Trophic Relationships within the Antarctic Demersal Fish Community

Graduate School of Oceanography. University of Rhode Island Narragansett. Rhode Island 02882 Present address: Florida Marine Research Institute 100 8th Avenue SE. St. Petersburg. Florida 33701 Trophic Relationships within the Antarctic Demersal Fish Community of South Georgia Island Abstract.Knowledge of trophic relationships is vital to understanding any ecological community. The trophic relationships of Antarctic demersal fish are poorly known and have been described quantitatively by only a few researchers. Gut contents were analyzed on over 300 stomachs from fish collected during the 1987-88 AMLR ground fish survey of South Georgia I., Antarctica. All fish were collected with a bottom trawl during the austral summer. Fifteen species of demersal fish (including those of commercial value) were collected. Similarity analysis was applied to the diet information to describe trophic relationships in the South Georgia community. The most abundant species of the South Georgia demersal fish community were classified into three groups based on summer diets. The largest group contained species heavily dependent on krill Euphausia superba, and included Champsocephalus gunnm'i and Notothenia rossii. The second group was comprised of piscivores. Three of the four members of this group (Dissostichus eleginoides, Chaenocephalus aceratw3, and Pseudochaenichthys georgianus) are commercially valuable. The food of their prey often consisted of krill. The third group contained a loose association of species which feed on benthic organisms more than did other fish species in the community. Notothenia gibberifrons and Notothenia. squa.mifrons were the important commercial species in this group. Krill was found to be the most important prey species to the fish in the South Georgia system. However, based on the analysis of diet overlap, competition appeared to be unimportant in this community during the austral summer. Selective reduction of populations within the fish community by fishing may have widespread repercussions. Many of the commercially valuable species feed on other fish species which in turn feed on krill or benthic organisms. The relatively simple but highly interconnected food web in the South Georgia system may have a lower potential for fish yield than previously thought.