SOMERTON: LIFE HISTUKY OF DEEP-SEA KING CKAH 



apparently close to hatching, and had been stored 

 in SS*"/ isopropyl alcohol after being fixed in 

 Formalin. 



RESULTS AND DISCUSSION 



Depth Distribution 



Specimens of L. couesi were collected in every 

 trap set from the shallowest in 384 m to the 

 deepest in 850 m. Four sets on two seamounts were 

 at depths less than the depth range (542-1,125 m) 

 previously recorded for this species (Sakai 1971). 



Lithodes couesi occurs shallower on seamounts 

 than on the continental slope. This hypothesis is 

 supported by the results of a concurrent NMFS 

 survey of the southeast Alaska continental slope 

 that sampled roughly the same latitudes (54°-58° 

 N) and depths ( 237-711 m) and used the same types 

 of traps as the seamount study. Although depths 

 <550 m were thoroughly sampled, specimens of 

 L. couesi were not taken in <592 m (H. Zenger ). 



The shallow distribution of L. couesi on sea- 

 mounts may be due to the absence of a predator or 

 competitor which is able to exclude it from similar 

 depths along the continental slope. Because sea- 

 mounts are isolated from the ocean surface and 

 from coastal areas, they are essentially submarine 

 islands inhabited only by species that are able 

 to tolerate the available depth range and that 

 possess sufficient dispersal capabilities to reach 

 seamounts from the continental slope. If a pred- 

 ator or competitor were unable to colonize the 

 seamounts, L. couesi may respond by expanding 

 its range into shallower water. A similar pattern 

 of competitive release and altitudinal expansion 

 has been reported for birds on South Pacific 

 islands (Diamond 1975). 



Size Distribution 



The size distribution of each sex was nearly 

 unimodal with a mode at about 108 mm for males 

 and 92 mm for females (Figure 2). The lack of an 

 appreciable number of crabs <70 mm is probably 

 due to size selectivity of the sampling gear, rather 

 than a lack of small crabs on the seamount tops, 

 because three of the four smallest specimens were 

 caught with a bottom trawl in an area of the 



CO 



m 

 < 



DC 

 O 



LU 



m 



50 



40 



30 



20 



10 



""H. Zenger, Fishery Biologist. Northwest and Alaska Fish- 

 eries Center, National Marine Fisheries Sei-v'ice. NOAA, 2725 

 Montlake Boulevard East, Seattle, \VA 98112, pers. commun. 

 June 1980. 



60 80 100 120 



CARAPACE LENGTH (mm) 



Figure 2. — Size distribution of male (solid linei and female 

 I dotted line) Lithodes coueni by 2 mm .size intervals from trap 

 samples from Gulf of Alaska seamounts. 



Patton Seamount where only larger crabs were 

 obtained with traps. 



Other species of king crabs, especially P. cam- 

 tschatica and P. platypus, display size stratifica- 

 tion with depth; adults generally occur deeper 

 than juveniles (pers. obs.). To determine if L. 

 couesi also stratify, crab size was regressed 

 against depth. Only the sizes of crabs from sable- 

 fish traps were used in the regression because 

 king crab traps caught significantly larger crabs 

 than sablefish traps when both types were fished 

 together ( ^-test, P < 0.001) and because king crab 

 traps were not used on every seamount. For males, 

 the slope of the regression line was not significant 

 (P = 0.289). For females, the slope was signifi- 

 cant (P = 0.030) and negative, indicating that 

 larger females occur in shallow water. However, 

 there was little variation in sampling depth on 

 each seamount; thus, size variation with depth 

 cannot be separated from size variation between 

 seamounts. 



Sex Ratio 



In total, 880 females and 577 males were cap- 

 tured in 24 trap sets. The large preponderance of 

 females suggested that the sex ratio may not be 

 1:1. If the sex of each specimen were independent of 

 the sex of other specimens in the same set, then 

 the observed proportion male, 0.40, is signifi- 



261 



