Then with a few farewell tail slaps, they are gone: some off into the fjord, others out to sea.
We make a note of each time these events occur, or any other behavior that is out of the ordinary, like tail slaps and pinwheeling.
Simon Oliver, a marine biologist at the Thresher Shark Research and Conservation Project in the Philippines, said the sharks' "tail slaps" reached a speed of 24 metres per second, or more than 50mph.
"These overhead tail slaps cause explosive shockwaves in the water that we think are part of the hunting mechanism," Oliver told the Guardian.
There are no jumps, just some happy tail slaps – reminders for the herring to stay in a nice tight ball – easier for them to swallow.
The team analyzed the videos in the lab and characterized the sharks' overhead tail slaps into four phases: preparation, strike, wind-down recovery, and prey item collection.
Killer whales in the North Sea use wolf-like howls to round up the herring shoals which they feed on, and they and other dolphins also use percussive tail slaps and splashing leaps to signal to each other.
The orcas employed a tail outward and tail slapping defensive position against the bull sperm whale similar to that used by female sperm whales against attacking orcas.
If you notice a rapid change in their swimming pattern, lots of surface displays (tail slapping) or females shielding their calves with their bodies, leave the area immediately.
Behaviors include breaching, spyhopping, lob-tailing, tail-slapping, fin-slapping, peduncle throws, charging and parrying.
