Quantifying marine vessel traffic from aerial surveys in the Salish Sea

There are a number of potential impacts associated with vessel traffic on marine ecosystems, including noise and oil pollution, ship-strikes, and fishing and fisheries bycatch. To assess these impacts, many studies employ marine traffic data collected using Automatic Identification Systems (AIS) onboard vessels. However, AIS only captures a fraction of the actual marine traffic because it omits many of the smaller vessels, which are not legally required to carry AIS. Without this information, the assessment of vessel-associated impacts based on AIS is inherently flawed, and underestimated. The NEMES (Noise Exposure to the Marine Environment from Ships) project is particularly interested in this unknown component of marine traffic as non-AIS vessels are likely contributing a considerable amount of noise in the Salish Sea. With the assistance of the National Aerial Surveillance Program (NASP), we have been collecting vessel traffic information for both AIS and non-AIS vessels during two years (2016, 2017) in parts of the Salish Sea. The AIS receiver and sensors onboard the NASP aircraft can collect AIS information and video with positional information of target objects such as vessels. The video also allows the characterization of the vessel type (e.g., sailboat, motorboat, fishing vessel) and vessel activity (i.e., fishing, motoring or sailing). Results indicate that non-AIS vessels contribute at least 60% of the overall vessel traffic in surveyed areas between 2016 and 2017. The majority of these non-AIS vessels are recreational vessels, particularly during the summer months and near popular touristic destinations such as the Southern Gulf Islands. Through this work, we are now able to build a more complete picture of the distribution and type of vessels using the Salish Sea, and have a better understanding of their potential impacts to the marine ecosystem.