'Super Mega Dolphin Pod' Off Calif. Coast: 35 Miles Wide, 100,000 Strong? (VIDEO)

A "super mega dolphin pod" was spotted off the San Diego, Calif. coast Thursday, with estimates to be in the tens of thousands. The creatures' gathering spanned over 35 square miles in the Pacific Ocean.

The super mega dolphin pod, as it's come to be known, was witnessed firsthand by Joe Dutra, the captain of a Hornblower Cruises ship. The tour ship was packed with whale watchers when the pod arrived.

"I've seen a lot of stuff out here but this is the biggest I've ever seen," Dutra told NBC 7 San Diego. "When you see something like that it is honestly truly beyond belief. You had to be there to experience it. It was truly spectacular."

 Although it was tough to get an estimate on just how many dolphins there were, Dutra pegged it at up to 100,000, while others say the best guest is probably closer to 10,000. For the lucky passengers of that Hornblower Cruises ship, the sight was fantastic either way— most dolphin pods come in groups of 15 to about 200.

"They were coming from all directions, you could see them from as far as the eye can see," Dutra added.

The tour group managed to follow the dolphin pod for over an hour, taking pictures and video. Still, the cause of the dolphin frenzy could not be determined by the passengers or captain.

Experts have a few theories as to the reason behind the massive dolphin pod. Thousands of dolphins could have come together for a number of reasons, like a social gathering or to seek out a particularly large food source.

"They're attracted to kind of the same thing, they might wind up in the same place," Sarah Wilkin, a U.S. marine expert, told NBC. She speculated that many squid, herring, or sardines could pull several already large pods together, and other experts agreed.

"In my experience it's all about the food," Peter Wallerstein, head of California's Marine Animal Rescue, was quoted by Daily Mail. There is so much squid in the water at the moment and that is what the dolphins are chasing. The big pods are usually a little bit further offshore but they are following the food source."

"Super mega-pods" of 10,000 are sometimes seen, Wallerstein said, but usually further offshore.