Purves et al.: Distribution, demography, and discard mortality of crabs caught as bycatch in the South Atlantic 



879 



value often dominated catches. Only about 38% of 

 P. spinosissima sampled between 200 and 400 m 

 were males, whereas this proportion increased to 

 about 76% in depths of 600 to 800 m (Fig. 4). The 

 mean carapace width of males remained relatively 

 constant between 200 to 800 m, but female P. spi- 

 nosissima decreased in size with an increase in 

 depth (Fig. 5). 



Size frequencies 



Males achieved larger sizes than females in all 

 three species (Fig. 6). Only 5.7% of the sampled 

 P. spinosissima individuals were of legal size 

 (carapace width greater than 102 mm), of which 

 only 6% were females. A difference was also noted 

 in the percentage of legal-size P. spinosissima for 

 the different areas: 10% at South Georgia and 

 only 3.8% at Shag Rocks. For P. formosa only 

 11.6% (/! = 1012) were larger than the minimum 

 legal size of 90 mm. Of these legal crabs only 6%- 

 (n=63) were females, indicating that few females 

 would be processed if carapace width was the only 

 criterion used to select crabs that could be taken 

 legally. No obvious difference was noted in the 

 percentage of legal-size crabs caught in the two 

 main fishing areas. 



Although a legal-size limit is not specified for P. 

 anamerae (sizes ranged from 39 to 96 mm), only 

 two crabs (0.2% of sample) were larger than the 

 legal limit for P. formosa (90 mm). A peak in the 

 length distribution of this species occurred be- 

 tween 55 and 57 mm, and few crabs were larger 

 than 77 mm. 



Differences in the size-frequency distribution 

 of the sexes was more pronounced for P. formosa 

 than for the other two species; females peaked at 

 65-72 mm and males peaked at between 85 and 

 90 mm carapace width (Fig. 6). For P. spinosissima 

 female size distribution peaked between 78 and 82 

 mm and males peaked at 87 to 92 mm carapace 

 width (Fig. 6). Males and females of P. anamerae 

 had a relatively even size distribution up to cara- 

 pace widths of 65 mm. Most of the larger crabs 

 were males; only 6.8% of individuals larger than 

 65 mm were females. Maximum widths recorded 

 were 121 mm (P. spinosissima), 120 mm {P. for- 

 mosa), and 91 mm (P. anamerae). 



Size at maturity 



There was no significant difference between 

 female size at maturity at Shag Rocks and South 

 Georgia for either species (^-tests on Sm^g esti- 

 mated by fitting logistic models to the proportion 

 mature at size, P>0.05). The close allometric 

 relationship found between carapace width and 

 length (Table 4) made it possible to alter between these two 

 types of measurements (Table 5). Combining the two areas, 

 female size at maturity was 55.1 mm carapace length 



200 300 400 500 600 700 800 

 Depth (m) 

 — P formosa - -*- - P spinosissima. EG 



900 1000 1100 1200 



.fi.  . P spinosissima. SR 



Figure 3 



General-linear-model-predicted CPUE (numbers per pot) for the 

 two species (Paralomis formosa and P. anamerae) at different depths 

 standardized for a soak time of 18 h (the average used in the study). 

 For P. spinosissima predictions at East South Georgia and Shag Rocks 

 are presented separately (EG, SR, respectively). 



n = 1988 



80 



70  



60 - 



50 



40 



30 



20 



10 



% IVIales of P formosa 



% IVIales of P spinosissima 



200-400 400-600 600-800 



800- 

 1,000 



1 ,000- 

 1,200 



1,200- 

 1,400 



Depth range (m) 



Figure 4 



The percentage of males of Paralomis formosa and P. spinosissima 

 found at different depth ranges during random sampling of the crab 

 bycatch; all data from cruises Gl (Argos Georgia cruise 1), G2 (Argos 

 Georgia cruise 2), and H (Argos Helena cruise) were used. 



(57.1 mm carapace width) for P. formosa and 61.2 mm 

 carapace length (67.7 mm carapace width) for P. spinosis- 

 sima (Fig. 7). These sizes are very similar to the 61.7 mm 



