Not even whales on their way to sex and dinner are immune to San Francisco's charms, as in recent days at least three have taken a detour from their annual migration down the coast to take a spin in the Bay.

According to the National Park Service, the California gray whale swims as many as 13,000 miles each year, "spending about one third of its life migrating from the cold, nutrient-rich waters of Alaska, to the warm, shallow lagoons of Baja California."

What's the reason for this journey? Food and reproduction, the same reasons I spent what felt like one third of my 20s migrating from my college-era apartment in the Western Addition to the Mission.

"They migrate south in the fall from their Arctic feeding grounds in the Bering, Beaufort, and Chukchi Seas west and north of Alaska down the Pacific coast as far as Baja California, Mexico, to spend the winter in their breeding and calving grounds in warm water lagoons and in the Southern California Bight," the NPS writes.

But like all long trips, a pit stop or two is apparently required. According to KCBS, a mom and her calf made a Valentine's Day visit to Alcatraz and Angel Island, prompting a US Coast Guard warning to all boaters to stay more than 100 yards from the pair.

Then yesterday, another whale was spotted off Pier 9 north of the Ferry Building CBS5 reports.

Ferry operators and other commercial vessels were warned via Coast Guard broadcast to watch out for the whale, which was later spotted just off Pier 23.

Though once hunted to near-extinction, the California Grey Whale population is now at around 20,000, all of whom make migrate down then back up the coast every year. However, according to the NPS, "As the population has recovered, not all gray whales migrate all the way to Alaska, and more are lingering along the Pacific Coast to feed during the summer at places like Point Reyes and the Farallon Islands."

According to the U.S. Coast Guard's San Francisco unit, citizen reports are the best way they can track and protect whales who have wandered into the Bay. Therefore, if you see one, please do give the Coast Guard a call at 415-399-3547, so they can send the word out to boaters and keep them from crashing into our big grey pals.

See all of SFist's whale coverage here.