It was a thrilling scene for whale watchers Sunday in Dana Point, Calif.: "Oh my gosh, they are mating right there," whale watcher Tom Southern said while videotaping the event on Capt. Dave's Dolphin and Whale Watching Safari. "Look at that, he's thrashing, trying to push up against her."

Southern, along with his fellow whale watchers, captured on video two gray whales bumping up against each other in a mating ritual that usually occurs in a lagoon located 600 miles south of Orange County.

"Whenever we have unusual behavior from whales, it is always exciting to see," Capt. Dave Anderson of Capt. Dave's Dolphin and Whale Watching Safari told ABCNews.com. "A couple of times a year we have some mating behavior that happens along the migration route, and it was pretty exciting to see this so close to the boat."

The whales, which mature sexually between the ages of 6 and 12, were joined by dolphins; the dolphins seemed to be participating in the mating ritual by swimming in between and around the whales, Anderson said.

"It was surprising how connected they were to the whole show," he said of the dolphins. "They weren't involved in mating but were very involved in the observation and frolicking."

The whale-watching captain also said female gray whales usually had multiple partners, making this encounter rare.

"What is interesting is that there were only two whales involved, because usually the female whale has three to four involved in the mating, with the last male fathering the calf," Anderson said. "It was unusual in that there was one male and no other males involved in it."

These gray whales typically make the three month, 6,000 mile swim from the Arctic Ocean near Alaska to Baja, Calif., to mate, making this the longest migration for any mammal on earth, said Anderson.

Gray whales also typically mate in a lagoon, because it is safe from predators like killer whales, he said. Along their journey from the Arctic Ocean, there are nearly 150 killer whales waiting to kill them for food.

"Up to about 35 percent of gray whales can be killed by killer whales during calving," Anderson said. "If they mate in the lagoon, the next year they will be in that same lagoon to give birth."

These whales usually give birth to one calf after the gestational period, which is between 12 to 13 months, he said. The mother will stay in the lagoon for a short period of time to feed the calf with her milk, and then make the long trek back to the Arctic.

Killer whales aren't the only threats facing gray whales in the open ocean. Anderson said 1,000 whales and dolphins die every day because of fishing gear entanglement.

"Just in this last year I was involved in disentangling three gray whales, and we have reports that there is another that may be making its way toward us any day now from San Diego," he said. "It is a big problem and most are not aware of it. God has blessed Southern California with more dolphins and blue whales than anywhere in the world. We have an amazing amount of sea life we need to protect and people should come and see."