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By current definition, a VMS programme monitors fishing vessels that have VMS units installed. In this context, a limitation of VMS is that vessels without installed VMS units or vessels with faulty VMS units are not being monitored. In many cases, illegal fishing may be conducted by these vessels. Remote sensing by imaging satellites and other technologies may offer partial solutions to this limitation.

Satellite Remote Sensing

Satellites are used for a variety of commercial and governmental imaging purposes. Imaging satellites can detect vessels either optically or by synthetic aperture radar (SAR). Satellite imagery can potentially detect all fishing vessels, i.e. those with shipboard VMS units, those without VMS units, and those with faulty VMS units. It is important to note the distinction between detecting vessels and identifying them. Most current satellite imaging technology does not allow the identification of vessels.

Optical imaging currently offers higher resolution than SAR, and could be used to detect vessels that are marked with their identification. Many countries follow the guidelines contained in the FAO  (no link available) , where a vessel displays its radio call sign on a horizontal surface of the vessel. Optical imaging is, however, strongly affected by cloud cover and darkness, and comes at a higher cost, so it is not being widely evaluated for use in fisheries management.

Synthetic aperture radar technology has recently begun to be evaluated for application to fisheries monitoring. Early results indicate that SAR imaging may have a role in the future of fisheries monitoring. For widespread application of remote sensing in vessel characterization, the science and art of image processing and interpretation need further development, and additional means for vessel identification are required.

Beyond the current limitations, satellite imaging might be useful for remote monitoring of areas or fisheries where traditional surveillance methods and VMS are not feasible. Also, the combined use of a VMS and satellite imaging could be more effective than a VMS alone. The VMS could identify participating vessels, and managers could focus their interest on vessels detected, but unidentified, by the satellite imagery.

Radar and Sonar

Other remote surveillance methods could also be useful in combination with VMS programme. The coverage and effective range of these systems tend to be localized, but radar (land or sea-based) and sea-based sonar systems have been used for the remote detection of vessels. As with satellite imaging, these tools may detect vessels, but may not identify them.


Several agencies and companies have experience with developing satellite detection of vessels (Note: FAO provides these links as an educational courtesy to readers, and does not endorse or promote any particular agency or company):

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