OBSERVATIONS OF MOLTING FEMALE KING CRABS 



(Paralithodcs camtschatiea) 



INTRODUCTION 



The Pacific Salmon Investigations of 

 the U. S. Fish and Wildlife Service is 

 conducting studies to determine the need 

 for measures for conservation of the 

 eastern Bering Sea king crab ( Paralithodes 

 camtschatiea ), as part of the research pro- 

 gram of the International North Pacific 

 Fisheries Commission. In this respect, 

 knowledge of the biology of the king crab 

 is essential. 



Molting, an important phase in the 

 life history of king crab as well as other 

 crustacea, is a phenomenon whereby the 

 exoskeleton is periodically discarded. 

 Generally all the outer cuticular layers 

 of the shell, eyes, antennae, gills, 

 tendons, mouth parts, esophagus, and 

 stomach with its chitinous teeth are re- 

 placed, leaving no apparent trace of this 

 change. The age of the crab, therefore, is 

 extremely difficult to determine. One of 

 the methods of estimating age is to rear 

 crabs in order to observe the molting 

 frequency and measure the growth attained 

 from molting. These measurements combined 

 with those obtained by sampling the fishery 

 then may give some indications of age . 



ThiB report describes the observations 

 of nine molting female king crabs caught in 

 Pavlof Bay on the Alaska Peninsula between 

 May 1 and 18, 1957 • Work was done aboard 

 the MV Deep Sea , a king erab factoryship. 



I am grateful to Wakefield's Deep 

 Sea Trawlers Inc. and the crew of the 

 vessel for their cooperation and the use 

 of their facilities. My thanks also to 

 Mr. Glen Davenport for his assistance, and 

 Mr. T. 0. Duncan for photographs. 



PREMOLTING OBSERVATIONS 



The fuinnal molting and mating period 

 of female king crabs occur in the spring. 

 At this time the male is observed holding 

 the meropodite of the chelipeds of the 

 female with his chela. After the female 

 molts, the male leaves the cast shell and 

 resumes the original "hand shaking" position 

 with the soft-shelled female. The female 



then lays new eggs which attach to the 

 swimmerets in the abdominal pouch and are 

 fertilized. Shell -casting, however, can 

 take place without the male. 



Upon capture, the crabs were placed 

 in live boxes provided with running sea 

 water. For identification each crab was 

 marked with a number on the carapace be- 

 fore and after molting. Carapace length 

 measurements and examinations were made 

 daily from the time of capture until re- 

 lease. 



The nine female specimens in a pre- 

 molting condition had similar external 

 characteristics. The shells of the cara- 

 pace and appendages were thin and pliable. 

 The membranes connecting the shell parts 

 were also very thin and cellophane -like in 

 texture. A slight pink color, differing 

 from the opaque color found in crabs of 

 nonmolting condition, was detected under 

 the thin membranes at the joints of each 

 leg and between the plates of the abdomen. 

 On one specimen the suture along the 

 anterior border of the first abdominal 

 segment was split and the pink soft shell 

 exposed. (See figure 1 for arrangement of 

 the abdominal segments. ) The eyes of the 

 specimens were bright red in contrast to 

 the brown colored eyes of nonmolting crabs. 



Prior to molting, the female crabs 

 were observed with their bodies lifted off 

 the bottom of the live box. Their abdomens, 

 extended away from their bodies, moved 

 rhythmically back and forth exposing the 

 swimmerets covered with empty egg cases. 

 This behavior was seen frequently until 

 molting and may be beneficial in releasing 

 zoea larvae as well as loosening the soft 

 shell from the old, making extraction 

 easier during the shell-casting process. 



MOLTING OBSERVATIONS 



The first step observed in the shell - 

 casting process was a separation in the 

 thin membrane anterior to the first abdomi- 

 nal segment. (See figure 1 for arrange- 

 ment of the membrane connecting the 



