LENGTH-WEIGHT RELATIONSHIPS OF 



BLUE, PARALITHODES PLATYPUS, AND GOLDEN, 



LITHODES AEQUISPINA, KING CRABS PARASITIZED BY 



THE RHIZOCEPHALAN, BRIAROSACCUS CALLOSUS BOSCHMA 



Clayton R. Hawkes, Theodore R. Meyers, and Thomas C. Shirley 1 



ABSTRACT 



Length-weight relationships and condition factors of nonparasitized blue king crabs, Paralithodes platypus, 

 and golden king crabs, Lithodes aequispina, in southeastern Alaska were compared with crabs parasi- 

 tized by the rhizocephalan, Briarosaccus callosus. Species, sex, and shell condition were considered in 

 all analyses. Parasitized male blue king crabs and parasitized male golden king crabs weighed significant- 

 ly less than nonparasitized individuals. Golden king crabs may be more resistant to infection and the ef- 

 fects of B. callosus parasitism than blue king crabs. They had a lower prevalence of infection, and the 

 percent difference between the body mass of parasitized and nonparasitized crabs was considerably less. 

 In both crab hosts the prevalence of infection was greater in samples where sublegal or smaller size classes 

 of adults were included in analyses, suggesting that crab growth was reduced by the parasite 



A parasite of lithodid crab species in Alaska is the 

 rhizocephalan barnacle, Briarosaccus callosus 

 Boschma (Boschma and Haynes 1969; Boschma 

 1970; McMullen and Yoshihara 1970; Somerton 1981; 

 Hawkes et al. 1985). The parasite's distribution in 

 Alaskan waters, its life history, and its effects on 

 king crab hosts are almost unknown except that 

 parasitized crabs become castrated (Boschma and 

 Haynes 1969; McMullen and Yoshihara 1970). The 

 prevalence of this barnacle parasite varies between 

 areas and species and is especially high in south- 

 eastern Alaska. Parasitism by B. callosus might 

 decrease the productivity of king crab stocks 

 through sterilization and may also reduce crab 

 growth rates. Therefore, parasitized crabs of the 

 same size as nonparasitized crabs may weigh less. 

 In this study we examined the influence of B. callosus 

 on the length-weight relationships and condition fac- 

 tors of parasitized and nonparasitized blue king crab, 

 Paralithodes platypus, and golden king crab, Li- 

 thodes aequispina. 



MATERIALS AND METHODS 



Two methods were used to compare the growth of 

 parasitized and nonparasitized crabs. A Fulton's con- 

 dition factor (w/l s x 10 ~ 4 , where w = weight in 

 grams and I = carapace length in mm) was used for 



'School of Fisheries and Science, University of Alaska, Juneau, 

 11120 Glacier Highway, Juneau, AK 99801. 



comparing different individuals of the same species 

 (Ricker 1975). This method assumes that all body 

 parts grow isometrically. The second method used 

 for comparison assumes allometric growth, where 

 different body parts grow at different rates. Con- 

 stants were determined empirically by linear regres- 

 sion using the model, w = AL B , and logarithms of 

 the carapace lengths and body weights (Everhart et 

 al. 1976, p. 70-71). The length-weight relationships 

 of parasitized and nonparasitized crabs were com- 

 pared with analysis of covariance (ANCOVA). All 

 mean values (X) are given ± 1 standard deviation. 

 Probabilities <0.05 are considered significant and 

 those <0.01 are considered highly significant. 



The analysis of length-weight relationships was 

 based on wet weights taken in the field (nearest 25 

 g) and in the laboratory (nearest gram). Crabs with 

 missing or partially regenerated appendages were 

 not weighed. Carapace lengths were measured to the 

 nearest 1 mm (Wallace et al. 1949). Shell condition 

 was classified according to a four point scale (Somer- 

 ton and Macintosh 1983). A new shell condition is 

 found in crabs that have recently molted, and skip- 

 molt crabs are those that have not molted within the 

 last year. Skipmolts or old shell crabs were identified 

 by worn spines and dactyl tips and accumulations 

 of shell epifauna. Infections were diagnosed gross- 

 ly by the presence of externae or scars, indicative 

 of lost externae. A scar is a short chitinous brown 

 pedicel from which an externa was attached and pro- 

 trudes from underneath the abdomen. 



Manuscript accepted July 1985. 



FISHERY BULLETIN: VOL. 84, NO. 2, 1986. 



327 



