GROWTH OF THE ADULT MALE KING CRAB 



55 



fore the adult form occure at 2 mm., it is unlikely 

 that these 9 mm. crabs are of 0-ajje class, but are 

 ])r()bably 1 year old. 



Furtlier, it is our belief that another year group 

 between 8 mm. and 45 mm. is to be expected. In 

 a study - of the growth of small crabs in Unalaska 

 Bay, Alaska, we sampled at 4-montli intervals 

 from May 1958 through May 1959. By observing 

 the progression of modes in these samples, we con- 

 cluded that crabs sampled in May of 1958 were in 

 their second year at a carapace width of 11 to 12 

 mm. and were in their third year at a carapace 

 width of 37 mm. According to our data, a crab 

 near the end of its third year of life would be ap- 

 proxinaately 45 mm. or larger. If geographic vari- 

 ation in gi'owth is not great, it seems reasonable 

 to expect that if crabs near Japan are about 8 mm. 

 at age 1, then at age 2 they would be less than 37 

 mm., and 45-mm. crabs may be 3 years of age 

 rather than 1-year-old as ix>stulated by Wang. It 

 would then appear that Wang's curve may be 

 shifted 2 years to the right. Also the inclusion of 

 another year group at 115 mm., as noted in Wang's 

 size-frequency distribution, would tend to decrease 

 the slope beyond 85 mm. 



Marukawa (1933), in his comprehensive and 

 informative paper on Paralifhodes, presents a 

 discussion on growth, including the curve shown 

 in figure 1, in which males reach a maximum 

 carapace widtli of 216 mm. in 31 years. A review 

 of Marukawa's methods and results is presented 

 by McKay and Weymouth (1935), who point out 

 that the early modes in Marukawa's size-frequency 

 data probably represent instars rather than year 

 classes, and that later modes most likely indicate 

 chance irregularities. We generally agree with 

 the reviewers. Marukawa's size-frequency distri- 

 butions of smaller crabs show modes at 7, 17, 25, 

 34, 42, and 53 mm., which he interprets as being 

 year classes. As discussed in the previous para- 

 graph, progression of modes in a series of size 

 frequencies taken throughout a year indicates 

 greater spacing between year classes than are 

 shown in Marukawa's size distribution. Sato 

 (1958), also points out that the 17, 34, and 42 mm. 

 modes in Marukawa's frequency curve can be con- 



^iThe results of this study are described briefly In a paper sub- 

 mitted to the International North Pacific Fisheries Commission 

 for inclusion in the 1959 Annual Report. 



sidered as instars. That modes in the larger sizes 

 are due to chance irregularities is su.spected, since 

 our observations of growth increments resulting 

 from one molt would span from 3 to 6 modes. 

 Thus, if some of the early modes were considered 

 instars rather than year classes, the lower portion 

 of Marukawa's curve would be steeper and would 

 shift the remainder of the curve to the left. Con- 

 sideration of fewer age classes in the larger sizes 

 would also steepen the curve, and it would ap- 

 proach maximum size more rapidly. 



Nakazawa (1912) presented information that 

 enabled construction of the curve shown in figure 

 1, but unfortunately he did not include the data 

 upon which his annual growth increments were 

 based. His curve, however, is intermediate be- 

 tween Wang's (1937), whose growth rate appears 

 too rapid, and that of Marukawa's (1933) which 

 appears too slow. Other investigator's results of 

 growth studies have been examined but were not 

 included, since sufficient data were not presented to 

 enable constructing curves. 



The reports examined and the curves presented 

 in figure 1 show wide differences that, as stated 

 earlier, seem to be mainly due to errors in inter- 

 pretation, but may, in part, be due to actual dif- 

 ferences in growth demonstrating the difficulties 

 in estimating growth of king crabs. 



The growth studies to be discussed in the re- 

 mainder of this report pertain to the eastern Ber- 

 ing Sea king crab. Although sexual maturity ap- 

 pears to be attained from 85-95 mm., the term 

 adult used in this report includes all crabs larger 

 than 80 mm. in carapace length. Determination of 

 growth for the smaller sizes is based on modal 

 progressions in size- frequency distributions, since 

 modes are fairly well defined and little is known 

 of growth per molt and molting frequency in these 

 sizes. In the larger sizes, year classes tend to over- 

 lap due to nonmolting crabs, and modes when evi- 

 dent are probably made up of various year classes. 

 For this situation a method was developed which 

 is dependent upon a composite of the amount of 

 growth observed in tagged crabs and the propor- 

 tions observed to molt in any particular year. The 

 resulting growth curve for the larger sizes, there- 

 fore, takes into consideration both molting and 

 nonmolting crabs. 



