468 



Fishery Bulletin 92(2), 1994 



Differences in pelagic red crab 

 chemical composition 



The lipid content of the younger 

 stranded pelagic red crabs was dif- 

 ferent from that recorded in older 

 specimens caught on the benthos of 

 the continental shelf (Table 1). Dif- 

 ferences in the proportion of chemi- 

 cal components between young and 

 old individuals have been reported 

 for many decapod species (Herring, 

 1973; Morris, 1973). The observed 

 differences in lipid concentration and 

 apparent pigmentation between 

 young-adult and older-benthic pe- 

 lagic red crabs cannot be considered 

 abnormal or attributable to un- 

 healthy specimens. There was no evi- 

 dence to support the hypothesis of a 

 debilitated fraction of pelagic red 

 crabs, and strandings can be ex- 

 plained by mere accident. 



The differences in lipid and ash 

 content between male and female 

 stranded crabs would be attributable 

 to metabolic differences in which fe- 

 males require more lipid to invest in 

 egg production (Hartnoll, 1985). 

 Some females still had eggs attached 

 on the pleopods as evidence of their repro- 

 ductive condition; however, the low numbers 

 of ovigerous females in the sample, suggested 

 that we collected them at the end of the 

 breeding season. 



Size and sex of pelagic 

 stranded red crabs 



The stranded individuals we sampled were 

 predominantly 13 to 20 mm SCL, although 

 some larger crabs were also found (Fig. 3). 

 Kato ( 1974) also reported individuals of these 

 two size distributions in a mass stranding in 

 Bahia Magdalena. Photos were available of 

 a mass stranding in May of 1979, in which 

 pelagic red crabs larger than 25 mm SCL 

 (second year of life, Boyd 1962) were very 

 abundant. Therefore, the over-representation 

 of young adults in the 1991 stranding we 

 sampled is not the rule, as both size and age 

 groups were found. 



The sex ratio (1:1.11) of our sample was 

 significantly female biased (P<0.05, x 2 =22.97, 

 df=l,147). Benthic samples of crabs in Bahia 

 Magdalena during 1990 (Soli's, 1991), also 



> 

 o 



z 



LU 

 D 



o 



LU 



350 



300 



250 



200 



150 



100 



50 



1150 



14 



n = 724 



hk 



12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 

 STANDARD CARAPACE LENGTH mm 



B STRANDED CRABS \^J BENTHIC CRABS 



Figure 3 



Size distribution of pelagic red crabs, Pleuroncodes planipes, 

 stranded in Bahia Magdalena and the typical distribution of 

 benthic crabs on the continental shelf off Baja California. 



