I love coming home at 3am, turning the TV on, and getting good programs on Animal Planet. I've seen this episode before (Called "Massive Nature," shmoo, not "Blue Planet") before and blogged about it. Yesterday's viewing was from the beginning though. The particular segment that I stayed awake to watch was the sardine bait ball. (Come on, even at 3am, the mention of a sardine bait ball should always excite you)
The dolphins separated the pack of sardines (called a bait ball) from the main pack by blowing bubbles into the pack of fish. Afterwards, the sharks, birds, and seals joined in. The rest you can see in my previous post. The program concludes that "becoming separated is what made these fish vulnerable" and that the sardines' doom was facilitated because "these predators have ignored each other (because of how easy it is to hunt sardine bait balls)".
So... stick with the pack. If you show weakness, every one will want a piece of you.