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Figure 67.— Distribution and abundance of Cancer irrorulus in the New York 

 Bight apex. 



FEEDING ECOLOGY: This species is known to be a scavenger 

 and carnivore. MacKenzie ( 1977) reported that it preys upon small 

 clams, while Scarratt and Lowe (1972) have observed that prey of 

 rock crabs >25 mm in size consisted principally of polychaetes. 

 mussels, starfish, and sea urchins. 



Rock crab juveniles and adults are preyed upon by several spe- 

 cies of fish including cod. Gadus moriuta: little skates. Raja erina- 

 cea: red hake. Urophycis chuss; striped bass. Morone saxatilis: 

 tautog. Tautoga onitis; and haddock. Melanogrammus aeglefinus 

 (Field 1907; Bigelow and Schroeder 1953: Wigley 1956: Wigley 

 and Theroux 1965: Reilly 1975; Reilly and Saila 1978). 



Ennis (1973) reported that in Bonavista Bay. Newfoundland. C. 

 irroratus and other decapods make up almost 50% of the gut con- 

 tents of the lobster Homarus americanus. 



REPRODUCTION AND GROWTH: In the Northumberland 

 Strait. Gulf of St. Lawrence. Scarratt and Lowe (1972) found the 

 smallest size at maturity was 60 mm for females and 69 mm for 

 males, with breeding occurring in late summer and fall. Larvae are 

 present in surface waters from June to September. In the Gulf of 

 Maine. Krouse ( 1976) observed that most females attained sexual 

 maturity between 70 and 80 mm carapace width, with a few at < 70 

 mm. Spawning is believed to occur in late fall and early winter and 

 hatching occurs in spring. In southern New England waters. Reilly 

 and Saila (1978) reported that females in the 21-88 mm carapace 

 width range could produce between 4.430 and 330.400 eggs 

 individual. The presence of ovigerous females <50 mm in size 

 indicated earl) sexual maturity. Spawning occurred in the spring 

 with major hatching in May. July was the principal period for larval 



settlement. In Narragansett Bay, Sastry and McCarthy (1973) 

 found ovigerous females with eggs nearing hatching from late April 

 to early June. Hillman (1964) first found C. irroratus larvae in Nar- 

 ragansett Bay in late May. while Frolander (1955) found larvae 

 from April to late October in the same waters. Coastal New Jersey 

 plankton surveys by Sage and Herman (1972) revealed C. irroratus 

 larvae in late spring samples. In a Chesapeake Bay study. Sandifer 

 (1975) observed that ovigerous females are infrequent in the bay 

 and most larvae appear to hatch offshore. Although larvae are toler- 

 ant of moderate estuarine salinities, zoeae probably are retained 

 within the Bay only by chance. Bay or nearshore populations are 

 apparently restocked by migration or transport by currents of late 

 larval stages and juveniles from the inner shelf area. The optimum 

 growth rate of C. irroratus larvae occurs at 15°C and 30%„ (Sastry 

 and McCarthy 1973). 



Uneven sex ratios for this species are not unusual. Large male: 

 female ratios have been observed in Maine (Dean 1972), 16 the 

 Northumberland Strait (Scarratt and Lowe 1972). and in Virginia, 

 where there is an absence of females in winter populations (Shotten 

 and Van Engel 1971), 1? possibly the result of population move- 

 ments restricted to one sex (Jones 1973). 



Cancer irroratus lives for 7 to 8 yr (Reilly and Saila 1978). In the 

 Middle Atlantic Bight, active molting takes place in April and June 

 (Haefner 1976) and growth ceases in winter. 



ADDITIONAL INFORMATION: Vargo and Sastry (1977) con- 

 ducted an experiment to determine the tolerance limits to acute 

 temperature and combinations of temperature and low dissolved 

 oxygen stresses for five zoeal stages and the megalops of C. irrora- 

 tus. Results showed that the acute temperature limits for a 120-min 

 exposure were all approximately 29.0°C. with little interstage vari- 

 ation, while those for 240 min ranged from 27.3° to28.5°C. Most 

 interstage variation was shown when temperature and low dis- 

 solved oxygen were combined, with low oxygen tolerance decreas- 

 ing as temperature increased. The megalops is relatively insensitive 

 to changes in oxygen concentration with temperature. It was con- 

 cluded that larval stages have the capacity to tolerate a wider range 

 of these variables than they experience in the natural environment. 



In another study, Bigford (1977) cultured larvae of C. irroratus 

 and exposed them to 0.0, 0.1. and 1.0 ppm concentrations of a 

 water-accommodated fraction of No. 2 fuel oil under static condi- 

 tions. Behavioral changes were monitored in terms of watercolumn 

 reponses to various conditions of light, pressure, and gravity. The 

 most important effects of these sublethal exposures were the rever- 

 sals of normal larval gravity responses in the watercolumn. Results 

 were that the normally geonegative, early stage larvae moved 

 lower in the water column and the normally benthic megalops stage 

 rose in the watercolumn. This depression of typical megalopal ben- 

 thic behavior in exposed larvae could alter recruitment to adult pop- 

 ulations. As noted previously, Sandifer (1975) stated that C. 

 irroratus apparently do not return to their adult habitats during 

 planktonic stages. Instead, late larval stages and juvenile crabs join 

 adult populations via extensive migrations. Therefore, alteration of 

 late larval stage benthic behavior patterns could keep most larvae 

 out of bottom shoreward currents that aid in recruitment move- 

 ments. It was also determined that the 1 .0 ppm concentration of this 

 fuel oil is very near the lethal dose for these larvae. 



'"Dean. D. (editor). 1972. The University of Maine's Sea Grant Program for 1 

 May 1971 to 30 April 1972. Univ. Maine. Orono, 25 p. 



l7 Shotten. L... and W. Van Engel. 1971 . Distribution, abundance and ecology of 

 the rock crab {Cancer irroratus) in Virginia coastal waters of the Chesapeake Bight 

 of the Virginia Sea. Va. Inst. Mar. Sci. Rep. 40, 3 p. 



46 



