Cancridae 239 



Family cancridae 



NOTES ON REARING THE PACIFIC EDIBLE CRAB, 

 CANCER MAGISTER 



Donald C. G. MacKay, Pacific Biological Station 



THE Pacific edible crab, Cancer magister, described by Dana in 1852, 

 is a large crustacean which sometimes reaches a carapace width of 22 

 cm. In Alaska, British Columbia, Washington, Oregon, and California 

 the species is present in large numbers. 



LIFE HISTORY 



Evidence from several independent sources leads to the conclusion that 

 females become mature at a carapace width of approximately 10 cm. 

 The size at which sexual maturity is attained in males has not been 

 ascertained definitely but it is known that some are mature at a width of 

 13.5 cm. Maturity is ordinarily attained by females in the 4th or 5th 

 year though, in some instances, it is believed to occur as early as the 

 3rd year or as late as the 6th year. The normal duration of life in 

 British Columbia is probably about 8 years and the maximum is prob- 

 ably not more than 10 years. 



The mating season is from April until September. Mating takes place 

 on the tide flats and invariably occurs between a soft-shelled female and 

 a hard-shelled male. The male embraces the female, sternum to sternum, 

 and the two lie buried in the sand, mud, or seaweed in a nearly vertical 

 position. 



The average diameter of fully developed external eggs is about 0.47 

 mm. During development the ovarian eggs undergo color changes from 

 white to coral red; these changes are closely correlated with the sizes of 

 the eggs. The number of eggs produced by Cancer magister is large, the 

 actual number depending upon the body size. In two specimens exam- 

 ined the numbers were 750,000 and 1,500,000 for crabs 5.33 and 6.00 

 cm. in carapace width respectively. It is estimated that one female in a 

 lifetime might produce 4,000,000 eggs. 



The ovigerous period in British Columbia is from October until June. 

 Hatching probably occurs from December until June and there is reason 

 to believe that the season is somewhat earlier in California. 



The eggs hatch as protozoeae and pass through several zoeal instars 

 and one megalops instar, after which they closely resemble the adult in 

 form. 



The natural sizes of the megalops and first five post-larval instars have 

 been determined and are respectively as follows: 0.28, 0.52, 0.74, 0.97, 

 1.34, and 1.82 mm. Contrasted with the natural increases just men- 



