This reminds me of a documentary I watched last decade called "Strange days on planet Earth", narrated by Edward Norton. One of the episodes was about this unwa

This reminds me of a documentary I watched last decade called "Strange days on planet Earth", narrated by Edward Norton. One of the episodes was about this unwanted migration. They suspended a rubber ring in the water in one of the ports and a few months later found that about 90% of the animals living on that ring were hitchhikers from a long way away.