratios may best be 

 explained by changes in the crabs' availability and 

 vulnerability to the research traps in association 

 with shedding and mating behavior. For instance, 

 peak catches of females during summer and early 

 fall coincided with egg hatching (summer) and 

 molting (fall) in Maine waters (Krouse 1972). 



Higher proportions of male rock crabs in winter 

 and spring catches may be attributed to: 11 re- 

 cruitment of males as the result of winter-spring 

 shedding (Krouse 1972) and, possibly, inshore 

 movement (Haefner [1976] suggested that male 

 rock crabs in the Mid-Atlantic Bight undertake 

 seasonal inshore-offshore migrations); 2) in- 

 creased feeding activity of newly molted crabs; 

 and 3) a reduction in the availability and vulnera- 

 bility of females during the winter spawning 

 period (Dewberry [19561 noted that ovigerous 

 female C. pagurus consume little food). Through- 

 out summer the number of male rock crabs, par- 

 ticularly those 90 mm CW, diminished due to 

 fishing mortality and, perhaps, an offshore move- 

 ment. 



The upper Sheepscot River sites, unlike the 

 other locations, had a preponderance of female.^ 

 during fall and winter, yet in spring, similar to 

 other areas, males were more numerous (Figurt 

 7). Perhaps this relatively high abundance of 



Jan Feb Mar Apr May June July Aug Se'pl Oct Nov Dec 

 MONTHS 



Figure 7. — Monthly percent frequencies of female rock crabs 

 caught by research traps at different locations in the Boothbay 

 region. 1968-74. Numbers in parentheses represent total 

 number of males and females. Those ratios differing sig- 

 nificantly from 1:1 (P = 0.05 by chi-square) are marked with 

 asterisks. Blank bars represent no fishing effort. 



females may be related to the Sheepscot River 

 sites' soft mud substrate, which females apparent- 

 ly seek during the spawning season. From 

 laboratory observations it appears that unless 

 females are burrowed in the substrate at the time 

 of egg extrusion, many eggs will not become at- 

 tached to the pleopods resulting in a significantly 

 reduced complement of eggs. Edwards and Early 

 ( 1972) reported that female C. pagurus also show 

 preference for soft substrates during the spring. 

 Lindsay (1973) also noted that sex ratios ol 

 Maine rock crabs vary by locality and sea.son. He 

 also found males to be more abundant in the 

 winter and spring. 



\\ id th- Weight Relations 



Because the overlap of data of males and 

 females composed only a small segment of the 

 total range of sizes, I applied analysis of 

 covariance to the total regressions as well as the 

 partial regressions derived from the data that 



691 



