1. Sperm whales hang out in groups of about 10 females with their calves. If a killer whale attacks, calves will be surrounded by the adults for protection. Sperm whales also use this strategy to protect injured whales.
2. Some dolphins coordinate their feeding by surrounding a school of fish in a circle. Then the dolphins take turns feeding while the fish are trapped.
3. Sea otters use rocks or bottles (the only example I’ve heard of trash being useful) to break open sea urchins and shellfish.
4. Short-finned pilot whales nurse some of their calves for 13 to 15 years! To all the women out there, can you even imagine that? Nursing and teaching your child to drive at the same time.
5. Transient killer whales use a much more stealth form of echolocation to hunt marine mammals than resident killer whales that just eat fish.