Stehlik et al.: Distribution patterns of various crab species in the Hudson-Rantan Estuary 



697 



25 and 30 ppt. Salinity decreased with distance from 

 the bay mouth and in any one month, the difference 

 in salinity between stations at the estuary mouth and 

 those at the westernmost part of the study area was 

 approximately 5-10 ppt. 



Catch by species, size, and sex 



From June 1991 through December 1994, more than 

 68,000 blue, lady, and rock crabs were caught in 1200 

 otter trawl tows (Table 1). Other mega-invertebrates 

 in the tows included the northern moonsnail (Euspira 

 heros), the horseshoe crab (Limulus polyphenols), the 

 American lobster (Homarus americanus), the portly 

 spider crab (Libinia emarginata), the flatclaw hermit 

 crab tPagurus pollicaris), mud crabs (Xanthidae), and 

 the sea star (Asterias sp. ) 



Catch per tow of crabs by size class increased as 

 they became large enough to be retained by the mesh 

 of the net (Fig. 2). Abundances of female blue and lady 

 crabs in the study area were greater than those of the 

 males. In rock crabs, males predominated (Table 1). Im- 

 mature blue and lady crabs had sex ratios fairly close 

 to 1:1 (male:female). Sex ratio in mature blue crabs, 

 however, was 1:1.97, and in mature lady crabs, 1:2.12. 

 In all sizes of rock crabs, sex ratio strongly favored 

 males, particularly in mature crabs, in which the ratio 

 was 21.43:1. 



Temporal and spatial variation in catch 



The maximum relative abundance of blue and lady 

 crabs occurred during the warm months each year, 

 whereas rock crabs were abundant only in the cold 

 months (Fig. 3). Blue crabs were scarce in the otter 

 trawls from January through May or June. We believe 

 that many of them do remain in the study area, but are 

 relatively inactive and are not accessible to otter trawls, 

 as discussed below. Lady crabs migrated into the estu- 

 ary in April and May and left in October and November. 



15 



10 



5 







a" 



^ 20 



o 



c 

 a> 



cr 

 a> 



r 10- 



Blue crabs 



r*r¥P 



ml 



I 



-^r 



I 



Lady crabs 



Male 

 I Female 



IL 



4 8 12 16 20 



Carapace width (cmL 



Figure 2 



Carapace width (cm) frequencies for male and 

 female blue, lady, and rock crabs collected 

 during the Hudson-Raritan Estuary trawl 

 survey, June 1991-December 1994, by percent 

 frequency of the total catch of each species. 



