AbStfclCt.— Demersal fish repre- 

 sent one of the most heavily ex- 

 ploited resources in the Antarctic 

 ecosystem. The stocks around South 

 Georgia Island have contributed a 

 substantial portion of the annual 

 catches and have declined over the 

 past decade. Fishing has been im- 

 plicated as the cause of this decline. 

 However, a clear description of the 

 community structure of this system, 

 which is necessary to judge the in- 

 fluence of fishing accurately, has 

 been lacking. 



The spatial structure of the South 

 Georgian fish community was inves- 

 tigated through the use of survey 

 data collected over a three-year pe- 

 riod. The results clearly indicated 

 the absence of spatial structure in 

 that community. The presence or ab- 

 sence of rare species at various sta- 

 tions was responsible for the weak 

 structure found in the initial analy- 

 sis. The general lack of structure was 

 consistent from year to year. 



The available data do not provide 

 an explanation for this lack of struc- 

 ture. All surveys were conducted 

 during the austral summer only. 

 Events and community structure at 

 other times of the year remain un- 

 known. Although the data were rep- 

 resentative of the fish community 

 during the austral summer, no com- 

 parable data were available on the 

 abundance and distribution of their 

 prey items, especially krill (JEuphau- 

 sia superba). More extensive sam- 

 pling, expanded to include other 

 seasons, is necessary to properly ad- 

 dress the questions of seasonal 

 change in community structure and 

 the role of competition in this Ant- 

 arctic system. 



Spatial structure and temporal 

 continuity of the South Georgian 

 Antarctic fish community 



James E. McKenna Jr. 



Graduate School of Oceanography. University of Rhode Island. Narragansett. Rl 02882 



Present Address. Florida Marine Research Institute. 100 Eighth Ave S.E. 

 St Petersburg, FL3370! 



Manuscript accepted 11 May 1993. 

 Fishery Bulletin 91:475-490 1 1993). 



The marine systems of the Antarctic 

 are important both ecologically and 

 economically. Many of the seasonal 

 and long-term events that occur in 

 this region have a significant impact 

 on global environmental conditions 

 (Gordon, 1975; Broecker and Peng, 

 1982; Kennett 1982, p. 249). The Ant- 

 arctic is a large region physically iso- 

 lated from the rest of the globe by 

 the circumpolar circulation of the 

 West Wind Drift Current (Kennett 

 1982, p. 725). The organisms of the 

 Southern Ocean are unique and of- 

 ten highly productive. The waters 

 south of the Antarctic convergence 

 (about 5% of the world ocean) con- 

 tribute a total production equivalent 

 to 209c of that produced by all the 

 oceans of the world (El-Sayed, 1968). 

 In fact, it is believed that the evolu- 

 tion of the Mysticeti (baleen whales) 

 depended on the development of 

 the great production of this area 

 (Fordyce, 1977). 



The environment of Antarctica and 

 its associated islands has been es- 

 tablished for a long time (ca. 37 mil- 

 lion years), allowing a group of 

 perciform fishes to radiate into a va- 

 riety of niches and to dominate the 

 fish fauna of this highly productive 

 region (DeWitt, 1971; Targett, 1981; 

 Eastman, 1985). Like other polar 

 communities it is one of low species 

 richness (Hedgepeth, 1969; Everson, 

 1984). Over 70% of the species and 

 90% of the individuals belong to four 

 families in the suborder Nototheni- 

 oidei and 95*7 of the species in this 

 group are endemic to the Antarctic 



region (DeWitt, 1971). The four domi- 

 nant families are the Antarctic cods 

 (Nototheniidae), dragonfish (Bathyd- 

 raconidae), icefish (Channichthyidea), 

 and plunderfish (Harpagiferidae). 

 These fish are generally sedentary, 

 benthic forms found on the Antarctic 

 continental shelves (Targett, 1981). 

 Many of the species in this group 

 have evolved to fill niches usually oc- 

 cupied by different families or orders 

 offish (Eastman, 1985). 



Large stocks of demersal fish were 

 discovered around some of the islands 

 of the Scotia Arc in the late 1960s 

 (Kock, 1986). A relatively intense and 

 successful fishery developed around 

 these stocks, especially those found 

 at South Georgia Island (Fig. 1). 

 However, the decline of those stocks 

 over the past two decades has been 

 evident (Kock, 1985a, 1986; Gabriel, 

 1987; McKenna and Saila, 1989; 

 McKenna 1 ). This is especially true for 

 the target species of this fishery, the 

 marbled rockcod iNotothenia rossii) 

 and the mackerel icefish (Champ- 

 socephalus gunnari). There is also 

 evidence that a short-term (two to 

 three years) shift in the species as- 

 semblage inhabiting the continental 

 shelf around South Georgia has oc- 

 curred (McKenna and Saila, 1991). 



Although overfishing is suspected 

 as the cause of the changes observed 



'McKenna, J. 1990. Status of the stocks of Ant- 

 arctic demersal fish in the vicinity of South 

 Georgia Island. January 1989. Antarctic Mar. 

 Living Res. Contract Rep. Available from Dr. 

 R. Holt, NOAA, NMFS, Southwest Fisheries 

 Sci. Center, La Jolla, CA 92038. 



475 



