The marine pelagic system around South Georgia is characterised by considerable inter-annual variability which is linked to large-scale climate variability, indicated and probably mediated by local oceanographic and atmospheric conditions. Much of the observed variability in various fitness metrics for birds, seals and fish seems to be connected with the availability of Antarctic krill, Euphausia superba, which is a major prey species for many vertebrate populations at South Georgia. The marine ecosystem at South Georgia is the focus of a major research effort and consequently there are many sources of data available indicating its state. These include remotely-sensed satellite data, fishery data, surveys of krill and mackerel icefish, and monitoring of land-based predators. Each of these data sources revealed a strong anomaly in early 2009. Above average sea temperatures, without any evidence of increased warm water inflow were followed by reduced icefish catches, a paucity of krill in icefish and penguin diets and low krill biomass in the regularly surveyed “Western Core Box”. Consequently many of the nominally “krill dependent” populations of land based predators produced under-weight offspring and the combined standardised index of CCAMLR ecosystem monitoring programme data from Bird Island reached its lowest level in over two decades of monitoring. These observations provide support for the idea that krill is a major mediator of climatic effects on the ecosystem. They also suggest that icefish diets, in addition to metrics from land-based predators, can provide a useful and, potentially, early indication of krill availability.
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