SOMERTON: LIFE HISTORY OF DEEP-SEA KING CRAB 



reflects the degree of reproductive synchrony in 

 the population. If the first interpretation were 

 correct, L. couesi could be as synchronized as P. 

 camtschatica and the heterogeneity in reproduc- 

 tive condition could merely be due to fortuitous 

 timing of the survey. But if the second interpreta- 

 tion were correct, L. couesi would be quite asyn- 

 chronous compared with P. camtschatica because, 

 at least in P. camtschatica, the eyed (developing) 

 eyes would have been spawned at least 4 mo 

 previous to sampling (G. C. Powell ). Although 

 the embryological development of L. couesi eggs 

 was not studied — this would be necessary to 

 completely resolve the question — I believe that 

 the second interpretation, that L. couesi has an 

 asynchronous spawning, is correct because the 

 eggs classified as developing were clearly in a 

 much earlier stage of development than were the 

 hatching eggs. 



The asynchronous spawning of L. couesi is 

 probably related to the great depths which it in- 

 habits. Temperate species having planktotrophic 

 larvae typically have synchronous breeding cycles 

 because of the rather brief periods which are 

 optimum for larval survival. Since seasonal fluc- 

 tuations are damped with depth, L. couesi may be 

 unable to detect seasonal cues with precision, or 

 more likely, may have larvae which do not rise to 

 the euphotic zone and do not need to be synchro- 

 nized with the surface production cycle. Asynchro- 

 nous spawning was also observed for another 

 deepwater crab, Geryon quinquedens (Haefner 

 1978). Crustaceans living at depths greater than 

 L. couesi have such asynchrony in spawning that 

 seasonal peaks in spawning activity are absent 

 (Rokop 1977). 



Size of Maturity 



Maturity of females was determined by the 

 presence of eggs or egg remnants on the pleopods. 

 Thus, reproductive categories 1 and 2 were con- 

 sidered immature and categories 3 to 6 were 

 considered mature. Maturity of males was deter- 

 mined from the size of the chela relative to the size 

 of the carapace using a method discussed in 

 Somerton (1980). This method assumes that when 

 chela and carapace measurements are plotted 

 against each other on a double logarithmic scale. 



the points lie along two straight lines, one describ- 

 ing the relative growth for juveniles, the other 

 describing the relative growth for adults. A com- 

 puter technique was used to iteratively fit two 

 lines to the data until the best fit (minimal 

 residual sum of squares) was achieved (Figure 4). 

 Maturity was then based on the final assignment 

 to one of the two categories. 



50 60 70 80 90100 150 



CARAPACE LENGTH (mm) 



200 



^G. C. Powell, Fishery Biologist, Alaska Department of Fish 

 and Game, Division of Commercial Fisheries, P.O. Box 686, 

 Kodiak, AK 99615, pers. commun. June 1980. 



Figure 4. — Classification of male Lithodes couesi chela height 

 and carapace length measurements into juvenile (dots) and 

 adult (pluses) categories. The relative growth of the chela is 

 described for juveniles by the lower line (CH = 1.52 CL — 4.17; 

 SD for intercept and slope are 0.19 and 0.04) and for adults by the 

 upper line (CH = 1.70 CL - 4.83; SD for intercept and slope are 

 0.13 and 0.03). Regression methods of Somerton (1980), see text. 



The size of 50% maturity was estimated by 

 fitting a logistic equation to the percentage ma- 

 ture by size using the methods discussed in Somer- 

 ton (1980), then evaluating the fitted equation to 

 determine the size corresponding to 50% mature. 

 Percentage mature and the fitted logistic equation 

 are shown for both sexes in Figure 5. Estimated 

 sizes of 50% maturity were 91.4 mm for males and 

 80.2 mm for females. 



Fecundity 



Fecundity of L. couesi increases up to a size of 95 

 mm and remains fairly constant thereafter (Fig- 

 ure 6). The apparent curvilinear relationship 

 between fecundity and size is similar to that 

 reported for P. platypus (Sasakawa 1975) but 

 unlike the strict linear relationships reported for 



263 



