I wonder if they're accidental or deliberate introductions?

Surprise is the consequence of shock and confusion induced by the deliberate or incidental introduction of the unexpected.

Wildlife biologists resisted these efforts, saying that deliberate introduction of a non-native species would be ecologically unsound and might have detrimental consequences.

There are concerns about non-native signal crayfish becoming dominant in the river, and reports of a deliberate introduction.

The deliberate introduction of cats and the accidental introduction of rats devastated small bird populations.

As a result of escapes and deliberate introductions in the mid-20th century, the raccoon is now distributed in several European and Asian countries.

For a moment they stood silent, after what seemed a deliberate introduction to each other, and Cassandra watched her crossing the room.

With human colonisation came many accidental or deliberate introductions of mammals and birds.

Indeed it appears to derive from a deliberate introduction by humans.

Pollution arrives from land via runoff, the wind and "injection" (deliberate introduction, e.g., drainpipes).