By Tia Jordan, Fisheries Analyst at OceanMind
Situated in the South Atlantic Ocean, Tristan da Cunha is the most remote inhabited archipelago in the world. Part of the UK Overseas Territories, Tristan da Cunha’s 750,000-km2 Exclusive Economic Zone (EEZ) is closed to commercial fishing, with exception to those granted a licence issued under the provision of the Fishery Limits Order.
The remote nature of the islands and the large EEZ make protecting against Illegal, Unreported and Unregulated (IUU) fishing a real challenge. It is only through the use of satellite technology that detailed monitoring and surveillance of vessel traffic can take place.
Over 2000 vessels a year transit through the waters surrounding Tristan da Cunha, most of which are cargo ships. The main class of fishing vessel in the area is longliners that mainly target tuna and tuna-like species. These longliners pose a threat to the seabirds nesting in the islands. As they dive for food, petrels and albatross are often caught on the baited hooks and are therefore vulnerable to becoming part of the incidental bycatch.
OceanMind, an NGO that works to increase the sustainability of fisheries worldwide, conducts monitoring and surveillance activities on behalf of the UK Government’s Marine Management Organisation (MMO). OceanMind’s fisheries analysts use a wide variety of tools and technologies to provide robust intelligence reports to its partners. Traditional satellite monitoring technologies such as Automatic Identification Systems (AIS), Synthetic Aperture Radar (SAR), and Sentinel-2 optical imagery are used to better monitor the risks of IUU fishing, and are supplemented by Vessel Monitoring System (VMS) data when available. These technologies are highly efficient and effective in helping understand which vessels enter Tristan da Cunha’s waters and, more importantly, what they might be doing.
The main tool used for monitoring vessel tracks is AIS data. AIS is a maritime collision avoidance system that transmits on marine VHF radio and provides information on a vessel’s position, speed, course and identity. While AIS is mandatory on all passenger vessels and merchant vessels over 300 gross tons, some flag-states give their fishing vessels exemptions, so it doesn’t always provide a complete picture. Therefore, SAR and Sentinel-2 optical imagery is used to help identify vessels that either have no AIS or have chosen to turn it off to remain ‘unseen’. But even with these technologies combined, some vessels can go unseen.
When monitoring vessel activity for Tristan da Cunha from January-March 2017, OceanMind conducted two activities: a fisheries review to build a picture of fishing activity overall in the EEZ and surrounding 100-nm area, and a compliance monitoring review to gauge illegal fishing activity there. The latter would help inform the efficient and effective deployment of monitoring assets to help maximise fisheries compliance in the area.
During the 3-month compliance monitoring review, OceanMind identified 66 detections that may have been related to illegal fishing activity that could not be correlated on AIS. Of these detections, 16 were of high confidence and tallied with a group of fishing vessels identified with the characteristics of longliners and squid jiggers. These ‘dark’ vessels were persistent, which suggested that they continuously operate in and around Tristan da Cunha with their AIS transmitters turned off. Southern Bluefin and Albacore tuna have a considerable monetary value to fishers, which makes them highly prized and a potential target of IUU fishing.
It is in these circumstances where a relatively new technology known as VIIRS is beneficial. NASA’s Visible Infrared Imaging Radiometer Suite technology is a scanning radiometer that collects visible and infrared imagery, as well as radiometric measurements from the surface of the earth. The technology’s “Day/Night Band” sensor, which collects nightly observations of light emissions present on the ocean surface, is particularly useful to OceanMind’s monitoring work. Most of these light sources come from vessels at sea and, more specifically, fishing vessels that use light to attract catch.
More recently, when OceanMind again analysed the waters around Tristan da Cunha, a total of 62 VIIRS detections were identified. Four of these were close to seamounts near Gough Island where tuna are known to aggregate, and uncorrelated against the other known vessels in the area. (The other vessels were permitted to be there.) The four uncorrelated vessels were classified as potentially conducting IUU fishing activities, which would not have been spotted otherwise.
Throughout OceanMind’s monitoring activity for the islands, its findings showed that, thankfully, the waters around Tristan da Cunha are largely compliant on the whole with no particular fishing fleet posing a significant threat. However, IUU fishing can and does take place. By using new complementary technologies such as VIIRS to help identify when and where this might be happening, the local authorities are better informed and can act quickly to further strengthen their enforcement capabilities.