This map shows 35 large refrigerated cargo ships (reefers) operating in 2013 in western African waters:
Each orange spot marks a point where the ship has emitted a signal.
A high density of signals generates a hotspot, identified by a circle. This marks a point where the ship has either switched off its engine or has reduced its cruising speed to a maximum of 1 knot (1 UK nautical mile/hour). This visualisation includes only hotspots at a minimum distance of 6 nautical miles from any port.
Each country's Exclusive Economic Zone (EEZ) border is marked by a thin grey line.Transhipment (moving catches from small fishing boats to reefers) in the EEZs of Senegal and Côte d'Ivoire is prohibited.
A reduced number of reefers, for example Izar Argia, are lacking in good enough signals for brief periods of time, in a way that their itineraries seem to cross over some peninsulas' tips by land.
The Meltemi's and Dolly 798's AIS signals have not enough quality to show a coherent pattern, so the authors decided not to include them in the visualisation.
What are we looking out for?
Straight lines and uniform, regular tracks indicate that ships are crossing an EEZ at cruise speed.
A higher frequency of hotspots and an erratic track pattern indicates that ships are operating in a specific area – and potentially seeking out fish transhipment business. (Sometimes however a hotspot is generated by the vessel simply waiting for instructions and changing direction, which is a normal manoeuvre.)
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