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Global Fishing Watch’s open data is used in this report. Global Fishing Watch uses data about a vessel’s identity, type, location, speed, direction and so on which is broadcast using the automatic identification system (AIS) and collected via satellites and terrestrial receivers. AIS was originally developed to avoid collisions and for safety. Global Fishing Watch analyzes AIS data collected from vessels that our research has identified as known or possible commercial fishing vessels, and applies a fishing detection algorithm to determine “apparent fishing activity” based on changes in vessel speed and direction. The algorithm classifies each AIS broadcast data point for these vessels as either apparently fishing or not fishing and shows the former on the Global Fishing Watch fishing activity heat map. AIS data broadcast may vary in completeness, accuracy and quality. Also, data collection via satellites or terrestrial receivers may introduce errors due to missing or inaccurate data. Global Fishing Watch’s fishing detection algorithm is a best effort mathematically to identify “apparent fishing activity.” As a result, it is possible that some fishing activity is not identified as such by Global Fishing Watch; conversely, Global Fishing Watch may show apparent fishing activity where fishing is not actually taking place. For these reasons, Global Fishing Watch qualifies designations of vessel fishing activity, including synonyms of the term “fishing activity,” such as “fishing” or “fishing effort,” as “apparent,” rather than certain. Any Global Fishing Watch information about “apparent fishing activity” should be considered merely an estimate and must be relied upon solely at your own risk. Global Fishing Watch is taking steps ensure fishing activity designations are as accurate as possible. Global Fishing Watch fishing detection algorithms are developed and tested using actual fishing event data collected by observers, combined with expert analysis of vessel movement data, resulting in the manual classification of thousands of known fishing events. Global Fishing Watch also collaborates extensively with academic researchers through our research program to share fishing activity classification data and automated classification techniques.

The International Maritime Organization (IMO) requires AIS use by all vessels >500GT, for any vessel >300GT that is on an “international voyage” and for all passenger vessels: IMO Revised Guidelines for the Onboard Operation Use of Shipborne AIS – A.1106(29) 22 AIS should always be in operation when ships are underway or at anchor. If the master believes that the continual operation of AIS might compromise the safety or security of the ship, or where security incidents are imminent, AIS may be switched off. Unless it would further compromise the safety or security, if the ship is operating within a mandatory ship reporting system, the master should report this action and the reason for doing so to the competent authority.
In addition, many countries and intergovernmental agencies such as regional fisheries management organizations are creating AIS requirements within their waters, so we expect an increase in AIS use in the coming years. For example, as of May 31, 2014, all European Union flagged fishing vessels over 15 meters (m) in length are required to be equipped with AIS and as of March 1, 2016, all commercial U.S. flagged fishing vessels over 65 feet in length are required to be equipped with AIS.
Two key factors that affect the completeness and accuracy of footprints derived from AIS analysis are its use and reception. AIS must be installed and broadcast in order to be detected. AIS reception is a measure of how likely it is for a vessel’s AIS message to be received correctly by the existing network of satellites and terrestrial antennas placed along the world’s coastlines. In regions of the world with high maritime traffic, AIS signals can interfere with each other, reducing reliable satellite reception.
A recent study by the Food and Agriculture Organization of the United Nations and Global Fishing Watch found that in the Mediterranean almost 100 percent of vessels over 15 m use AIS. However, AIS captures mostly trawlers and purse seiners and often fails to capture other gears that are commonly used by smaller vessels in the Mediterranean, such as set-gillnets or long-liners. In fact, around 50 percent of the Mediterranean fleet comprises vessels less than 12 meters in length. Fishing activity in the Southeastern Mediterranean Sea is poorly represented in AIS data compared to the Northern part of the Mediterranean. The lack of AIS use in this area is mainly due to limited on-board transmitters and terrestrial receptors.
This report is an output of the Med Sea Alliance, a movement created in 2020 to bring together non-governmental organizations and other citizens’ groups working to improve the health and productivity of the Mediterranean Sea. As a member of the Med Sea Alliance, Global Fishing Watch has contributed to the AIS-based analysis included in this report. The designations employed and the presentation of the material in this report do not imply the expression of any opinion whatsoever on the part of Global Fishing Watch and the Med Sea Alliance concerning the legal status of any country, territory, city or area, including protected areas, or of its authorities, or concerning the delimitation of its frontiers or boundaries.
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MedSeaAlliance 2022, Atlas of bottom trawling in protected areas in the Mediterranean Sea https://www.medseaalliance.org/