The divers didn't know what they were doing.
Would anyone sit next to a carcass waiting for a lioness to bring her cubs? Well that is essentially the same thing.
The whales are evident from the beginning of the film loop in the distance, there are shore birds everywhere feeding on small fish at the surface. This is a common scene when large mammals feed.
At one point the camera falls below the water to expose lots of small fish. That is what the whales came to feed on. There is a bait ball (a group of small silver fish) to the left. They form a ball to defend themselves from predation. The deeper into the ball a fish is the less likely they will be picked up by the birds or smaller fish.
Marine mammals don't have that problem. Dolphins swim directly through these fish and feed. Whales come up from underneath and use their baleen to syphon the fish out of the water. The whales are in their territory and feeding.
The divers should not be in those water. They don't know what they are doing and are illegally interfering with the whales. These whales are endangered. Humans are not suppose to have contact with them. It is the divers that are wrong. If they don't know that or understand that, then they educate themselves about the oceans of the world.
This is the issue and the bait ball can't be seen from the surface UNLESS one knows what they are looking at. This bait ball is fed on by tuna and dolphin. It is not unusual for tuna and dolphin to feed together. Dolphin Free Nets.
The sea birds can even be seen diving into the water to feed.By the end of the film look the bait ball is nearly gone. It fed a lot of birds, tuna and dolphin. If there were whales in the area they would have come up from beneath and simply opened those jaws lined with baleen and taken a good swallow of it.
In the film loop at top it is uncertain what the whales may have thought was at the surface. They might have thought there were dolphins or some other large fish. They didn't care if they scared them off, they wanted to eat. The divers should not have been in the water with all that feeding happening. Foolishness.
There was something on the surface the whales were interested in because the birds came in to clean it up. Those whales were in a hurry, too. There was strong effervesce of gas coming up from underneath that surfaced about a second or so before the whales were seen. They were moving. They were displacing water and causing foaming under the water. They felt their feeding ground was threatened.
The fin that stayed on the surface was to attempt to chase the birds off so they could feed some more. It probably slapped the surface to scare the birds off.
