Management and Ecological Note Direct effects of climate change on the Antarctic krill ﬁshery S. KAWAGUCHI & S. NICOL Australian Antarctic Division, Department of the Environment, Water, Heritage and the Arts, Kingston, Tas., Australia A. J. PRESS Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tas., Australia Climate change is predicted to affect marine ﬁsheries, but these effects are usually considered to be indirect, for example through distributional changes in ﬁsh populations (Perry, Low, Ellis & Reynolds 2005), changes in marine biodiversity (Cheung, Lam, Sarmiento, Kearney, Watson & Pauly 2009) or changes in oceanic productivity (Sharp 2003). This article shows that in Antarctic waters, there is already evidence of direct eﬀects of the changing physical environment – the duration of sea ice cover – on the seasonal behaviour of the regionÕs largest ﬁshery, that for Antarctic krill, Euphausia superba (Kock, Reid, Croxall & Nicol 2007). Declining sea ice cover in the main krill ﬁshing grounds has resulted in greater accessibility of krill stocks to the ﬁshing ﬂeets, partic- ularly during winter, and this change in ﬁshing behaviour will need careful management in an era of rapid ecological change. The ﬁshery for Antarctic krill is the largest in tonnage in the Southern Ocean, and managed by Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), taking an annual catch of 120 000 t yr )1 from three ﬁshing grounds in the South Atlantic (Kock et al. 2007). The internationally agreed precautionary catch limits for the krill ﬁshery total some 6.55 million tonnes making this ﬁshery one of the few ﬁsheries worldwide that is currently exploited far below its sustainable level (Kock et al. 2007). The key role of krill in the Antarctic ecosystem has required a precautionary approach to management of the harvesting of this species, but this management approach is yet to take into account the eﬀects of a changing climate (Kock et al. 2007). Over the four decades during which the krill ﬁshery has been operating, there has been a distinct pattern of opera- tion of the ﬁshing ﬂeets in the three ﬁshing grounds in the South Atlantic: South Georgia, the South Orkney and the South Shetland Islands (Fig. 1). Fishing operations in Antarctic waters are primarily aﬀected by ice conditions. The South Georgia ﬁshing grounds are always ice free in winter and summer thus permitting year-round exploitation, the South Orkney generally have a longer ice-free season than the South Shetland, thus the potential ﬁshing season has been more constricted towards the south (Fig. 1) (Kawag- uchi, Nicol, Taki & Naganobu 2006; Kawaguchi & Nicol 2007). In recent years, especially during the last two decades, the winter ice conditions in the South Atlantic have been benign, showing a signiﬁcant negative trend in annual ice cover index (y = 0.0518x + 107.67; r 2 = 0.22, P < 0.05). Consequently, the krill ﬁshing ﬂeet has been able to remain in the south of the ﬁshing grounds, especially in the South Shetland Islands area, for a much greater part of the year (Fig. 2), thus catches from this region have continued throughout winter in some recent years. The longer ﬁshing season towards the south may also be associated with a possible shrinkage of the overall distribution of krill range as a result of climatic warming (Siegel 2005). Although no trends were observed between sea ice index and the duration of ﬁshing operations when each Correspondence: So Kawaguchi, Australian Antarctic Division, Department of the Environment, Water, Heritage and the Arts. Channel Highway, Kingston, Tas. 7050, Australia (e-mail: so.kawaguchi@aad.gov.au) Fisheries Management and Ecology, 2009, 16, 424–427 doi: 10.1111/j.1365-2400.2009.00686.x Ó 2009 Commonwealth of Australia. Fisheries Management and Ecology