Ecology of an exploited Antarctic fish community
Demersal fish represent one of the most heavily exploited resources in the Antarctic ecosystem. Fish stocks around South Georgia Island have contributed a substantial portion of the annual catches and have declined over the past decade. Fishing has been implicated as the cause of this decline. However, a clear description of the fish community's structure and function, which is considered necessary to accurately judge the influence of fishing, has been lacking to date. The distributions and abundances of the species present in the South Georgia system were used to examine the spatial structure and temporal consistency of that Antarctic fish community. The analyses of 1987-88 and 1988-89 surveys of these stocks are described. The results did not show any evidence for the recovery of these depleted stocks. Gut contents of fish collected in 1987-88 were used to describe the trophic structure and connections within the community. Three distinct trophic groups were identified: krill-eaters, piscivores, and generalists. The prevalent role of the krill resource in this community was demonstrated. However, there was little evidence for strong competition between species. The species composition of the community was tested for change by application of a Monte Carlo simulation technique. The results revealed a statistically significant shift in the community from 1986-87 to 1987-88. The trend was one of increased equitability between species abundances. Investigation of community spatial structure indicated a basic lack of such structure. Weak structure revealed by the initial analysis was due to the presence or absence of rare species. The absence of strong structure was consistent from year to year. The reasons for this lack of spatial structure were unclear. All surveys were conducted during the austral summer. Conditions at other times of the year were unknown. A decrease in the availability of resources during the winter may possibly cause a seasonal bottleneck, resulting in increased competition and community structure. More extensive sampling, expanded to include other seasons, is necessary to properly address the questions of seasonal change in community structure and the role of competition in this Antarctic system.
James Edward McKenna,
"Ecology of an exploited Antarctic fish community"
Dissertations and Master's Theses (Campus Access).