Dolphins leaped and performed off the Orange County coast Sunday for William Nelson of Laguna Niguel, who captured the animals in action as he rode past in a boat.

Nelson first encountered a group of perhaps 20 to 25 Risso’s dolphin about a quarter mile off Newport Beach.

It’s an odd species unseen in local waters before 1982, said Orange Coast College marine science professor Dennis Kelly.

Over time, the Risso’s might have chased away populations of pilot whales, which also eat squid and were once common, but whose local numbers have since dropped.

Later in the day, Nelson came across what Kelly identified as “offshore” bottlenose dolphins, a group that is larger and more sleek than the “coastal” bottlenose.

These were perhaps two miles off Laguna Beach.

A few bottlenose can sometimes be found mixed in with groups of Risso’s, and the Risso’s sonar abilities could be the key.

Both have “melon” organs in their heads that are used to find prey by echolocation. But in Risso’s, the melon is split, which might allow a kind of “Doppler sonar,” making them more sensitive, and better at finding squid, than the bottlenose dolphins, Kelly said.

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