Surfing, we take it as, taking a board to the water and staying on a wave until it hits the shore. The "surf" however is a noun referring to the waves in the water. Technically, you could say a dolphin was "surfing" because you are referring to an activity done on what is termed the surf.
I have seen Dolphins surfing in front of the bows of ships, while in the Navy.
They use to tag along and sort of race us, riding the waves as the bow broke the water........
I have a few good shots, I took while leaning over one of the Bridge wings. One was actually printed in the ships newspaper.
Have seen them playing but not surfing in real life before.
This filmmaker claims there were about 150 playing in the surf:
https://au.news.yahoo.com/thewest/wa/a/24227196/dolphins-catch-a-wave/
