in fish stocks has led to the rise of aquaculture, including fish farming both on the coasts and in the interior. Mining Despite the general poor returns in recent years, mining retains a certain importance in Andalusia. Andalusia produces half of Spain's mining product by value. Of Andalusia's production, roughly half comes from the province of Huelva. Mining for precious metals at Minas de Riotinto in Huelva (see Rio Tinto Group) dates back to pre-Roman times; the mines were abandoned in the Middle Ages and rediscovered in 1556. Other mining activity is coal mining in the Guadiato valley in the province of Córdoba; various metals at Aznalcóllar in the province of Seville, and iron at Alquife in the province of Granada. In addition, limestone, clay, and other materials used in construction are well distributed throughout Andalusia. Secondary sector: industry The Andalusian industrial sector has always been relatively small. Nevertheless, in 2007, Andalusian industry earned 11.979 million euros and employed more than 290,000 workers. This represented 9.15 percent of regional GDP, far below the 15.08 the secondary sector represents in the economy of Spain as a whole. By analyzing the different subsectors of the food industry Andalusian industry accounts for more than 16% of total production. In a comparison with the Spanish economy, this subsector is virtually the only food that has some weight in the national economy with 16.16%. Lies far behind the manufacturing sector of shipping materials just over 10% of the Spanish economy. Companies like Cruzcampo (Heineken Group), Puleva, Domecq, Santana Motors or Renault-Andalusia, are exponents of these two subsectors. Of note is the Andalusian aeronautical sector, which is second nationally only behind Madrid and represents approximately 21% of total turnover in terms of employment, highlighting companies like Airbus, Airbus Military, or the newly formed Aerospace Alestis. On the contrary it is symptomatic of how little weight the regional economy in such important sectors such as textiles or electronics at the national level. Andalusian industry is also characterized by a specialization in industrial activities of transforming raw agricultural and mineral materials. This is largely done by small enterprises without the public or foreign investment more typical of a high level of industrialization. Tertiary sector: services In recent decades the Andalusian tertiary (service) sector has grown greatly, and has come to constitute the majority of the regional economy, as is typical of contemporary economies in developed nations. In 1975