The Northern California coast tends to get its fair share of sightings of humpback whales and gray whales, but the largest mammals on earth, blue whales, don't do swim-bys quite so often as other species. This year, all rules are out the window, so it stands to reason we're getting a visitation by a gang of blue whales too.

If blue whales make it near the Bay Area during their migration in a given year it's typically around August or September. But this year, dozens of the ginormous creatures have made a pit stop around the Farallon Islands to feast on krill — the two-inch, shrimp-like crustaceans that make up the bulk of the whales' diet. And that's prompted a warning from marine biologists to ships coming in and out of the Golden Gate, because the whales tend to be distracted with feeding when the food is abundant and might not be aware of a huge ship in their midst.

47 of the creatures were spotted in one hour near the Farallones on June 13, and 23 were spotted the day before, as KPIX reports.

Blue whales, which can get up to 100 feet long, can eat up to six tons of krill per day, and for feeding purposes they tend to congregate closer to the continental shelf, where the crustaceans are more prevalent. Cold upswells in the ocean current can bring a krill bounty closer to shore, and the whales will then follow — something that happened in early summer in 2012, and again in 2013.

"Their enormous size dictates that they maximize feeding effort when food is available, and this sometimes takes them into dangerous waters," says Maria Brown, superintendent of the Greater Farallones National Marine Sanctuary in a statement. "While focused on feeding, they are not likely to recognize or evade a ship’s approach."

The huge number of whales spotted on the 13th took experts by surprise, and NOAA Greater Farallones spokeswoman Mary Jane Schramm tells KPIX, "It’s extraordinary. It may be an absolute record."

As the Press-Democrat reports, scientists and conservationists get especially anxious about protecting the blue whale population in the northeast Pacific, which numbers around 1,650 and hasn't grown much over the last 30 years. The whales have no primary predator — though they are sometimes taken down by a pack of killer whales — so the most common killers of the whales tend to be ship strikes.

This year saw a particularly massive migration of gray whales near the Marin County coast in early March, with over 200 sightings in just two days. And both gray and humpback whales make annual spring migrations to the food-rich waters of Alaska, taking them past the NorCal coast.

Blue whales migrate between the waters off Mexico and California up to the Pacific Northwest, taking their time on their spring and summer journey north to pause and feed wherever krill blooms occur. A 2019 study of the whales found that they rely on memory to chart these migrations, apparently using ten-year averages of where krill tend to spring up, rather than chasing them specifically year to year.

Climate change may be mucking up how these averages work — specifically where chlorophyll tends to be most abundant, which in turn attracts big blooms of krill. And as The Atlantic reported last year, that could lead to whale populations "missing" their food as they travel to locations based on memories of where it was most available in the past.

Related: Over 200 Gray Whales Passed By Point Reyes Over the Weekend