The trade volume currently exceeds 30 trillion ton-miles and is growing at a rate faster than the global economy ( United Nations Conference on Trade and Development 2007). In 2006, 7.4 billion tons of goods were loaded at the world's ports. According to estimates, as much as 90 per cent of world trade is hauled by ships ( International Maritime Organization 2006). Among the different means of transport, ocean shipping stands out as the most energy efficient mode of long-distance transport for large quantities of goods ( Rodrigue et al. The ability to travel, trade commodities and share information around the world with unprecedented efficiency is a defining feature of the modern globalized economy. The data analysed in this paper improve current assumptions based on gravity models of ship movements, an important step towards understanding patterns of global trade and bioinvasion. The network of all ship movements possesses a heavy-tailed distribution for the connectivity of ports and for the loads transported on the links with systematic differences between ship types. Container ships follow regularly repeating paths whereas bulk dry carriers and oil tankers move less predictably between ports. These three categories do not only differ in the ships' physical characteristics, but also in their mobility patterns and networks. In particular, most ships can be classified into three categories: bulk dry carriers, container ships and oil tankers. We show that the network has several features that set it apart from other transportation networks. Here, we use information about the itineraries of 16 363 cargo ships during the year 2007 to construct a network of links between ports. With 90 per cent of world trade carried by sea, the global network of merchant ships provides one of the most important modes of transportation. Transportation networks play a crucial role in human mobility, the exchange of goods and the spread of invasive species.
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