CONTRIBUTION TO THE LIFE HISTORY OF THE DEEP-SEA KING CRAB, 

 LITHODES COUESI, IN THE GULF OF ALASKA^ 



David A. Somerton 



ABSTRACT 



Lithodes couesi is a deepwater relative of the commercially important Alaskan king crabs, 

 Paralithodes camtschatica, P. platypus, and L. aequispina. Compared with the Paralithodes species, 

 which are primarily restricted to the continental shelf, L. couesi displays a variety of features which 

 appear to be adaptations for life in deeper water on the continental slope, including elongated legs, red 

 coloration, inflated branchial chambers, asynchronous spawning, and large eggs. Fecundity of 

 L.couesj increases asymptotically with carapace length according to the relationship £ = 4,329 - 3.19 

 X 10* e "'"^ . The size of 50% maturity is reached at 91.4 mm for males and at 80.2 mm for females. 



The deep-sea king crab, Lithodes couesi, is a little 

 known relative of the three species of king crab, 

 Paralithodes camtschatica, P. platypus, and L. 

 aequispina, commercially harvested in Alaska. 

 Since its original description (Benedict 1895), 

 L. couesi has been discussed only in taxonomic 

 works (Rathbun 1904; Schmitt 1921; Makarov 

 1938; Sakai 1971); other than its geographical 

 distribution (San Diego, Calif., to Onohama, 

 Japan) and depths of occurrence (542-1,125 m), 

 nothing has been reported concerning the life 

 history of this species. 



Considering its rather large size and conspic- 

 uous bright red color, it is surprising that L. couesi 

 has not received more attention. One reason for 

 this is that benthic sampling surveys infrequently 

 reach the depths inhabited by L. couesi, and those 

 that do typically are not designed to catch a large 

 number of specimens. However, in 1979 a National 

 Marine Fisheries Service (NMFS) cruise survey- 

 ing the commercial fishing potential of seamounts 

 in the Gulf of Alaska caught nearly 1,500 L. couesi 

 in large baited traps. The present study is based on 

 these specimens. 



Although L. couesi is unlikely soon to become 

 the target of a commercial fishery due to the great 

 depths it inhabits, the high value of crab and the 

 fluctuating supply of other Alaskan crab species 

 may stimulate technological developments mak- 

 ing deepwater crab fishing more economical. Such 

 developments have already occurred in the fishery 



'Contribution No. 539, College of Fisheries, University of 

 Washington, Seattle, Wash. 



^Center for Quantitative Science in Forestry. Fisheries and 

 Wildlife, University of Washington, Seattle, WA 98195. 



Manuscript accepted October 1980. 

 FISHERY BULLETIN: VOL. 79, NO. 2 



for another deepwater crab, Geryon quinquedens, 

 along the east coast of North America ( Wigley et 

 al. 1975). This paper is intended to provide a 

 comparison of life history characteristics between 

 L. couesi and shallow-water king crabs, as well as 

 to provide some information needed by fisheries 

 managers in the event L. couesi were to become 

 commercially important. 



METHODS 



Samples of L. couesi were collected between 31 

 May and 5 July 1979 on an NMFS stock assess- 

 ment cruise to eight seamounts located in the 

 central Gulf of Alaska (Figure 1). All specimens 

 except three were captured in baited traps. Three 

 types of trap were used: rectangular sablefish, 

 Anoplopoma fimbria, traps measuring 0.8 m x 

 0.8 m X 2.5 m and covered with 8.9 cm (bar 

 measure) webbing; conical sablefish traps mea- 

 suring 0.7 m high x 1.2 m base diameter x 0.9 m 

 top diameter and covered with 7.5 cm webbing; 

 and rectangular king crab traps measuring 1.8 m 

 X 1.8 m X 0.6 m and covered with 11.4 cm webbing. 

 Traps were arranged at 91.5 m intervals along a 

 1,006.5 m groundline having surface floats con- 

 nected to both ends. A typical set of gear included 

 four or five of each type of sablefish traps, plus two 

 king crab traps in 8 of the 25 sets. A total of 232 

 traps (102 conical, 114 rectangular, 16 king crab) 

 were set. Three small specimens of L. couesi were 

 obtained in one haul of a bottom trawl. 



All seamounts were extremely steep sided, ris- 

 ing approximately 3,000 m from the seafloor to 

 relatively flat summits composed of rock outcrops 



259 



1981. 



