Somerton and Donaldson Biology of Chionoecetes tanneri and C. angulatus 



353 



C. tanneri males 



C angulatus males 



40 60 100 160 



40 60 100 160 



Figure 5 



Size at 509c maturity I W XI ) for male Chionoecetes tanneri and C. angulatus. 

 Upper graphs show the assignment of chela height and carapace width 

 data to juvenile (dot) and adult (plus) categories. The number of observa- 

 tions in each category (n a for adults, n for juveniles) is indicated in the 

 appropriate graph. Lower graphs show the fit of a logistic model (solid 

 line) to the proportion mature within 1-mm size categories. Dotted lines 

 show the carapace width associated with a 0.50 proportion mature. 



Synchronous seasonal reproduction is not necessar- 

 ily the norm for slope-dwelling crabs. For example, the 

 two species of king crabs that also inhabit the eastern 

 Bering sea slope, Lithodes aequispina and L. couesi, 

 have asynchronous and nonseasonal reproduction 

 (Somerton, 1981b; Somerton and Otto, 1986) as evi- 

 denced by a wide variation among adult females in the 

 developmental stages of their embryos. These king crab 

 species also have eggs that are more than twice the 

 diameter of eggs from shallow-water king crabs, such 

 as Paralithodes camtschaticus, and have exceptionally 

 large larvae provisioned with a greater amount of yolk 

 (Somerton, 1981b). Such larvae may be lecithotrophic 

 (i.e. nonfeeding) and therefore remain at depth through- 

 out their development. This larval strategy could, in 

 turn, reduce or eliminate larval dependency on the sea- 

 sonal production of food and thus obviate the need for 

 seasonal reproduction (Somerton, 1981b). For C. tannen 

 and C. angulatus, however, the mean egg diameter is 

 only slightly larger than that for the shallow-water 

 species C. bairdi and C. opilio, indicating that C. tanneri 



C. tanneri females 



40 60 80 100 



C. angulatus females 



o 



CL 



4U 



60 



80 



100 



Carapace width (mm) 



Figure 6 



Size at 507c maturity (W 50 ) for female 

 Chionoecetes tannen and C. angulatus. For 

 each species is shown the fit of a logistic 

 model ( solid line ) to the proportion mature 

 within 1-mm size categories. Dotted lines 

 show the carapace width associated with 

 a 0.50 proportion mature. Number of 

 adults and juveniles sampled are indicated 

 in each graph. 



and C. angulatus probably have planktotrophic larvae 

 which must migrate to feed in surface waters where 

 prey concentrations are greater. Although such onto- 

 genetic vertical migrations by the larvae of deep-sea 

 fauna were once considered improbable, it is now known 

 that a variety of taxa, from depths even greater than 

 those for C. tanneri or C. angulatus, possess vertically 

 migratory planktotrophic larvae (Young, 1994). 



Molting 



For mature female C. tanneri and C. angulatus, rela- 

 tive abundance of the four shell-condition categories 



