poor soil. Today, the mix of cereals and vegetables grown is similar to that of the UK as a whole, but only a minority of land is arable. Only 32% of Northern farmland is primarily used for growing crops, compared to 49% for England as a whole. Conversely, 57% of the land is given over to rearing livestock, and 33% of England's cattle, 43% of its pigs and 46% of its sheep and lambs are reared in the North. The only part of the region that is predominantly given over to crops is the land around the Humber estuary, where the well-drained fens result in excellent quality land. The lowland Cheshire Plain is mostly given over to dairy farming, while in the Pennines and Cheviots grazing sheep play an important role not just in agriculture but also in land management more generally. Heather moorland in the Pennine uplands is home to driven grouse shooting from 12 August (the Glorious Twelfth) until 10 December every year. The number of grouse moors in Northern England is a major threat to natural predators, which are often killed by gamekeepers to protect grouse, and as a result, the Cumbria Wildlife Trust describes the North's moors as a "black hole" for the endangered hen harrier. Sea fishing is an important industry for Northern coastal towns. Major fishing ports include Fleetwood, Grimsby, Hull and Whitby. At its height, Grimsby was the largest fishing port in the world, but the Northern fishing industry suffered greatly from a series of events in the second half of the twentieth century: the Cod Wars with Iceland and establishment of the exclusive economic zone ended British access to rich North Atlantic fishing grounds, while the North Sea was badly overfished and the European Common Fisheries Policy put strict quotas on catches to protect the almost depleted stocks. Grimsby is now transitioning to the processing of imported seafood and to offshore wind to replace its fishing fleet. Manufacturing and energy Northern England has a strong export-based economy, with trade more balanced than the UK average, and the North East is the only region of England to regularly export more than it imports. Chemicals, vehicles, machinery and other manufactured goods make up the majority of Northern exports, just over half of which go to EU countries. Major manufacturing plants include car plants at Vauxhall Ellesmere Port, Jaguar Land Rover Halewood and Nissan Sunderland,