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



885 



of discarded crabs would be high on the Argos Georgia, be- 

 tween 77% and 88% for both P. formosa and P. spinosissima 

 (77-84% for the former, 87-88% for the latter). On the Ar- 

 gos Helena discard survival rate was much lower, 50-58% 

 for P. formosa and 38-49% for P. spinosissima. 



Discussion 



Crab species 



Three previously unreported or rarely reported crab spe- 

 cies, Paralomis anamerae, NeoUthodes diomedeae (Bene- 

 dict, 1894), and Lithodes murrayi (Henderson, 1888), were 

 found in our study. The most abundant of these was P. ana- 

 merae, found at mid-range depths. The only other record of 

 P. anamerae is the original description of the species based 

 on four specimens obtained from the continental shelf of 

 Argentina at depths of 132-135 m (Macpherson, 1988). 

 The specimens obtained from South Georgia, at depths of 

 530-1210 m, therefore represent a considerable southerly 

 extension in the reported geographic distribution of this 

 species, as well as a notable increase in its bathymetric 

 range. Lopez Abellan and Balguerias (1994) reported both 

 P. spinosissima and P. formosa from a 1986-87 trawl survey 

 on the shelf, but no other species of crabs. 



A certain amount of confusion surrounds the identifica- 

 tion of Paralomis species around South Georgia. Paralomis 

 aculeata is found in the CCAMLR database, but almost cer- 

 tainly because of its inclusion in the FAO species identifica- 

 tion guide for the Southern Ocean CArnaud 1985, in Fischer 

 and Hureau, 1985), attributed to Henderson (1888). This 

 species is not mentioned in Macpherson (1988), even as 

 a junior synonym. Conversely, none of the Paralomis spe- 

 cies identified in the present paper appear in Fischer and 

 Hureau (1985). It is not clear, therefore, which species of 

 Paralomis CCAMLR scientific observers have been identi- 

 fying as P. aculeata. Twenty-two specimens ofN. diomedeae 

 were collected at depths ranging from 420 to 1294 m. This 

 species has previously been recorded from South Georgia 

 (Macpherson, 1988). 



Sixteen L. murrayi specimens were found on southeast 

 Shag Rocks and west South Georgia, approximately 60 nmi 

 apart, at depths of between 450 m and 605 m, Lithodes. 

 murrayi is mainly reported from the southern Indian 

 Ocean around Prince Edward, Crozet, and Possession 

 Islands, as well as Macquarie Islands, Mozambique Chan- 

 nel, and southern New Zealand at depths of 35-200 m 

 (Hale, 1941; Yaldwyn and Dawson, 1970; Arnauld, 1976; 

 Arnauld and Do-Chi, 1977; Kensley, 1977). However, it has 

 been reported in small numbers in CCAMLR statistical 

 catch records from 1993-94, 1997-98 and 1998-99 and 

 by CCAMLR observers (CCAMLRi). We have confirmed 

 the identification and the extension of the range of this 

 species to South Georgia. Klages et al. (1995) reported on 

 the distribution of L. murrayi off Peter Island, close to the 

 Antarctic continent between 180 and 260 m depth, and 

 a circum-Antarctic distribution has been claimed for the 

 species (Macpherson, 1988). The present study therefore 

 represents the greatest depth recorded for it. 



Distribution 



Catch rates of P. spinosissima encountered in our study 

 were lower than experienced in the September 1995-Janu- 

 ary 1996 crab fishery by the FV American Champion. Wat- 

 ters (1997) reported that average catch rates of legal-size 

 male P. spinosissima were between 14.2 and 28.4 males 

 per pot in the Shag Rocks and northwest South Georgia 

 areas (53.5-54°S, 37-40°W). Although the toothfish pots 

 operated by the Argos Georgia from March and May 2000 

 produced catch rates between 0.5 and 4 crabs/pot, the pro- 

 portion of legal-size males was very low (3%), resulting in 

 legal (retained) crab catch rates of less than 1/pot (note 

 that the retention rates given in Table 2 are lower than 

 those calculated from the length-frequency sampling. Fig. 

 6). Retention rates for the 1992 FV Pro Surveyor cruise 

 (July-August 1992) were 36% (Otto and Macintosh^). The 

 retention rates on the Argos Helena's experimental crab 

 fishery in 1999 were much lower than this (8% and 14% 

 for P. spinosissima and P. formosa respectively) (Purves^). 

 The low retention rate is most likely to be a consequence 

 of the pot design used on vessels G and H, where the col- 

 lapsible funnel entrances might have restricted the catch 

 to smaller size crabs. 



A further feature of the American Champion crab fishery 

 was the restriction of fising effort to depths of less than 500 

 m. The present trials were targeted at toothfish rather than 

 crabs and were conducted according to an experimental 

 plan that distributed fishing effort over time, area, and 

 the full depth range of longlines used in the main toothfish 

 fishery. Accordingly, fishing occurred over a much wider 

 depth range than was used by the previous crab fisheries. 

 Our very high catch rates of P formosa in deep water were 

 therefore not reported by Watters (1997). However, even 

 our catch rates did not result in high numbers of retained 

 legal-size crabs on the Argos Georgia because the propor- 

 tion legally permitted was only 10.5%. Interestingly, even 

 in shallow water (400-800 m) P. formosa appeared to be 

 more common than P. spinosissima. Only in waters less 

 than 400 m deep did P. spinosissima become the dominant 

 species. This finding confirms the results of Watters (1997) 

 who found that P. spinosissima catch rates declined at 

 depths deeper than 300 m. Catch rates of P. spinosissima 

 were low even in these depths (5 crabs/pot). Only 9 of the 

 total of 110 sets of the Argos Georgia were conducted in 

 depths shallower than 400 m because the main target of 

 the fishery was toothfish. 



The differences found in our study in the distribution 

 by depth of the different sexes and sizes of crabs might 



■^ Otto, R. S., and R. A. Macintosh. 1992. A preliminary report 

 on research conducted during experimental crab fishing in 

 the Antarctic during 1992 (CCAMLR Area 48). Document 

 WG-FSA-92/29, 20 p. CCAMLR, RO. Box 213, North Hobart, 

 Tasmania, Australia. 



* Purves. M. G. 1999. Report of the South African designated 

 CCAMLR observer on board the British registered longliner 

 "Argos Helena" in Statistical Subarea 48.3, 31 August to 23 

 September 1999, 13 p. CCAMLR, RO. Box 213, North Hobart, 

 Tasmania, Australia. 



