I do not think there are many doors in the Arctic, and fewer under water. Let's substitute the doors for blocks of ice. These will move in some way to prevent the whale access elsewhere. To do this, we must finish the previous example.
Before you begin, we need to move the trap iceberg when the whale approaches or leaves it. The icebergs that blocked the way will remain fixed in their positions.
iceberg_son, which will serve as the trapdoor.
Scale the middle iceberg down so that it is smaller than the ...