"A 2018 review of Maritime Transport (UNCTAD) calculated that there are 50,732 active ships around the world—including those at seas and in port.

There are many ways to keep track of all this traffic and do maritime tracking. AIS tracking websites such as the aptly named MarineTraffic operate over 2000 automatic identification system (AIS) stations in over 165 countries across the globe."

https://up42.com/blog/a-complete-guide-to-marine-traffic-tracking-tech-and-ais-data