INTERANNUAL VARIABILITY IN KRILL ABUNDANCE AT SOUTH GEORGIA

Interannual variability within the pelagic marine environment around S outh Georgia is a well-recognised phenomenon. A key aspect of this var iability is interannual fluctuation in the abundance of Antarctic kril l Euphausia superba. Here we describe a new acoustic survey programme to monitor krill abundance in the South Georgia region. We present bio mass estimates for 2 survey boxes, located over the shelf-break to the northeast and northwest of the island, derived from the first of thes e surveys conducted in January 1996. We contrast these with the most r ecent previous estimates for the region obtained in January 1994. Weig hted mean krill density (and weighted variances) estimates for the 199 6 surveys were 40.57 g m(-2) (13.37) and 26.48 g m(-2) (54.30) for the eastern and western boxes respectively These are high compared with t hose obtained in January 1994, when estimates for similar areas were 1 .87 g m(-2) (0.14) and 7.43 g m(-2) (1.33) respectively. The greater t han 20-fold difference between surveys reveals a very large interannua l variability in krill abundance at South Georgia. In 1994 the low abu ndance resulted in greatly reduced breeding success in most habitual k rill predator species there. In the 1996 season, however, breeding suc cess of these species was normal. Instantaneous estimates of krill abu ndance using acoustic techniques are therefore consistent with measure ments from predators, whose breeding performances provide a longer-ter m indication of prey abundance in the surrounding pelagic ecosystem in a particular season.