Margaret River is the foremost Geographical Indication wine region in the South West Australia Zone, with nearly 5,500 hectares under vine and over 138 wineries as at 2008. Margaret River wine region is made up predominately of boutique size wine producers; although winery operations range from the smallest crushing 3.5 tonne per year to the largest around 7000 tonne. The climate of Margaret River is more strongly maritime-influenced than any other major Australian region. It has the lowest mean annual temperature range, of only 7.6C, and for good measure has the most marked Mediterranean climate in terms of rainfall, with only 200 millimetres of the annual 1160 millimetres falling between October and April. The low diurnal and seasonal temperature range means an unusually even accumulation of warmth. Overall the climate is similar to that of Bordeaux in a dry vintage. Although the region produces just three percent of total Australian grape production, it produces over 20 percent of Australia's premium wine market. The principal grape varieties are fairly evenly split between red and white; Cabernet Sauvignon, Chardonnay, Sauvignon Blanc, Sémillon, Shiraz, Merlot, Chenin Blanc and Verdelho.